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Android 2.3 (Gingerbread) released

Yesterday Google fially released the long-anticipated Android 2.3 (Gingerbread). <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/December/Android%202.3_1/gingerdroid.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" ox="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/December/Android%202.3_1/gingerdroid.png" /></a></div>here are some of the new features: <ol><li>API Level: 9.</li><li>The Dalvik VM introduces a new concurrent garbage collector that produces a smoother and faster performance.</li><li>Session Initiation Protocol (SIP) based VoIP API to build telephony applications.</li><li>Near Field Communication (NFC) API.</li><li>New Sensors: Gyroscope (for measuring orientation), barometer (for measuring atmospheric pressure), sensors for gravity and acceleration.</li><li>Support for multiple cameras: the camera API can detect multiple cameras in the device and add new capabilites for shooting such as managing focus.</li><li>Usage of third-party video drivers: improves the performance of OpenGL ES.</li><li>Audio Effects: new audio effects such as bass boost, reverb and equalization.</li><li>New Downlaod Manager: handles downloading files in the background.</li><li>Strict Mode: helps developers to optimize their code by detecting disk or network usage that could degrade the performance of the application.</li></ol>and here's the official release video: <object height="385" width="640"><param name="movie" value="http://www.youtube.com/v/Jx3pdWBlZ34?fs=1&hl=en_US"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/Jx3pdWBlZ34?fs=1&hl=en_US" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="385"></embed></object>

Yesterday Google fially released the long-anticipated Android 2.3 (Gingerbread). here are some of the new features: API Level : 9. The Dalvi...

Android Content Providers

Remember when we created a sqlite database android application. We saw that the database file is stored in the file system directories of that application meaning that the database cannot be accessed from another application. You can apply the same thing on any resources within your application (Files, images, videos, …). <div class="MsoNormal" style="margin: 0in 0in 10pt;">But there is a method to expose your data across multiple applications: Content Providers.</div><div class="MsoNormal" style="margin: 0in 0in 10pt;">Content Providers expose an application’s data across all other applications, you can use content providers to store or retrieve data of one application from any other application.</div><div class="MsoNormal" style="margin: 0in 0in 10pt;">In this post we’re going to see how to deal with the existing default content providers by retrieving and manipulating data through them.</div><div class="MsoNormal" style="margin: 0in 0in 10pt;">Android default content providers:</div><div class="MsoNormal" style="margin: 0in 0in 10pt;">There are many built-in content providers supplied by OS. They are defined in the android.provider package, they include:</div><div class="MsoListParagraphCxSpFirst" style="margin: 0in 0in 0pt 0.5in; mso-list: l0 level1 lfo1; text-indent: -0.25in;">·         Browser.</div><div class="MsoListParagraphCxSpMiddle" style="margin: 0in 0in 0pt 0.5in; mso-list: l0 level1 lfo1; text-indent: -0.25in;">·         Calllog.</div><div class="MsoListParagraphCxSpMiddle" style="margin: 0in 0in 0pt 0.5in; mso-list: l0 level1 lfo1; text-indent: -0.25in;">·         Live Folders.</div><div class="MsoListParagraphCxSpMiddle" style="margin: 0in 0in 0pt 0.5in; mso-list: l0 level1 lfo1; text-indent: -0.25in;">·         Contacts Contract.</div><div class="MsoListParagraphCxSpMiddle" style="margin: 0in 0in 0pt 0.5in; mso-list: l0 level1 lfo1; text-indent: -0.25in;">·         Media Store.</div><div class="MsoListParagraphCxSpLast" style="margin: 0in 0in 10pt 0.5in; mso-list: l0 level1 lfo1; text-indent: -0.25in;">·         Settings</div><div class="MsoListParagraphCxSpLast" style="margin: 0in 0in 10pt 0.5in; mso-list: l0 level1 lfo1; text-indent: -0.25in;"> </div>content providers basics: the concept of content providers is pretty similar to the concept of ASP.NET Web Services they provide data encapsulation through exposing data by URis. Any content provider is invoked by a URi in the form of content://provider_name . for example the URi of the Contacts content provider that retrieves all contacts is in the following form content://contacts/people. If you want to retrieve a particular contact (by its ID) then it would be in this form: content://contacts/people/5. You do not need to write the URis of the content providers manually as they are stored as constant values in their respective content provider classes. The Uri of the Contacts phones content provider is defined in <pre class="brush:java">ContactsContract.CommonDataKinds.Phone.CONTENT_URI</pre>(content://com.android.contacts/data/phones) The Uri of the browser Bookmarks content provider is defined in <pre class="brush:java">Browser.BOOKMARKS_URI</pre>(content://browser/bookmarks) The Media store (Video) stored in external device (SD Card) is defined in <pre class="brush:java">MediaStore.Video.Media.EXTERNAL_CONTENT_URI</pre>(content://media/external/video/media) and so on. content providers allow you to perform basic CRUD operations: Create,Read, Update and Delete on data. Making Queries to retrieve data from a content provider we run a sql-like query using ManagedQuery object. The ManagedQuery object returns a cursor holding the result set. To retrieve a list of all contacts and display them in a ListView We first define our activity xml layout: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/txt" /> <ListView android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/list" /> </LinearLayout> </pre>And define the layout of each row in the ListView: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="wrap_content" android:layout_height="wrap_content" android:orientation="horizontal" > <TextView android:layout_width="100px" android:layout_height="wrap_content" android:id="@+id/txtName" android:layout_weight="1" /> <TextView android:layout_width="100px" android:layout_height="wrap_content" android:id="@+id/txtNumber" android:layout_weight="1" /> </LinearLayout> </pre> Remember to add the following permission to the manifest.xml file <pre class="brush:xml"><uses-permission android:name="android.permission.READ_CONTACTS"></uses-permission> </pre> To retrieve the contacts and bind them to the listView: <pre class="brush:java">String [] projection=new String[]{ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME,ContactsContract.CommonDataKinds.Phone.NUMBER,ContactsContract.CommonDataKinds.Phone._ID}; txt.setText(ContactsContract.PhoneLookup.CONTENT_FILTER_URI.toString()); Uri contacts = ContactsContract.CommonDataKinds.Phone.CONTENT_URI; Cursor managedCursor = managedQuery(contacts,projection,null,null,null); //Cursor managedCursor =cr.query(contacts, projection, null, null, null); ListAdapter sca=new SimpleCursorAdapter(this,R.layout.listrow,managedCursor,projection,to); list.setAdapter(sca); </pre> the above code retrieves all the contacts in the following steps: <ol><li>We first define the projection of our query, we define the columns we want to retrieve in the result set.We define a String array containing the names of the columns we want to retreieve.The contacts column names are defined in ContactsContract.CommonDataKinds.Phone class.Note that we need to retrieve the _ID column as the cursor that retrieves the data expects such a column to be there.</li><li>We specify the Uri of the content provider ContactsContract.CommonDataKinds.Phone.CONTENT_URI</li><li>We retrieve the data by a cursor Cursor managedCursor = managedQuery(contacts,projection,null,null,null);The cursor is retrieved by executing a managedQuery which has the following parameters: <ol><li>The Uri of the content provider.</li><li>A String Array of the columns to be retrieved (projection)</li><li>Where clause.</li><li>String array containing selection arguments values.</li><li>String representing the order by clause, we can use it but here it will be null. If we want to sort the contacts by name it would be ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME +“ asc”</li></ol></li><li>Then we create a list adapeter using the cursor and bind the ListView to it.</li></ol> The previous example retrieves all the contacts but what if we want to retrieve a certain contact by name: There are two ways: <ol><li>Using the same code above but adding a where clause and selection arguments to the managed wuery so it becomes like this: <pre class="brush:java">Cursor managedCursor = managedQuery(contacts,projection,ContactsContract.CommonDataKinds.Phone.DISPLAY_NAME+"=?",new String[]{"Jack"},null);</pre>This retrieves contact info of a person named Jack.</li><li> The other method is to inject the query in the Uri, instead of using Uri <pre class="brush:java">contacts = ContactsContract.CommonDataKinds.Phone.CONTENT_URI;</pre>we use <pre class="brush:java">Uri contacts=Uri.withAppendedPath(ContactsContract.CommonDataKinds.Phone.CONTENT_FILTER_URI,Uri.encode("Jack"));</pre>This is equivalent to the following Uri content://com.android.contacts/data/phones/Jack</li></ol> Inserting,updating and deleting: to insert data using a content provider there are two methods First: Using the Insert() method of your activity’s content resolver object. Like this example t insert a new bookmark to the browser: <pre class="brush:java">ContentValues cv=new ContentValues(); cv.put(Browser.BookmarkColumns.TITLE, "End Gadget"); cv.put(Browser.BookmarkColumns.URL, "http://www.engadget.com/"); cv.put(Browser.BookmarkColumns.BOOKMARK,1); Uri u= getContentResolver().insert(Browser.BOOKMARKS_URI, cv); </pre> We create a ContentValues object and add to it all the required fields, then we call getContentResolver().insert method which returns the Uri of the newly inserted item. It would be in this example content://browser/bookmarks/17 We can use the generated Uri to update or delete the item later. Second: We can replace the getcontentresolver().insert() method with bulkInsert method if we want to insert multiple items at a time. The bulkInsert(Uri url,ContentValues[] values) method returns the number of new items created. Updating info using Content Providers: To update data using content providers, we use getContnetResolver.Update() method: This code updates the title of an existing browser bookmark: <pre class="brush:java">ContentValues cv=new ContentValues(); cv.put(Browser.BookmarkColumns.TITLE, "End Gadget mod"); //uriBook= getContentResolver().insert(Browser.BOOKMARKS_URI, cv); getContentResolver().update(Browser.BOOKMARKS_URI, cv, BookmarkColumns.TITLE+"=?", new String[]{"End Gadget"}); </pre> the Update method has the following parameters: <ul><li>Content Providers Uri</li><li>ContentValues object having the new values</li><li>Where clause</li><li>String array of the where clause arguments values</li></ul> Deleting info using Content Providers: To delete info we use getContentResolver.Delete() method To delete a bookmark: <pre class="brush:java">getContentResolver().delete(Browser.BOOKMARKS_URI,BookmarkColumns.TITLE+"=?", new String[]{"End Gadget"});</pre> the delete function has the following parameters: <ul><li>Content Providers Uri</li><li>Where clause</li><li>String array of the where clause arguments values</li></ul> Remember to add the following permissions to the manifest.xml to add and read browser bookmarks: <pre brush:xml=""><uses-permission android:name="android.permission.WRITE_CONTACTS"></uses-permission> <uses-permission android:name="com.android.browser.permission.WRITE_HISTORY_BOOKMARKS"></uses-permission> </pre>

