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Connecting to a web service over a Secure Sockets Layer (SSL): protocol:

<div dir="ltr" style="text-align: left;" trbidi="on">Android default HttpClinet does not support SSL connections, so if you have a secured web service, you need to connect to it via javax.net.ssl.HttpsURLConnection. if you want to call a SSL SOAP web service: <pre class="brush:java">String CallWebService(String url, String soapAction, String envelope) throws IOException { URL address=new URL(url); URLConnection connection=address.openConnection(); HttpsURLConnection post=(HttpsURLConnection)connection; post.setDoInput(true); post.setDoOutput(true); post.setRequestMethod("POST"); post.setRequestProperty("SOAPAction", soapAction); post.setRequestProperty( "Content-type", "text/xml; charset=utf-8" ); post.setRequestProperty( "Content-Length", String.valueOf(envelope.length())); post.setReadTimeout(4000); OutputStream outStream=post.getOutputStream(); Writer out=new OutputStreamWriter(outStream); out.write(envelope); out.flush(); out.close(); InputStream inStream = post.getInputStream(); BufferedInputStream in = new BufferedInputStream(inStream,4); StringBuffer buffer=new StringBuffer(); // read 4 bytes a time byte[] buffArray=new byte[4]; int c=0; while((c=in.read(buffArray))!=-1){ for(int i=0;i<c;i++) buffer.append((char)buffArray[i]); } return buffer.toString(); } </pre></div>

Android default HttpClinet does not support SSL connections, so if you have a secured web service, you need to connect to it via javax.net....

Calling SOAP Web Services with Android APIs

<div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on">One of the most common functionalities required in mobile applications is to call a web service to retrieve data. This process involves requesting the web service with parameters, receiving the response and parsing it to obtain data. Today the most common web services types are SOAP and REST. Android does not provide a built in SOAP client, there are many third party libraries that can be used, but we'll see how to call a SOAP web service with native android APIs. Requesting SOAP web service:</div>Before proceeding to the code, let's take a look at the SOAP structure: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/May/web%20service/soap_structure.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="200" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/May/web%20service/soap_structure.png" width="186" /></a></div> a soap request can be something like this: <pre class="brush:xml">POST /InStock HTTP/1.1 Host: www.example.org Content-Type: application/soap+xml; charset=utf-8 Content-Length: length SOAPAction: "http://www.w3schools.com/GetItems" <?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope" soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding"> <soap:Header> <m:Trans xmlns:m="http://www.w3schools.com/transaction/" soap:mustUnderstand="1">234 </m:Trans> </soap:Header> <soap:Body> <m:GetPrice xmlns:m="http://www.w3schools.com/prices"> <m:Item>Apples</m:Item> </m:GetPrice> </soap:Body></soap:Envelope> </pre> the SOAP request/response is sent as a SOAP Envelope which consists of a SOAP Header and a SOAP Body. <ol style="text-align: left;"><li>SOAP Header: optional component of the envelop, contains application specific information, such as authentication.</li><li>SOAP Body: the actual message sent to/received from the service.</li><li>The header can contain a SOAP Action which identifies the desired function to be called by the service.</li></ol><div>Calling the service:</div></div>to call the SOAP web service you have to do the following: First: construct the SOAP envelope manually like this: <pre class="brush:xml">String envelope="<?xml version=\"1.0\" encoding=\"utf-8\"?>"+ "<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">"+ "<soap:Body>"+ "<GetItems xmlns=\"http://tempuri.org/\">"+ "<startDate>%s</ startDate>"+ "<getAll>%s</getAll>"+ "</Items>"+ "</soap:Body>"+ "</soap:Envelope>"; </pre>where %s are place holders where you substitute request parameters in like this <pre class="brush:java">String requestEnvelope=String.format(envelope, "10-5-2011","true"); </pre> Second: call the web service like this: <pre class="brush:java">String CallWebService(String url, String soapAction, String envelope) { final DefaultHttpClient httpClient=new DefaultHttpClient(); // request parameters HttpParams params = httpClient.getParams(); HttpConnectionParams.setConnectionTimeout(params, 10000); HttpConnectionParams.setSoTimeout(params, 15000); // set parameter HttpProtocolParams.setUseExpectContinue(httpClient.getParams(), true); // POST the envelope HttpPost httppost = new HttpPost(url); // add headers httppost.setHeader("soapaction", soapAction); httppost.setHeader("Content-Type", "text/xml; charset=utf-8"); String responseString=""; try { // the entity holds the request HttpEntity entity = new StringEntity(envelope); httppost.setEntity(entity); // Response handler ResponseHandler<string> rh=new ResponseHandler<string>() { // invoked when client receives response public String handleResponse(HttpResponse response) throws ClientProtocolException, IOException { // get response entity HttpEntity entity = response.getEntity(); // read the response as byte array StringBuffer out = new StringBuffer(); byte[] b = EntityUtils.toByteArray(entity); // write the response byte array to a string buffer out.append(new String(b, 0, b.length)); return out.toString(); } }; responseString=httpClient.execute(httppost, rh); } catch (Exception e) { Log.v("exception", e.toString()); } // close the connection httpClient.getConnectionManager().shutdown(); return responseString; } </string></string></pre></div> after calling this function, you will have the response as a String, something like this: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <GetItemsResponse xmlns="http://tempuri.org/"> <GetItemsResult> <Items> <Item> <name>string</name> <description>string</ description > </iPhoneCategory> <iPhoneCategory> <name>string</name> <description>string</ description > </ Item > </Items> </GetItemsResult> </ GetItemsResponse > </soap:Body> </soap:Envelope> </pre> this response needs to be parsed to extract the data.</div></div></div></div>

One of the most common functionalities required in mobile applications is to call a web service to retrieve data. This process involves requ...

Calling REST Web Services with Android.

<div dir="ltr" style="text-align: left;" trbidi="on">Requesting REST web service:   you request REST web services by calling a URL with the parameters. like this <pre>http://example.com/resources/getitems</pre> an example of calling a REST web service: <pre class="brush:java">String callWebErvice(String serviceURL){ // http get client HttpClient client=new DefaultHttpClient(); HttpGet getRequest=new HttpGet(); try { // construct a URI object getRequest.setURI(new URI(serviceURL)); } catch (URISyntaxException e) { Log.e("URISyntaxException", e.toString()); } // buffer reader to read the response BufferedReader in=null; // the service response HttpResponse response=null; try { // execute the request response = client.execute(getRequest); } catch (ClientProtocolException e) { Log.e("ClientProtocolException", e.toString()); } catch (IOException e) { Log.e("IO exception", e.toString()); } try { in=new BufferedReader(new InputStreamReader(response.getEntity().getContent())); } catch (IllegalStateException e) { Log.e("IllegalStateException", e.toString()); } catch (IOException e) { Log.e("IO exception", e.toString()); } StringBuffer buff=new StringBuffer(""); String line=""; try { while((line=in.readLine())!=null) { buff.append(line); } } catch (IOException e) { Log.e("IO exception", e.toString()); return e.getMessage(); } try { in.close(); } catch (IOException e) { Log.e("IO exception", e.toString()); } // response, need to be parsed return buff.toString(); } </pre></div>

Requesting REST web service: you request REST web services by calling a URL with the parameters. like this http://example.com/resources/g...