Remember when we created a sqlite database android application. We saw that the database file is stored in the file system directories of th...

How to check if the phone is connected to the Internet

to check whether your phone is connected to the Internet, use the following code: <pre class="brush:java">ConnectivityManager con=(ConnectivityManager)getSystemService(Activity.CONNECTIVITY_SERVICE); boolean wifi=con.getNetworkInfo(ConnectivityManager.TYPE_WIFI).isConnectedOrConnecting(); boolean internet=con.getNetworkInfo(ConnectivityManager.TYPE_MOBILE).isConnectedOrConnecting(); </pre> these lines check for internet connection whether it is through WiFi or Mobile Internet. you need to add the following permission to the AndroidManifest.xml file <pre class="brush:xml"><uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> </pre> Another method is what our freind Kevin mentioned in the comments, is to check if a certain website is reachable or not like this: <pre class="brush:java">public static boolean isOnline() { try { InetAddress.getByName("google.ca").isReachable(3); return true; } catch (UnknownHostException e){ return false; } catch (IOException e){ return false; } } </pre> we check if a site is reachable within a certain timeout or not.

to check whether your phone is connected to the Internet, use the following code: ConnectivityManager con=(ConnectivityManager)getSystemServ...

Using SQLite Database with Android

Android default Database engine is Lite. SQLite is a lightweight transactional database engine that occupies small amout of disk storage and memory, so its a perfect choice for creating databases on many mobile operating systems such as Android, iOS. Things to consider when dealing with SQLite: <ol><li>Data type integrity is not maintained in SQLite, you can put a value of a certain data type in a column of another dataype (put string in an integer and vice versa).</li><li>Referential integrity is not maintained in SQLite, there is no FOREIGN KEY constraints or JOIN statements.</li><li>SQLite Full Unicode support is optional and not installed by default.</li></ol> In this tutorial we will create a simple database application to store employees data. the DB has: Tables: <ol><li>Employees </li><li>Dept.</li></ol>Views: <ol><li>ViewEmps: to display employees and their relative departments.</li></ol> <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/October/SQLite%20DB/sqlitedb1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" ex="true" height="133" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/October/SQLite%20DB/sqlitedb1.jpg" width="320" /></a></div> Creating SQLite Database By default SQLite on Android does not have a management interface or an application to create and manage data bases from, so we're going to create the database ourselves by code. First we will create a class that handles all the operations required to deal with the database such as creating the database, creating tables, inserting and deleting records and so on. The first step is to create a class that inherits from SQLiteOpenHelper class. this class provides two methods to override to deal with the database: <ol><li>onCreate(SQLiteDatabase db): invoked when the database is created, this is where we can create tables and columns to them, create views or triggers.</li><li>onUpgrade(SQLiteDatabse db, int oldVersion, int newVersion): invoked when we make a modification to the database such as altering, dropping , creating new tables.</li></ol> our class will have the following members <pre class="brush:java">public class DatabaseHelper extends SQLiteOpenHelper { static final String dbName="demoDB"; static final String employeeTable="Employees"; static final String colID="EmployeeID"; static final String colName="EmployeeName"; static final String colAge="Age"; static final String colDept="Dept"; static final String deptTable="Dept"; static final String colDeptID="DeptID"; static final String colDeptName="DeptName"; static final String viewEmps="ViewEmps"; </pre> The Constructor: <pre class="brush:java">public DatabaseHelper(Context context) { super(context, dbName, null,33); } </pre> The constructor of the super class has the following parameters: Context con: the context attached to the database. dataBaseName: the name of the database. CursorFactory: some times we may use a class that extends the Cursor class to implement some extra validations or operations on the queries run on the database. In this case we pass an instance of CusrsorFactory to return a reference to our derived class to be used instead of the default cursor, In this example we are going to use the standard Cursor Interface to retrieve results, so the CursorFactory parameter is going to be null. Version: the version of the schema of the database. The constructor creates a new blank database with the specified name and version. Creating the database: The first superclass method to override is onCreate(SQLiteDatabase db): <pre class="brush:java">public void onCreate(SQLiteDatabase db) { // TODO Auto-generated method stub db.execSQL("CREATE TABLE "+deptTable+" ("+colDeptID+ " INTEGER PRIMARY KEY , "+ colDeptName+ " TEXT)"); db.execSQL("CREATE TABLE "+employeeTable+" ("+colID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+ colName+" TEXT, "+colAge+" Integer, "+colDept+" INTEGER NOT NULL ,FOREIGN KEY ("+colDept+") REFERENCES "+deptTable+" ("+colDeptID+"));"); db.execSQL("CREATE TRIGGER fk_empdept_deptid " + " BEFORE INSERT "+ " ON "+employeeTable+ " FOR EACH ROW BEGIN"+ " SELECT CASE WHEN ((SELECT "+colDeptID+" FROM "+deptTable+" WHERE "+colDeptID+"=new."+colDept+" ) IS NULL)"+ " THEN RAISE (ABORT,'Foreign Key Violation') END;"+ " END;"); db.execSQL("CREATE VIEW "+viewEmps+ " AS SELECT "+employeeTable+"."+colID+" AS _id,"+ " "+employeeTable+"."+colName+","+ " "+employeeTable+"."+colAge+","+ " "+deptTable+"."+colDeptName+""+ " FROM "+employeeTable+" JOIN "+deptTable+ " ON "+employeeTable+"."+colDept+" ="+deptTable+"."+colDeptID ); //Inserts pre-defined departments InsertDepts(db); } </pre> the method creates tables with columns,a view and a trigger. The method is invoked when the database is created. So we create our table and specify the columns. This method is invoked when the database does not exist on the disk, it’s executed only once on the same device at the first time the application is run on the device. Upgrading the database: some times we want to upgrade the database by changing the schema, add new tables or change column data types. this is done by overriding onUpdate(SQLiteDatabase db,int old Version,int newVerison) method: <pre class="brush:java">public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // TODO Auto-generated method stub db.execSQL("DROP TABLE IF EXISTS "+employeeTable); db.execSQL("DROP TABLE IF EXISTS "+deptTable); db.execSQL("DROP TRIGGER IF EXISTS dept_id_trigger"); db.execSQL("DROP TRIGGER IF EXISTS dept_id_trigger22"); db.execSQL("DROP TRIGGER IF EXISTS fk_empdept_deptid"); db.execSQL("DROP VIEW IF EXISTS "+viewEmps); onCreate(db); } </pre> This method is invoked when the version number specified in the constructor of the class changes. when you want to append a change to your database you must change the version number in the constructor of the class: so when you pass the constructor a version number of 2: <pre class="brush:java">public DatabaseHelper(Context context) { super(context, dbName, null,2); // TODO Auto-generated constructor stub } </pre>instead of 1: <pre class="brush:java">super(context, dbName, null,2); </pre>the application understands that you want to upgrade the database and onUpgrade method will be invoked A typical implementation of this method is to drop the tables and create them again with the additional modifications. Managing Foreign-Key Constraints: we mentioned before that SQLite 3 by default does not support foreign key constraint, however we can force such a constraint using TRIGGERS: we will create a trigger that ensures that when a new Employee is inserted his/her Dept value is present in the original Dept table. the sql statement to create such a trigger would be like this: <pre class="brush:java">CREATE TRIGGER fk_empdept_deptid Before INSERT ON Employees FOR EACH ROW BEGIN SELECT CASE WHEN ((SELECT DeptID FROM Dept WHERE DeptID =new.Dept ) IS NULL) THEN RAISE (ABORT,'Foreign Key Violation') END; END </pre> in onCreate method we created this trigger like this: <pre class="brush:java">db.execSQL("CREATE TRIGGER fk_empdept_deptid " + " BEFORE INSERT "+ " ON "+employeeTable+ " FOR EACH ROW BEGIN"+ " SELECT CASE WHEN ((SELECT "+colDeptID+" FROM "+deptTable+" WHERE "+colDeptID+"=new."+colDept+" ) IS NULL)"+ " THEN RAISE (ABORT,'Foreign Key Violation') END;"+ " END;"); </pre> Executing SQL statements: now let's begin executing basic sql statements. you can execute any sql statement that is not a query whether it is insert, delete, update or anything using db.execSQL(String statement) method like when we did when creating the database tables: <pre class="brush:java">db.execSQL("CREATE TABLE "+deptTable+" ("+colDeptID+ " INTEGER PRIMARY KEY , "+ colDeptName+ " TEXT)"); </pre> Inserting records: we insert records to the databse using the following code for example to insert records in the Dept table: <pre>SQLiteDatabase db=this.getWritableDatabase(); ContentValues cv=new ContentValues(); cv.put(colDeptID, 1); cv.put(colDeptName, "Sales"); db.insert(deptTable, colDeptID, cv); cv.put(colDeptID, 2); cv.put(colDeptName, "IT"); db.insert(deptTable, colDeptID, cv); db.close(); </pre> notice that we need to call this.getWritableDatabase() to open the connection with the database for reading/writing. the ContentValues.put has two parameters: Column Name and the value to be inserted. also it is a good practice to close the database after executing statements. Updating values: to execute an update statement we have two ways <ol><li>to execute db.execSQL</li><li>to execute db.update method:</li></ol><pre class="brush:java">public int UpdateEmp(Employee emp) { SQLiteDatabase db=this.getWritableDatabase(); ContentValues cv=new ContentValues(); cv.put(colName, emp.getName()); cv.put(colAge, emp.getAge()); cv.put(colDept, emp.getDept()); return db.update(employeeTable, cv, colID+"=?", new String []{String.valueOf(emp.getID())}); } </pre> the update method has the following parameters: <ol><li>String Table: the table to update a value in</li><li>ContentValues cv: the content values object that has the new values</li><li>String where clause: the WHERE clause to specify which record to update.</li><li>String[] args: the arguments of the WHERE clause.</li></ol>Deleteing rows: as in update to execute a delete statement we have two ways <ol><li>to execute db.execSQL</li><li>to execute db.delete method:</li></ol><pre class="brush:java">public void DeleteEmp(Employee emp) { SQLiteDatabase db=this.getWritableDatabase(); db.delete(employeeTable,colID+"=?", new String [] {String.valueOf(emp.getID())}); db.close(); } </pre> the delete method has the same parameters as the update method. Executing queries: to execute queries there are two methods: <ol><li>Execute db.rawQuery method.</li><li>Execute db.query method.</li></ol> to execute a raw query to retreive all departments <pre class="brush:java">Cursor getAllDepts() { SQLiteDatabase db=this.getReadableDatabase(); Cursor cur=db.rawQuery("SELECT "+colDeptID+" as _id, "+colDeptName+" from "+deptTable,new String [] {}); return cur; } </pre> the rawQuery method has two parameters: <ol><li>String query: the select statement.</li><li>String[] selection args: the arguments if a WHERE clause is included in the select statement.</li></ol> Notes: <ol><li>The result of a query is returned in Cursor object.</li><li>In a select statement if the primary key column (the id column) of the table has a name other than _id then you have to use an alias in the form SELECT [Column Name] as _id</li>cause the Cursor object always expects that the primary key column has the name _id or it will throw an exception .</ol> another way to perform a query is to use a db.query method. a query to select all employees in a certain department from a view would be like this: <pre class="brush:java">public Cursor getEmpByDept(String Dept) { SQLiteDatabase db=this.getReadableDatabase(); String [] columns=new String[]{"_id",colName,colAge,colDeptName}; Cursor c=db.query(viewEmps, columns, colDeptName+"=?", new String[]{Dept}, null, null, null); return c; } </pre> the db.query has the folowing parameters: <ol><li>String Table Name: the name of the table to run the query against.</li><li>String [ ] columns: the projection of the query i.e the columns to retrieve.</li><li>String WHERE clause: where clause, if none pass null.</li><li>String [ ] selection args: the parameters of the WHERE clause.</li><li>String Group by: a string specifying group by clause.</li><li>String Having: a string specifying HAVING clause.</li><li>String Order By by: a string Order By by clause.</li></ol>Managing Cursors: Result sets of queries are returned in Cursor objects. there are some common methdos that you will use with cursors: <ol><li>boolean moveToNext(): moves the cursor by one record in the result set, returns false if moved past the last row in the result set.</li><li>boolean moveToFirst(): moves the cursor to the first row in the result set, returns false if the result set is empty.</li><li>boolean moveToPosition(int position): moves the cursor to a certain row index within the boolean result set, returns false if the position is un-reachable</li><li>boolean moveToPrevious():moves the cursor to the preevious row in the result set, returns false if the cursor is past the first row.</li><li>boolean moveToLast():moves the cursor to the lase row in the result set, returns false if the result set is empty.</li></ol> there are also some useful methods to check the position of a cursor: boolean isAfterLast(), isBeforeFirst, isFirst,isLast and isNull(columnIndex). also if you have a result set of only one row and you need to retreive values of certain columns, you can do it like this: <pre class="brush:java">public int GetDeptID(String Dept) { SQLiteDatabase db=this.getReadableDatabase(); Cursor c=db.query(deptTable, new String[]{colDeptID+" as _id",colDeptName},colDeptName+"=?", new String[]{Dept}, null, null, null); //Cursor c=db.rawQuery("SELECT "+colDeptID+" as _id FROM "+deptTable+" WHERE "+colDeptName+"=?", new String []{Dept}); c.moveToFirst(); return c.getInt(c.getColumnIndex("_id")); } </pre> we have Cursor.getColumnIndex(String ColumnName) to get the index of a column. then to get the value of a certain column we have Cursor.getInt(int ColumnIndex) method. also there are getShort,getString,getDouble, getBlob to return the value as a byte array. it's a good practice to close() the cursor after using it. Download a sample application on using database in Android from <a href="http://uploading.com/files/e67f2719/Database%2Bdemo.rar/">here</a>

Android default Database engine is Lite. SQLite is a lightweight transactional database engine that occupies small amout of disk storage and...