Official Google Blog: Coming soon: make your phone your wallet

Using Android Preferences

<div dir="ltr" style="text-align: left;" trbidi="on">We saw before that we can persist an application's data using SQLite database. Android offers another way to store user's data through using preferences. Android preferences is a key/value entries that store data that can be specific to a certain activity or shared among all activities within the application. the data are stored in a xml file. Saving Preferences We can save preferences in three ways: <ol style="text-align: left;"><li>Preferences can be retrieved only by a single activity.</li><li>Preferences can be shared and retrieved among all activities within the application.</li><li>Preferences can be shared and retrieved through all applications on the device.</li></ol><div>Saving Activity-level preferences:</div>to save preferences that are accessed only from a single activity, we do it like this: <pre class="brush:java">SharedPreferences prefs=getPreferences(Context.MODE_PRIVATE); SharedPreferences.Editor editor=prefs.edit(); editor.putString("pref 1", "some text"); editor.commit(); </pre> we get a SharedPreferences object by calling getPreferences(int mode) method which takes an integer value as a parameter, the mode value can be one of the following: <ol style="text-align: left;"><li>Context.MODE_PRIVATE (0): a file creating mode that makes the created file only accessible by applications with the same user ID (access the file from the same application context, will desctribe later).</li><li>Context.MODE_WORLD_READABLE (1): file mode makes the file readable from other applications.</li><li>Context.MODE_WORLD_WRITEABLE (2): file mode allows other applications to write to the file.</li></ol><div>then we get an instance of SharedPreferences.Editor and write the preference value with editor.putString(String key, String value) method. shared preferences allows you to insert preferences using the following methods: <ol style="text-align: left;"><li>editor.putBoolean(String key, boolean value).</li><li>editor.putFloat(String key,float value).</li><li>editor.putInt(String key, int value).</li><li>editor.putLong(String key, long value)</li><li>editor.putString(String key, String value)</li></ol><div>then we call edit.commit() to save the preferences to the file. commit returns a boolean indicating the result of saving, true if successful and false if failed.</div><div> </div><div>Reading preferences values:</div>To read preferences values: <pre class="brush:java">SharedPreferences prefs=getPreferences(Context.MODE_PRIVATE); String val=prefs.getString("pref 1", "some text"); </pre>we use sharedpreferences.getString(String key, String defaultValue) (or get boolean/float/int) to return the value stored with a specific key or defaultValue if not found. Saving Application-level preferences: to save preferences that can be retrieved from all activities in the application we do it like this: <pre class="brush:java">SharedPreferences prefs= getSharedPreferences("demopref", Context.MODE_WORLD_READABLE); SharedPreferences.Editor editor=prefs.edit(); editor.putString("demostring", "hello"); editor.commit(); </pre> same as the code above, but the difference is that we give our preferences file a name (demopref in this case) so that other activities can reference that preferences file. Sharing preferences across applications: We can store preferences in one application and read them in another application, this is done reading the preferences file by loading them through the first application's context. let's assume we have two applications: <ol style="text-align: left;"><li>Application 1 with package name "com.mina.prefdemo".</li><li>Application2 with package name "com.mina.demoapp".</li></ol><div>If application1 creates a preferences file with the name "demopref" and inserts a String preference with the key/value "demostring/hello".