Using Android SlidingDrawer

Remeber Android's old versions' (prior to 2.2) launcher screen where we had a sliding pane at the bottom that when dragged upwards displays the applications menu of the phone, that is called the SlidingDrawer control. <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/SlidingDrawer/slidingdrawer1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" qx="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/SlidingDrawer/slidingdrawer1.jpg" width="320" /></a></div> consider this layout: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="wrap_content" android:layout_height="wrap_content"> <SlidingDrawer android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/drawer" android:handle="@+id/handle" android:content="@+id/content" > <ImageView android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/handle" android:src="@drawable/tray_handle_normal" /> <LinearLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" android:id="@+id/content" > <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="This is some text" android:id="@+id/txt" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Click Me" android:id="@+id/btn" android:onClick="ClickHandler" /> </LinearLayout> </SlidingDrawer> </FrameLayout> </pre> when the SlidingDrawer is pressed it looks like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/SlidingDrawer/slidingdrawer2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" qx="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/SlidingDrawer/slidingdrawer2.jpg" width="229" /></a></div> the SlidingDrawer is a container that when dragged or pressed shows/hides its contents. As the SlidingDrawer displays one content at a time, it must be declared within <a href="http://android-pro.blogspot.com/2010/02/frame-layout.html">FrameLayout</a> the SlidingDrawer has two key properties: android:handle: specifies the id of the control that acts as the handle. android:content: specifies the id of the view that acts as content of the SlidingDrawer, most times will be a container. you can open/close the drawer from the code like this: <pre class="brush:java">if(drawer.isOpened()) { drawer.close(); btnToggle.setText("Open"); } else { drawer.open(); btnToggle.setText("Close"); } </pre> you can open/close the drawer with animation using these methods instead <pre class="brush:java">drawer.animateClose(); drawer.animateOpen(); </pre> or you can handle the open/close operations automatically using toggle method: <pre class="brush:java">drawer.toggle(); drawer.animateToggle(); </pre> you can lock/unlock the SlidingDrawer to enable/disable dragging or clicking of the drawer using these methods: <pre class="brush:java">drawer.lock(); drawer.unlock(); </pre> Responding to SlidingDrawer Events: SlidingDrawer has three key callbacks: <ol><li>when the drawer is open, handled by implementing OnDrawerOpenListener.</li><li>when the drawer is close, handled by implementing OnDrawerCloseListener.</li><li>when the drawer is close, handled by implementing OnDrawerScroll Listener.</li></ol> <pre class="brush:java">drawer.setOnDrawerOpenListener(new OnDrawerOpenListener() { @Override public void onDrawerOpened() { // TODO Auto-generated method stub TextView txtStatus=(TextView)findViewById(R.id.txtStatus); txtStatus.setText("Opened"); ImageView view=(ImageView)drawer.getHandle(); view.setImageResource(R.drawable.tray_handle_selected); } }); drawer.setOnDrawerCloseListener(new OnDrawerCloseListener() { @Override public void onDrawerClosed() { // TODO Auto-generated method stub TextView txtStatus=(TextView)findViewById(R.id.txtStatus); txtStatus.setText("Closed"); ImageView view=(ImageView)drawer.getHandle(); view.setImageResource(R.drawable.tray_handle_normal); } }); drawer.setOnDrawerScrollListener(new OnDrawerScrollListener() { @Override public void onScrollStarted() { // TODO Auto-generated method stub TextView txtStatus=(TextView)findViewById(R.id.txtStatus); txtStatus.setText("Scroll start"); } @Override public void onScrollEnded() { // TODO Auto-generated method stub TextView txtStatus=(TextView)findViewById(R.id.txtStatus); txtStatus.setText("Scroll end"); } }); </pre> Notes: <ul><li>you can make the drawer appear horizontally from right to left by setting the android:orientation property to horizontal in the xml file.</li><li>you can find images used as a source for the handler from this site: <a href="http://www.netmite.com/android/mydroid/1.0/packages/apps/Phone/res/drawable-finger/">http://www.netmite.com/android/mydroid/1.0/packages/apps/Phone/res/drawable-finger/</a>  I used tray_handle_normal.9.png and tray_handle_selected.9.png</li></ul>

Remeber Android's old versions' (prior to 2.2) launcher screen where we had a sliding pane at the bottom that when dragged upwards d...

Using View Flipper in Android

Suppose you want to display a news bar in your activity. this news bar displays a single news item at a time then flips and shows next item and so on, then your choice would be Android's ViewFlipper. ViewFlipper inherits from <a href="http://android-pro.blogspot.com/2010/02/frame-layout.html">frame layout</a>, so it displays a single view at a time. consider this layout: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Flip" android:id="@+id/btn" android:onClick="ClickHandler" /> <ViewFlipper android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/flip" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Item1" /> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Item2" /> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Item3" /> </ViewFlipper> </LinearLayout> </pre>just a ViewFlipper container that contains three text views <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/Flipping/flip1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" qx="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/Flipping/flip1.png" width="225" /></a></div> now we want to flip the views when the button is clicked <pre class="brush:java">public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); btn=(Button)findViewById(R.id.btn); flip=(ViewFlipper)findViewById(R.id.flip); } public void ClickHandler(View v) { flip.showNext(); } </pre> if we want to flip in reverese direction we could use flip.showPrevious() instead we can add animations to the child views when they appear or disappear: <pre class="brush:java">@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); btn=(Button)findViewById(R.id.btn); flip=(ViewFlipper)findViewById(R.id.flip); //when a view is displayed flip.setInAnimation(this,android.R.anim.fade_in); //when a view disappears flip.setOutAnimation(this, android.R.anim.fade_out); } </pre> we can also set the ViewFlipper to flip views automatically when the button is clicked: <pre class="brush:java">public void ClickHandler(View v) { //specify flipping interval flip.setFlipInterval(1000); flip.startFlipping(); } </pre> we can stop the flipping by calling flip.stopFlipping(); method. or we can set the flipper to flip autommatically when the activity starts <pre class="brush:java">public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); btn=(Button)findViewById(R.id.btn); flip=(ViewFlipper)findViewById(R.id.flip); flip.setInAnimation(this,android.R.anim.fade_in); flip.setOutAnimation(this, android.R.anim.fade_out); flip.setFlipInterval(1000); flip.setAutoStart(true); } </pre>

Suppose you want to display a news bar in your activity. this news bar displays a single news item at a time then flips and shows next item ...

Currency Converter v1.0 released on Slide ME

Currency Converter v1.0 is released and is available at this location: the application provides real time currency convertion for more than...

Using Alerts in Android

In a previuos post we saw how to display a popup message using Toasts. Toasts are just notification messages involving no interaction from the user. another way to show interactive messages is to use Alerts. alerts act as MessageBox or JOptionPane in J2SE. they have buttons that can be used to take decisions. Creating Alerts let's check this example to create an alert and show it: <pre class="brush:java">//declared as final to be able to reference it in inner class declartations of the handlers final AlertDialog.Builder builder=new AlertDialog.Builder(this); builder.setTitle("Alert Dialog"); builder.setMessage("This is the alert's body"); builder.setIcon(android.R.drawable.ic_dialog_alert); builder.setPositiveButton("OK", new OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { TextView txt=(TextView)findViewById(R.id.txt); txt.setText("You clicked Ok"); } }); builder.setNegativeButton("Cancel", new OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub TextView txt=(TextView)findViewById(R.id.txt); txt.setText("You clicked Cancel"); } }); builder.setNeutralButton("Do something", new OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub TextView txt=(TextView)findViewById(R.id.txt); txt.setText("Neutral Button Clicked"); AlertDialog ad=builder.create(); ad.cancel(); } }); builder.setOnCancelListener(new OnCancelListener() { @Override public void onCancel(DialogInterface dialog) { // TODO Auto-generated method stub TextView txt=(TextView)findViewById(R.id.txt); txt.setText(txt.getText()+" the cancel listner invoked"); } }); builder.show(); </pre> the previous code displays the following Alert <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/Alerts/alerts1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" ox="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/Alerts/alerts1.png" width="225" /></a></div> the code may look bulky but it's very simple. first we create an instance of AlertDialog.Builder. we use the builder object to construct the AlertDialog object. we specify the title and the icon of the alert. then the text to display in the body of the message. the AlertDialog can display up to three buttons: positive button: represents the OK button. Negative button: represents the cancel button. Neutral button: represents a button to perform another functionality other than ok or cancel. note that there are no restrictions on the use of the three buttons, they can perform the same functionality the difference is just in logical meaning. but the three buttons cause the Alert dialog to dismiss. we then specify the text and the click handler of each button. in the neatral button click handler we added the lines AlertDialog ad=builder.create(); and ad.cancel();. the firt line gets a reference to the current dialog created by the builder to provide additional functionality such as invoking cancel() method. the cancel method raises the onCancel callbcak method. we could have replaced the previous code with the following: <pre class="brush:java">AlertDialog ad=builder.create(); ad.setMessage(message); ad.setIcon(icon); ad.setMessage(message); ad.setButton(text, listener); . . . </pre> Displaying Custom Views: alerts can display complex views rather than simple text messages. create an xml layout file called alertview.xml like this: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/toastView" android:background="#DAAA" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Hello alerts" android:textColor="#000" /> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/txtDate" android:textColor="#000" /> <Button android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/btnAlert" android:text="Click" /> </LinearLayout> </pre> to display this view as the alert view we do it like this: <pre class="brush:java">View bodyView=getLayoutInflater().inflate(R.layout.alertview, (ViewGroup)findViewById(R.id.toastView)); TextView txtDate=(TextView)bodyView.findViewById(R.id.txtDate); txtDate.setText(Calendar.getInstance().getTime().toLocaleString()); Button btnAlert=(Button)bodyView.findViewById(R.id.btnAlert); btnAlert.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub TextView txtDate=(TextView)bodyView.findViewById(R.id.txtDate); txtDate.setText(Calendar.getInstance().getTime().toLocaleString()); TextView txt=(TextView)findViewById(R.id.txt); txt.setText(Calendar.getInstance().getTime().toLocaleString()); } }); builder.setView(bodyView); . . . </pre> what is interesting in this approach is that the alert is fully interactive, by clicking the button you can change the value of any view in the alert or in the activity. you can also set the title of hte alert to be a custom view via builder.setCustomTitle(View v) method in the same way described above. Displaying an alert of items: alerts can display a list of items from which the user selects from like this: <pre class="brush:java">final String [] items=new String []{"Item 1","Item 2","Item 3","Item 4"}; AlertDialog.Builder builder=new AlertDialog.Builder(this); builder.setTitle("Items alert"); builder.setItems(items, new OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub TextView txt=(TextView)findViewById(R.id.txt); txt.setText(items[which]); } }); builder.show(); </pre>this will display an alert like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/Alerts/alerts2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" ox="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/September/Alerts/alerts2.png" width="226" /></a></div> notice that we do not have to specify any buttons because when the user clicks on any item the alert will be dismissed. if the list items are in an Adapter we can achieve the same result using builder.setAdapter(Adapter ad,OnClickListener listner) method: <pre class="brush:java">final String [] items=new String []{"Item 1","Item 2","Item 3","Item 4"}; ArrayAdapter<string> arr=new ArrayAdapter<string>(this, android.R.layout.select_dialog_item,items); AlertDialog.Builder builder=new AlertDialog.Builder(this); builder.setTitle("Adapter alert"); builder.setAdapter(arr, new OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub TextView txt=(TextView)findViewById(R.id.txt); txt.setText(items[which]); } }); </pre> or if the items are returned from a database in a cursor we can use builder.setCursor(Cursor cursor, OnClickListener listner, String labelColumn) Displaying alerts with items with choices: we can add items to the alert with choices whether they are single choice (Radio buttons) or multiple choices (Check boxes). to display single choice items: <pre class="brush:java">final String [] items=new String []{"Item 1","Item 2","Item 3","Item 4"}; AlertDialog.Builder builder=new AlertDialog.Builder(this); builder.setTitle("List alert"); builder.setSingleChoiceItems(items, 0, new OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub TextView txt=(TextView)findViewById(R.id.txt); txt.setText(items[which]); } }); builder.setPositiveButton("OK", new OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub } }); builder.show(); </pre> the second parameter of setSingleChoiceItems is an integer specifying the index of the selected item notice that we added a postive button that when clicked dismisses the alert cause unlike the regular items list the alert won't be dismissed when an item is selected. the builder.setSingleChoiceItems method has other overloads that can accept an Adapter or a Cursor as parameters that hold the items to be displayed to display multiple choice items: <pre class="brush:java">final String [] items=new String []{"Item 1","Item 2","Item 3","Item 4"}; AlertDialog.Builder builder=new AlertDialog.Builder(this); builder.setTitle("List alert"); builder.setMultiChoiceItems(items, null, new OnMultiChoiceClickListener() { @Override public void onClick(DialogInterface dialog, int which, boolean isChecked) { // TODO Auto-generated method stub TextView txt=(TextView)findViewById(R.id.txt); txt.setText(txt.getText()+" "+items[which]); } }); builder.setPositiveButton("OK", new OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { // TODO Auto-generated method stub } }); builder.show(); </pre> the second parameter of setMultiChoiceItems is an array of boolean values specifying which items are set selected. if you want no items to be selected then set it to null, otherwise specify an array with the same length of the items with boolean values indicating which item is selected and which is not like this: <pre class="brush:java">new boolean[] {true,false,...} </pre> works in the fashion as single items choice except that the selection here is multiple. download a demo applications on alerts from <a href="http://uploading.com/files/787127a9/Alerts%2BDemo.rar/">here</a>

In a previuos post we saw how to display a popup message using Toasts . Toasts are just notification messages involving no interaction from ...