</div><div> </div><div>now we access this file and value from application 2 like this: <pre class="brush:java">Context con; try { con = createPackageContext("com.minasamy.prefdemo", 0); SharedPreferences pref=con.getSharedPreferences("demopref", Context.MODE_PRIVATE); String x=pref.getString("demostring", "not found"); txt.setText(x); } catch (NameNotFoundException e) { Log.e(Tag, e.toString()); } </pre> Creating Preferences Activities: android provides another nice way of presenting and saving preferences. you can create Activities that extend PreferenceActivity. PreferenceActivity is an activity that displays a set of built-in preferences related widgets that are defined in xml file. the preference activity can be divided to several PreferenceCategory each containing a set of related preferences. The preferences widgets that Android provide are: <ol style="text-align: left;"><li>CheckBoxPreference: displays a check box widget.</li><li>EditTextPreference: displays an EditText widget to save user prefs.</li><li>RingtonePreference: displays a list with the  ringtones on the device.</li><li>ListPreference: displays a list of key/value items.</li></ol><div>each one of these preferences widgets is associated with a preference key. it's value is persisted instantly as the widget selection changes.</div><div> </div><div>we can construct our preferences screen xml (saved in res/xml directory) layout like this: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"> <PreferenceCategory android:title="Catogory one" android:summary="sample summary"> <CheckBoxPreference android:title="Enable" android:key="pref_enable" android:summary="enables a preference"/> <EditTextPreference android:summary="Edit text prefrence" android:title="Edit" android:key="pref_edit"/> </PreferenceCategory> <PreferenceCategory android:title="Category2" android:summary="sample summary"> <RingtonePreference android:key="pref_ring" android:title="Ringtones preference"/> <ListPreference android:key="pref_list" android:title="List Preference" android:dialogTitle="List Pref Dialog" android:entries="@array/pref_items" android:entryValues="@array/pref_items_values"/> </PreferenceCategory> </pre> then from our activity: <pre class="brush:java">public class PrefActivity extends PreferenceActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); addPreferencesFromResource(R.xml.prefs); } } </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/2011/May/prefs/prefs1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/May/prefs/prefs1.png" width="213" /></a></div><div class="separator" style="clear: both; text-align: center;"> </div><div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/May/prefs/prefs2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/May/prefs/prefs2.png" width="213" /></a></div><div class="separator" style="clear: both; text-align: center;"> </div><div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/May/prefs/prefs3.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/May/prefs/prefs3.png" width="213" /></a></div><div class="separator" style="clear: both; text-align: center;"> </div><div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/May/prefs/prefs4.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/May/prefs/prefs4.png" width="213" /></a></div><div class="separator" style="clear: both; text-align: center;"> </div><div class="separator" style="clear: both; text-align: center;"> </div>the ListPreference can be associated with String array resources as it's key/value entries <pre class="brush:xml"><string-array name="pref_items"> <item>Item1</item> <item>Item2</item> <item>Item3</item> <item>Item4</item> <item>Item5</item> </string-array> <string-array name="pref_items_values"> <item>1</item> <item>2</item> <item>3</item> <item>4</item> <item>5</item> </string-array> </pre> to reference the preference widgets programmatically: <pre class="brush:java">EditTextPreference pref_edit=(EditTextPreference)findPreference("pref_edit"); </pre></div></div></div></div>