Android popup messages using Toast

In Android you can display pop up messages that lasts for a certain duration and then disappears-using the Toast class. Toast is a transient message that appears and disappears without any interaction from the user and with no notification to the program that it disappeared. the Toast can display a simple text message or a complex view. Displaying simple text: to display a simple toast that displays a text message we use the following code: <pre class="brush:java">Toast toast=Toast.makeText(this, "Hello toast", 2000); toast.setGravity(Gravity.TOP, -30, 50); toast.show(); </pre> we create the toast using the static Toast.makeText(Context con,String message, int duration) method to create a toast in the current context to display a text message for a duration specified in milli seconds or we can use the constant values Toast.LENGTH_SHORT to display for a short duration or Toast.LENGTH_LONG for longer duration. The toast by default appears in the center of the screen, you can change the default position by specifying the Gravity and the X and Y offsets. finally we call the Show() method to display the toast. the previous toast will be like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Toasts/toast1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" ox="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Toasts/toast1.png" width="225" /></a></div> Displaying complex views: Toasts can also display complex views. this is done like this: First: create a layout xml file in res/layout directory. the file must be named toast_layout.xml. <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/toastView" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Hello toast" android:textColor="#000" /> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/txtDate" android:textColor="#000" /> </LinearLayout> </pre> then from the code <pre class="brush:java">Toast toast=new Toast(this); LayoutInflater inflater=this.getLayoutInflater(); View toastView=inflater.inflate(R.layout.toast_layout, (ViewGroup)findViewById(R.id.toastView)); TextView txtDate=(TextView)toastView.findViewById(R.id.txtDate); txtDate.setText("toast appeared at "+Calendar.getInstance().getTime().toLocaleString()); toast.setGravity(Gravity.CENTER, 0, 0); toast.setView(toastView); toast.show(); </pre> the toast will be like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Toasts/toast2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" ox="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Toasts/toast2.png" width="226" /></a></div>Notes: <ul><li>In the toast_layout.xml width, if you put any buttons or any control that has a callback, it would appear disabled and the user cannot interact with it.</li><li>The toast can be created in two ways: by calling Toast.makeText method or by specifyinga view via setView method. when you want to display a simple text use the first one otherwise use the second. if you try to interchange or combie between the two methods an exception will be thrown.</li></ul>

In Android you can display pop up messages that lasts for a certain duration and then disappears-using the Toast class. Toast is a transient...

Using Themes and Styles in Android

<div dir="ltr" style="text-align: left;" trbidi="on">In web design we have the concept of Styles and Themes. Styles like Cascading Style Sheets (CSS) define the values of the web controls attributes such as width, heigth, font color, background and so on. A style can be applied on several controls in several web pages. Themes are used to group a set of styles to be applied on the whole web application. Themes (or sometimes skins) define the look of all control within the application. Android introduces similar concepts by using Styles and Themes. A Style can be applied to views individually while a Theme is applied to a whole activity. Styles: Styles are defined as xml resources files in res/values directory of your project. consider this definition of a TextView: <pre class="brush:xml"><TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:textColor="#FFF" android:typeface="monospace" android:text="First Text View" android:background="#00F" /> </pre> this defines a text view with width and height equal to wrap_content, white font color, font type "monospace" and blue back ground. if we want to have the same results using a style: we first create a xml file (call it styles.xml) in res/values directory and it would be like this: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <resources> <style name="BlueLabel"> <item name="android:layout_width">fill_parent</item> <item name="android:layout_height">wrap_content</item> <item name="android:typeface">monospace</item> <item name="android:background">#00F</item> <item name="android:textColor">#FFF</item> </style> </resources> </pre> then redefine the TextView like this: <pre class="brush:xml"><TextView android:text="First Text View" style="@style/BlueLabel" / > </pre> and you will receive the same results. the attributes in the <item>tag can be any layout property. Inheriting Styles: Styles in Android has an interesting feature which is the ability to inherit styles in a fashion similar to that in CSS. consider this example: we have a style for a button like this: <pre class="brush:xml"><style name="ButtonStyle"> <item name="android:layout_width">wrap_content</item> <item name="android:layout_height">wrap_content</item> <item name="android:textSize">15px</item> <item name="android:typeface">serif</item> </style> </pre> the button will appear like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Styles/styles1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" ox="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Styles/styles1.png" width="224" /></a></div> we can make this style inherit from BlueLabel defined previously by adding the parent attribute to the <style*gt; tag: <pre class="brush:xml"><style name="ButtonStyle" parent="BlueLabel"> </pre>then the button will be like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Styles/styles2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" ox="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Styles/styles2.png" width="226" /></a></div>the button inherited the background color from the parent style. another interesting feature in styles inheritance is the ability to inherit from the platform built-in styles defined in the android.R.style namespace. to know more about the platform styles check this <a href="http://android.git.kernel.org/?p=platform/frameworks/base.git;a=blob;f=core/res/res/values/styles.xml;h=d7b654e49809cb97a35682754b1394af5c8bc88b;hb=HEAD">link</a> or you can type in your editor (Eclipse) android.R.style and let the intelli-sense list you the complete list of platform styles, if you want to use them in your xml just replace the undrscores with a period like this: Widget_Button becomes @android:style/Widget.Button. In the previous button style example we will set the parent of the style to be @android:style/Widget.Button.Small and the button will be like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Styles/styles3.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" ox="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Styles/styles3.png" width="225" /></a></div> Note: if you apply a style to a ViewGroup widget, it's child widgets will not inherit that style. Using Themes you can apply styles as themes on an activity level or application level. if you apply a theme on an activity level then all widgets within that activity will inherit from that theme. to do so, open the AndroidManifest.xml and go the <activity> tag and add the android:theme attribute: <pre class="brush:xml"><activity android:name=".StylesDemo" android:label="@string/app_name" android:theme="@style/BlueLabel"> </pre> to apply a theme on the application level so that the style will be applied to all activities within your application, open the AndroidManifest.xml and go the <application> tag and add the android:theme attribute: <pre class="brush:xml"><application android:icon="@drawable/icon" android:label="@string/app_name" android:theme="@style/BlueLabel"> </pre> to set the theme of an activity programmatically call this line in the onCreate method <pre class="brush:java">this.setTheme(R.style.BlueLabel); </pre></div>

In web design we have the concept of Styles and Themes. Styles like Cascading Style Sheets (CSS) define the values of the web controls attri...

Android Error: Error generating final archive: Debug certificate expired on …

One day I opened eclipse to start a new android application, after creating the project and trying to run it I received the following error: [2010-08-27 15:32:04 – (Project Name)] Error generating final archive: Debug certificate expired on 7/30/10 10:42 PM! After searching I found this link which suggests the solution: <a href="http://www.androidian.de/?p=940">http://www.androidian.de/?p=940</a>. The problem comes from the fact that Android required the applications to be signed even in the debug mode. So it uses a keystore file called debug.keystore to providde keys for signing applications in debug mode. This key store file has a validity period by default 365 days from its creation date. The First Solution: Navigate to the .android folder in your home directory “~/.android” (Linux,Mac OS) or c:\Documents and Settings\[User Name]\.android in windows XP or C:\Users\.android in windows Vista or Windows 7, and delete debug.keystore file. Then go to eclipse clean the project, this will create a new debug.keystore file with default validity period 365 days. The Second Solution: Create a new default.keystore file with custom validity period (say 1000 days). <div></div><div></div><ol><li>Navigate to the .android folder.</li><li>Delete the old default.keystore file.</li><li>We will use JDK Keytool.exe to generate the new key file. It is found in C:\Program Files\Java\jre6\bin in windows or inside the Java\jre6\bin folder in Mac OS or Linux.</li><li>Open the terminal app in Mac OS or Linux or the command prompt and navigate to keytool.exe directory.</li><li>Run the following command: keytool -genkey -keypass android -keystore debug.keystore -alias androiddebugkey -storepass android -validity 1000 -dname “CN=Android Debug,O=Android,C=US”</li><li>This will generate a new default.keystore file with validity period 1000 days.</li><li>Copy the generated file to the .android folder, go to eclipse and clean projects and it should work.</li></ol>The above command has the following options: <ul><li>genkey: generates a key pair.</li><li>keystore <Key Store Name>: the name of the key store file.</li><li>alias <alias name>: an alias for the key store. If the alias name is more than 8 characters the first 8 only are used.</li><li>storepass <password>: the password for the key.</li><li>validity <Validty Period>: the validity period for the key in days.</li><li>dname <name>: A Distinguished Name that describes who created the key. The value is used as the issuer and subject fields in the self-signed certificate.</li></ul><div></div>

One day I opened eclipse to start a new android application, after creating the project and trying to run it I received the following error:...

iPhone-Like Tab bar in Android

In a previous post we saw how to use the TabHost to create tabs in Android applications. Also we noticed that the Tabs in Android appear at the top of the activity. but what if we want to give the tabs the look of the iPhone Tab Bar ? this is possible by wrapping the TabWidget and the FrameLayout in a RelativeLayout container and adding android:layout_alignParentBottom="true" attribute to the TabWidget just like this: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <TabHost android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@android:id/tabhost" xmlns:android="http://schemas.android.com/apk/res/android" > <RelativeLayout android:layout_width="fill_parent" android:layout_height="fill_parent" > <TabWidget android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@android:id/tabs" android:layout_alignParentBottom="true" /> <FrameLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@android:id/tabcontent" > </FrameLayout> </RelativeLayout> </TabHost> </pre> <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs6.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" bx="true" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs6.jpg" width="224" /></a></div>

In a previous post we saw how to use the TabHost to create tabs in Android applications. Also we noticed that the Tabs in Android appear at ...