We saw before that we can persist an application's data using SQLite database. Android offers another way to store user's data throu...

The Difference between Handler and AsyncTask

<div dir="ltr" style="text-align: left;" trbidi="on"> After we saw both Handlers and AsyncTasks a question may evolve: what's the difference between the two and when to use one of them over the other ? The Handler is associated with the application's main thread. it handles and schedules messages and runnables sent from background threads to the app main thread. AsyncTask provides a simple method to handle background threads in order to update the UI without blocking it by time consuming operations. The answer is that both can be used to update the UI from background threads, the difference would be in your execution scenario. You may consider using handler it you want to post delayed messages or send messages to the MessageQueue in a specific order. You may consider using AsyncTask if you want to exchange parameters (thus updating UI) between the app main thread and background thread in an easy convinient way. </div>

After we saw both Handlers and AsyncTasks a question may evolve: what's the difference between the two and when to use one of them over ...

Google to Unveil Service to Let Users Stream Their Music

Google will announce today on Google I/O 2011 it's long anticipated Cloud-based music service.

Threading in Android part 2: Async Tasks

<div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on">In the <a href="http://android-pro.blogspot.com/2011/05/threading-in-android-part-1-handlers.html/">previous post</a> we saw one way to deal with threads in Android, which is by using Handlers. In this post we'll see how to use another technique which is using AsyncTask class. AsyncTask is an abstract class that provides several methods managing the interaction between the UI thread and the background thread. it's implementation is by creating a sub class that extends AsyncTask and implementing the different protected methods it provides. Let's demonstrate how to user AsyncTask by creating a simple activity that has two buttons and a progress bar: <pre class="brush:xml"><?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <Button android:id="@+id/btn" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Show Progress" ></Button> <ProgressBar android:layout_width="fill_parent" android:layout_height="wrap_content" android:id="@+id/progress" style="?android:attr/progressBarStyleHorizontal" ></ProgressBar> <Button android:id="@+id/btnCancel" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Cancel" ></Button> </LinearLayout></pre><div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/February/Threading2/asynctask.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/February/Threading2/asynctask.png" width="224" /></a></div></div>Here we have two buttons: one to start progress and the other to stop it. Creating the AsyncTask sub class:</div>The first step in implementing AsyncTask is to create a sub class like this: <pre class="brush:java">class ProgressTask extends AsyncTask<Params, Progress, Result>{ }</pre>The AsyncTask declaration has three <a href="http://download.oracle.com/javase/1,5.0/docs/guide/language/varargs.html">Varargs</a> parameters which are: <ol><li>Params: parameter info passed to be used by the AsyncTask.</li><li>Progress: the type of progress that the task accomplishes.</li><li>The result returned after the AsyncTask finishes.</li></ol>These parameters are of type Varargs which provide the flexibility to pass dynamic sized arrays as parameters. In our example our class will be like this:</div><pre class="brush:java">class ProgressTask extends AsyncTask<Integer, Integer, Void>{ }</pre> The parameter and the progress are of type Integer and the result is Void as our tasks does not return anthing (returns null). The second step is overriding the protected methods defined by the AsyncTask class that handle the execution life cycle of the AsyncTask. We have five methods to implement which are: <ol><li>onPreExecute: the first method called in the AsyncTask, called on the UI thread.</li><li>doInBackground: the method that executes the time consuming tasks and publish the task progress, executed in background thread.</li><li>onProgressUpdate: method that updates the progress of the AsyncTask, run on the UI thread.</li><li>onPostExecute: the final method that gets called after doInBackground finishes, here we can update the UI with the results of the AsyncTask.</li><li>onCancelled: gets called if the AsyncTask.cancel() methods is called, terminating the execution of the AsyncTask.</li></ol> </div>Starting the AsyncTask:</div>To start the AsyncTask we create an instance of it, then call the execute() method passing the initial parameters like this: <pre>ProgressTask task=new ProgressTask(); // start progress bar with initial progress 10 task.execute(10);</pre>Implementing the AsyncTask: <pre class="brush:java">class ProgressTask extends AsyncTask<Integer, Integer, Void>{ @Override protected void onPreExecute() { // initialize the progress bar // set maximum progress to 100. progress.setMax(100); } @Override protected void onCancelled() { // stop the progress progress.setMax(0); } @Override protected Void doInBackground(Integer... params) { // get the initial starting value int start=params[0]; // increment the progress for(int i=start;i<=100;i+=5){ try { boolean cancelled=isCancelled(); //if async task is not cancelled, update the progress if(!cancelled){ publishProgress(i); SystemClock.sleep(1000); } } catch (Exception e) { Log.e("Error", e.toString()); } } return null; } @Override protected void onProgressUpdate(Integer... values) { // increment progress bar by progress value progress.setProgress(values[0]); } @Override protected void onPostExecute(Void result) { // async task finished Log.v("Progress", "Finished"); } }</pre> Here are the steps: <ol><li>onPreExecute() method first gets called initializing the maximum value of the progress bar.</li><li>doInBackground(Integer... params) methods gets called by obtaining the initial start value of the progress bar then incrementing the value of the progress bar every second and publishing the progress as long as the async task is not cancelled.</li><li>onProgressUpdate(Integer... values) method is called each time progress is published from doInBackground, thus incrementing the progress bar.</li><li>onPostExecute(Void result) is called after doInBackground finished execution.</li><li>void onCancelled() is called if task.cancel(true) is called from the UI thread. it may interrupt the execution preventing onPostExecute from being executed.</li></ol> </div>The onClick handler of our buttons is like this: <pre class="brush:java">@Override public void onClick(View v) { ProgressTask task=new ProgressTask(); switch(v.getId()){ case R.id.btn: task.execute(10); break; case R.id.btnCancel: task.cancel(true); break; } }</pre><div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/February/Threading2/asynctask2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/February/Threading2/asynctask2.png" width="222" /></a></div> </div>

In the previous post we saw one way to deal with threads in Android, which is by using Handlers . In this post we'll see how to use ano...