Tabbed Applications in Android

Some times we want to wrap multiple views in a single window and navigate throught them with a Tab Container. this can be done in Android using TabHost control There are two ways to use a TabHost application in Android: <ol><li>Using the TabHost to navigate through multiple views within the same activity.</li><li>Using the TabHost to navigate through Actual multiple Activities using intents.</li></ol>we will explain both ways through this tutorial Anatomy of Tabbed Application An activity with a TabHost may look like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" bx="true" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs1.jpg" width="258" /></a></div> The Activity consists of: <ol><li>A TabHost: the root element of the layout.</li><li>The TabHost wraps a TabWidget which represents the tab bar.</li><li>The TabHost wraps a FrameLayout which wraps the contents of each tab.</li></ol>There are some rules that we must stick to when using a Tabbed activity: <ol><li>If the activity is of type TabActivity [optional] then the TabHost must have the id @android:id/tabhost.</li><li>The TabWidget must have the id @android:id/tabs.</li><li>The FrameLayout must have the id @android:id/tabcontent.</li></ol>no let's see an exaple to an activity with multiple tabs: this is the layout <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <TabHost android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/tabHost" xmlns:android="http://schemas.android.com/apk/res/android" > <TabWidget android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@android:id/tabs" /> <FrameLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@android:id/tabcontent" > <LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/tab1" android:orientation="vertical" android:paddingTop="60px" > <TextView android:layout_width="fill_parent" android:layout_height="100px" android:text="This is tab1" android:id="@+id/txt1" /> </LinearLayout> <LinearLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/tab2" android:orientation="vertical" android:paddingTop="60px" > <TextView android:layout_width="fill_parent" android:layout_height="100px" android:text="This is tab 2" android:id="@+id/txt2" /> </LinearLayout> <LinearLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/tab3" android:orientation="vertical" android:paddingTop="60px" > <TextView android:layout_width="fill_parent" android:layout_height="100px" android:text="This is tab 3" android:id="@+id/txt3" /> </LinearLayout> </FrameLayout> </TabHost> </pre> then in the code of our activity <pre class="brush:java">public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); TabHost tabHost=(TabHost)findViewById(R.id.tabHost); tabHost.setup(); TabSpec spec1=tabHost.newTabSpec("Tab 1"); spec1.setContent(R.id.tab1); spec1.setIndicator("Tab 1"); TabSpec spec2=tabHost.newTabSpec("Tab 2"); spec2.setIndicator("Tab 2"); spec2.setContent(R.id.tab2); TabSpec spec3=tabHost.newTabSpec("Tab 3"); spec3.setIndicator("Tab 3"); spec3.setContent(R.id.tab3); tabHost.addTab(spec1); tabHost.addTab(spec2); tabHost.addTab(spec3); } </pre> is going to look like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" bx="true" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs2.jpg" width="225" /></a></div> <ol><li>We create tabs using TabSpecs class.</li><li>We set the title of each tab using TabSpecs.setIndicator() method.</li><li>We set the content of each tab using TabSpecs.setContent() method.</li><li>if you use TabActivity to as a base class to your activity, you do not need to call TabHost.Setup() method.</li></ol>We can add an icon to the title of the tab like this: <pre class="brush:java">TabSpec spec1=tabHost.newTabSpec("Tab 1"); spec1.setContent(R.id.tab1); spec1.setIndicator("Tab 1",getResources().getDrawable(R.drawable.flash)); TabSpec spec2=tabHost.newTabSpec("Tab 2"); spec2.setIndicator("Tab 2",getResources().getDrawable(R.drawable.sun)); spec2.setContent(R.id.tab2); TabSpec spec3=tabHost.newTabSpec("Tab 3"); spec3.setIndicator("Tab 3",getResources().getDrawable(R.drawable.chart)); spec3.setContent(R.id.tab3); </pre> it will look like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" bx="true" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs3.jpg" width="227" /></a></div> we can also specify the indicator to be a view: <pre class="brush:java">TabSpec spec1=tabHost.newTabSpec("Tab 1"); spec1.setContent(R.id.tab1); TextView txt=new TextView(this); txt.setText("Tab 1"); txt.setBackgroundColor(Color.RED); spec1.setIndicator(txt); </pre> Setting the content of tabs: we saw how to set the contents of tabs by specifying multiple layout resources to be displayed within the same activity. what If we have multiple Activities in our application and we want to navigate between them using tabs ? in this case we will have one activity as the root activity of the application. this activity will have the TabHost and will navigate to other activities using Intents. Note: the root activity must inherit from TabActivity. the root activity will have layout file like this: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <TabHost android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@android:id/tabhost" xmlns:android="http://schemas.android.com/apk/res/android" > <TabWidget android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@android:id/tabs" /> <FrameLayout android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@android:id/tabcontent" > </FrameLayout> </TabHost> </pre> the other activities will have a simple layout consisting of a TextView. now to the code of the roor activity <pre class="brush:java">public class TabDemo extends TabActivity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); TabHost tabHost=getTabHost(); // no need to call TabHost.Setup() //First Tab TabSpec spec1=tabHost.newTabSpec("Tab 1"); spec1.setIndicator("Tab 1",getResources().getDrawable(R.drawable.sun)); Intent in1=new Intent(this, Act1.class); spec1.setContent(in1); TabSpec spec2=tabHost.newTabSpec("Tab 2"); spec2.setIndicator("Tab 2",getResources().getDrawable(R.drawable.chart)); Intent in2=new Intent(this,Act2.class); spec2.setContent(in2); tabHost.addTab(spec2); tabHost.addTab(spec3); } } </pre> and the activity will look like this <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs4.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" bx="true" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs4.jpg" width="224" /></a></div> Adding tabs at run-time: we can add tabs to TabHost at run-time using TabSpec.setContent(TabContentFactory) method. the TabContentFactory is an interface that requires the implementation of a callback method createTabContent(String tag) which returns the view to be added to the content of the tab. so in the last example if we changed code that adds the content of the second tab to this: <pre class="brush:java">TabSpec spec1=tabHost.newTabSpec("Tab 1"); spec1.setIndicator("Tab 1",getResources().getDrawable(R.drawable.sun)); spec1.setContent(new TabContentFactory() { @Override public View createTabContent(String tag) { // TODO Auto-generated method stub return (new AnalogClock(TabDemo.this)); } }); </pre> the activity will look like this <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs5.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" bx="true" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/August/Tabs/Tabs5.jpg" width="225" /></a></div>

Some times we want to wrap multiple views in a single window and navigate throught them with a Tab Container. this can be done in Android us...