Threading in Android part 1: Handlers

<div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on"><div dir="ltr" style="text-align: left;" trbidi="on">Multi-Threading concept is essential in most platforms. it provides maximum utilization of the processor. threading is used when the program executes time consuming processes (such as calling a web service) and to give a good user experience by unblocking the UI. Android provides threading techniques to perform time consuming tasks in a background thread with coordination with the UI thread to update the UI. Android provides the following methods of threading: <ol style="text-align: left;"><li>Handlers.</li><li>Async. Tasks.</li></ol>Handlers:</div>When you create an object from the Handler class, it processes Messages and Runnable objects associated with the current thread MessageQueue. the message queue holds the tasks to be executed in FIFO (First In First Out) mannser. you will need only ine Handler per activity where the background thread will communicate with to update the UI. The Handler is associated with the thread from which it's been created We can communicate with the Handler by two methods: <ol><li>Messages.</li><li>Runnable objects.</li></ol>In this post we will demonstrate how to use both using a simple example which is updating the text of a TextView using multiple threads. Using Messages: the steps of using a Handler are as follows: <ol><li>You create a Handler object with an asscociated callback method to handle the received messages (it is the method where the UI update will be done).</li><li>From the background thread you will need to send messages to the handler.</li></ol>Here's the code of our activity:</div><pre class="brush:java">public class MainActivity extends Activity { TextView txt; // our handler Handler handler = new Handler() { @Override public void handleMessage(Message msg) {</pre><pre class="brush:java">//display each item in a single line txt.setText(txt.getText()+"Item "+System.getProperty("line.separator")); } }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); txt=(TextView)findViewById(R.id.txt); } @Override protected void onStart() { super.onStart(); // create a new thread Thread background=new Thread(new Runnable() { @Override public void run() { for(int i=0;i<10;i++) { try { Thread.sleep(1000); b.putString("My Key", "My Value: "+String.valueOf(i)); // send message to the handler with the current message handler handler.sendMessage(handler.obtainMessage()); } catch (Exception e) { Log.v("Error", e.toString()); } } } }); background.start(); } } </pre></div>after running the following code the TextView will display the following, each second a new line is written: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/February/Threading1/Threading.png" imageanchor="1" style="left: 1em; margin-right: 1em;"><img border="0" h5="true" height="320" src="http://dl.dropbox.com/u/2624328/Android %20Pro/2011/February/Threading1/Threading.png" width="227" /></a></div></div> This example is pretty basic, it just sends the same message for a number of times. what if we want the message sent to hold data that's changed each time the message is sent, the answer is to use Message.setData(Bundle bundle) method by creating a Bundle object and adding the data to it like this: <pre class="brush:java">public class MainActivity extends Activity { TextView txt; // our handler Handler handler = new Handler() { @Override public void handleMessage(Message msg) { // get the bundle and extract data by key Bundle b = msg.getData(); String key = b.getString("My Key"); txt.setText(txt.getText() + "Item " + key +System.getProperty("line.separator")); } }; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); txt = (TextView) findViewById(R.id.txt); } @Override protected void onStart() { super.onStart(); // create a new thread Thread background = new Thread(new Runnable() { @Override public void run() { for (int i = 0; i < 10; i++) { try { Thread.sleep(1000); Message msg = new Message(); Bundle b = new Bundle(); b.putString("My Key", "My Value: " + String.valueOf(i)); msg.setData(b); // send message to the handler with the current message handler handler.sendMessage(msg); } catch (Exception e) { Log.v("Error", e.toString()); } } } }); background.start(); } } </pre>we put a string to the bundle and send a message with that bundle. in the handler method we receive the bundle and get the value with the predefined key. after executing that code the text view would look like this: <div class="separator" style="clear: both; text-align: center;"><a href="http://dl.dropbox.com/u/2624328/Android%20Pro/2011/February/Threading1/Threading2.png" imageanchor="1" style="left: 1em; margin-right: 1em;"><img border="0" h5="true" height="320" src="http://dl.dropbox.com/u/2624328/Android %20Pro/2011/February/Threading1/Threading2.png" width="226" /></a></div></div> Using Runnables: another way to use Handlers is to pass them a Runnable by using the Handler.post() method like this:</div><pre class="brush:java">Runnable r=new Runnable() { @Override public void run() { txt.setText("Runnable"); } }; handler.post(r); </pre></div> this will add the Runanble object to the message queue to be executed by the handler. Sending Messages in a timely manner:</div>we can use handlers to send messages or post runnables at time intervals using the following methods: <ol><li>handler.sendEmptyMessageAtTime(int what,long uptimeMillis):sends an  empty message at a specific time in milli-seconds, can be defined by using the SystemClock.uptimeMillis() method to get the time since the device boot  in milli-seconds and concatinating to it.</li><li>handler.sendEmptyMessageDelayed(int what,long delayMillis):sends an  empty message after a certain amount of time in milli-seconds.</li><li>handler.sendMessageAtTime(Message msg,long uptimeMillis).</li><li>handler.sendMessageDelayed(Message msg,long delayMillis).</li><li>handler.postAtTime(Runnable r,long uptimeMillis).</li><li>handler.postAtTime(Runnable r,Object token,long uptimeMillis):posts a  runnable with an object as a distinguishing token.</li><li>handler.postDelayed(Runnable r,long delayMillis).</li></ol>All the above messages return a boolean indicating whether the message or the runnable has been placed successfully in the message queue. Removing Call backs:</div>if you want to remove a runnable or a message from the message queue, you can use the following methods: <ol style="text-align: left;"><li>handler.removeCallbacks(Runnable r).</li><li>handler.removeCallbacks(Runnable r,Object token).</li><li>handler.removeCallbacksAndMessages(Object token).</li><li>handler.removeMessages(int what).</li><li>handler.removeMessages(int what,Object object)</li></ol></div>