Android Simple Image Gallery

In this post we are going to use the <a href="http://android-pro.blogspot.com/2010/07/android-gallery-control.html">gallery</a> control t construct a simple image gallery. the layout is like the previous <a href="http://android-pro.blogspot.com/2010/07/android-gallery-control.html">post</a>. remeber that the Gallery control is populated by an adapter, so we will create a custom adapter that contains ImageViews to display the images. our custom adapter must inherit from BaseAdapter class <pre class="brush:java">package mina.android.GalleryDemo; import java.util.ArrayList; import java.util.List; import android.content.Context; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.ImageView; public class ImageAdapter extends BaseAdapter { Context Con; //array to hold the values of image resources int [] Resources; List<imageview> views; public ImageAdapter(Context con,int[] resources) { Con=con; Resources=resources; views=new ArrayList<imageview>(resources.length); } @Override public int getCount() { // TODO Auto-generated method stub return Resources.length; } @Override public Object getItem(int position) { // TODO Auto-generated method stub return views.get(position); //return position; } @Override public long getItemId(int position) { // TODO Auto-generated method stub //return views.get(position).getId(); return position; } @Override public View getView(int position, View convertView, ViewGroup parent) { // TODO Auto-generated method stub ImageView img=new ImageView(Con); img.setImageResource(Resources[position]); views.add(img); return img; } } </pre> then in our activity onCreate Method: <pre class="brush:java">int []res=new int[]{R.drawable.wc,R.drawable.wc2,R.drawable.wc3,R.drawable.wc4,R.drawable.wc5}; ItemsInGallery=res.length; ImageAdapter imgAdapter=new ImageAdapter(this, res); gallery.setAdapter(imgAdapter); </pre> and that was our simple Image gallery. download the application from <a href="http://uploading.com/files/a9camd4a/Gallery%2BDemo2.rar/">here</a>

In this post we are going to use the gallery control t construct a simple image gallery. the layout is like the previous post . remeber tha...

Android Gallery Control

In Android the Gallery control is a selection control that displays items in a horizontal gallery. the items in the gallery appear beside each other. they can appear separated by a pre-defined space. remember that there is a sample demo application for the gallery to download at the end of the post we can use the gallery to display String items using a simple ArrayAdapter. so let's see how to create a gallery that displays the word "Hello" in several languages: the layout: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Gallery Demo" /> <Gallery android:id="@+id/gallery" android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center_horizontal" android:spacing="100px" /> </LinearLayout> </pre> and in the OnCreate method <pre class="brush:java">@Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); gallery=(Gallery)findViewById(R.id.gallery); //String array holding the values String [] text=new String[]{"Hello","Hi","Alloha","Bonjour","Hallo","¡Hola"}; //Array adapter to display our values in the gallery control ArrayAdapter<string> arr=new ArrayAdapter<string>(this, android.R.layout.simple_gallery_item, text); gallery.setAdapter(arr); } </pre> the gallery will be like this <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/July/Gallery%20Control/gallery.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" hw="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/July/Gallery%20Control/gallery.jpg" width="224" /></a></div> we can increse the spacing between the items by increasing the value of android:spacing property. we can display a scroll bar to indicate the position of the current selected item in the gallery like this: <pre class="brush:xml"><Gallery android:id="@+id/gallery" android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center_horizontal" android:spacing="100px" android:scrollbars="horizontal" android:scrollbarFadeDuration="0" android:scrollX="100px" /> </pre> <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/July/Gallery%20Control/gallery2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" hw="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/July/Gallery%20Control/gallery2.jpg" width="223" /></a></div> setting the android:scrollbarFadeDuration="0" makes the scroll bar always visible. The android:scrollX property defines the initial scroll offset of the scroll bar which is the initial distance that the gallery is scrolled for. Handling Gallery Events since the gallery is a selction Control (a adapter view) so it can register a OnItemSelectedListener to handle the selection of items within the gallery. <pre class="brush:java">final String [] text=new String[]{"Hello","Hi","Alloha","Bonjour","Hallo","¡Hola"}; gallery.setOnItemSelectedListener(new OnItemSelectedListener() { @Override public void onItemSelected(AdapterView parent, View view, int position, long id) { // TODO Auto-generated method stub TextView txt=(TextView)findViewById(R.id.txt); txt.setText(text[position].toString()); } @Override public void onNothingSelected(AdapterView parent) { // TODO Auto-generated method stub } }); </pre> now the final step is to add two navigation buttons: Next and Previous to navigate throught the items in the gallery. the layout is gonna be like this: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Gallery Demo" android:id="@+id/txt" /> <Gallery android:id="@+id/gallery" android:layout_width="fill_parent" android:layout_height="wrap_content" android:gravity="center_horizontal" android:spacing="100px" android:scrollbars="horizontal" android:scrollbarFadeDuration="0" android:scrollX="100px" /> <LinearLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="horizontal" android:layout_marginTop="5px" > <Button android:text="Previous" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/btnPrev" android:onClick="onClick" /> <Button android:text="Next" android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/btnNext" android:onClick="onClick" /> </LinearLayout> </LinearLayout> </pre><div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/July/Gallery%20Control/gallery3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" hw="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/July/Gallery%20Control/gallery3.jpg" width="226" /></a></div> now in order to keep track of the index of the currently selected item we need to define two variables <pre class="brush:java">//Variable to store the number of items in the gallery int ItemsInGallery=0; int CurrentIndex=0; </pre> and the navigation buttons click handlers: <pre class="brush:java">@Override public void onClick(View v) { // TODO Auto-generated method stub switch(v.getId()) { case R.id.btnNext: //Increase the index CurrentIndex++; //if reached the end of the gallery, then start from the first item if(CurrentIndex>ItemsInGallery-1) CurrentIndex=0; gallery.setSelection(CurrentIndex,true); txt.setText(String.valueOf(CurrentIndex)); break; case R.id.btnPrev: //Decrease the index CurrentIndex=CurrentIndex-1; //If reached the first item, then return to the last item in the gallery if(CurrentIndex<0) CurrentIndex=ItemsInGallery-1; gallery.setSelection(CurrentIndex,true); txt.setText(String.valueOf(CurrentIndex)); break; } } </pre>you can download a sample program from <a href="http://uploading.com/files/m41mc713/Gallery%2BDemo.rar/">here</a>

In Android the Gallery control is a selection control that displays items in a horizontal gallery. the items in the gallery appear beside ea...

How to rotate the Android Emulator ?

To rotate the Android Emulator, just disable the Num Lock key and and use the 7 and the 9 in the num pad to rotate the emulator and chang...

Android Intents: Part3: Intent Filters

<div dir="ltr" style="text-align: left;" trbidi="on">Android components like activities can also serve implicit intents. but to do so they have to filter all implicit intents in order to serve only the intents they desire to serve. this is done using intent filters. Suppose you want to create an activity that acts as the default dialer activity. You must associate an intent filter with this activity in order to that this activity serve the dial intents only. Let's demonstrate a simple example which is creating an application with one activity that we want to make it a dialer activity. Create a new android project, create an activity and name it Dialer. In the AndroidManifest.xml file of this application add the following to the Dialer activity: <pre><intent-filter android:priority="100" > <action android:name="android.intent.action.DIAL" /> <category android:name="android.intent.category.DEFAULT" /> <data android:scheme="tel"/> </intent-filter></pre>to become: <pre class="brush:xml"><activity android:name=".Dialer" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> <intent-filter android:priority="100" > <action android:name="android.intent.action.DIAL" /> <category android:name="android.intent.category.DEFAULT" /> <data android:scheme="tel"/> </intent-filter> </activity></pre>Now what we have done is adding an intent filter to that activity. this intent filter has the following properties: <ol><li>Action: the type of implicit intents that this activity responds to. in our case it is the dial action. higher numbers represent higher priority.</li><li>Priority: about the priority of that activity over other activities that respond to the same type of intents.</li><li>Category: Implicit intents have built-in categories. in order that an implicit intent be captured by our activity, the implicit intent category must match our activity category.</li><li>Data: adds data specification scheme to the intent filter.</li></ol>So if any other application has the following module to launch the dialer: <pre class="brush:java">Intent in=new Intent(Intent.ACTION_DIAL, Uri.parse("tel:000")); startActivity(in);</pre>The user will see the following dialog offering him/her the choice between the default dialer and our custom dialer. <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/July/Intents%203/intentfilters.bmp" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="170" l6="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/July/Intents%203/intentfilters.bmp" width="200" /></a></div></div>

Android components like activities can also serve implicit intents. but to do so they have to filter all implicit intents in order to serve ...

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