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<div dir="ltr" style="text-align: left;" trbidi="on">During updating your Android SDK components from eclipse (running in windows) you may receive the following error message: a folder failed to be renamed or moved... the message suggests that you turn of your anti-virus. I did so but still recieved the error. I terminated the adb.exe from the processes but still not solved. the problem is that the update batch is rin from android.bat file inside tools directory. update requires that this folder is renamed temporarily but since Windows 7 locks it the process halts with this error. so a workaround for this is to copy the tools folder, paste it in te sdk directory, name it tools_temp for example and run android.bat from this directory. the update shall go smooth, after finishing delete this temp folder and launch eclipse and it will work fine. note: after restarting eclipse you may recieve this error This Android SDK requires Android Developer Toolkit version 10.xxxxxxxxxx the current version is 9.xxxxxxxxxxxxxx. this is because the ADT plugin needs to be update after updating software components, go to <a href="http://developer.android.com/sdk/eclipse-adt.html">http://developer.android.com/sdk/eclipse-adt.html</a> and follow the instructions and everything will work after this.</div>

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Building Android Content Providers

Content providers are the way that Android applications can share info between each other. an application can ask for info from another application using content providers. In this post we're going to create a content provider to access data from our previous Employees simple application from the <a href="http://android-pro.blogspot.com/2010/10/using-sqlite-database-with-android.html">SQLite post</a>. to remind you the database has two tables Employees and Dept <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" height="133" ox="true" src="http://dl.dropbox.com/u/2624328/Android%20Pro/2010/October/SQLite%20DB/sqlitedb1.jpg" width="320" /></a></div>remember that any content provider must provide the following: <ol><li>A URi from which we can run queries.</li><li>MIME type corresponding to the content.</li><li>Insert() method.</li><li>Update() methd.</li><li>Delete() method.</li></ol> Creating the content type: first we will create a new class, I will call it EmployeesContentProvider and choose its super class to be ContentProvider. the class initially will be like this: <pre class="brush:java">package mina.android.DatabaseDemo; import android.content.ContentProvider; import android.content.ContentValues; import android.database.Cursor; import android.net.Uri; public class EmployeesContentProvider extends ContentProvider { DatabaseHelper db; public static final Uri CONTENT_URI=Uri.parse("content://employees"); @Override public int delete(Uri arg0, String arg1, String[] arg2) { // TODO Auto-generated method stub return 0; } @Override public String getType(Uri uri) { // TODO Auto-generated method stub return null; } @Override public Uri insert(Uri uri, ContentValues values) { // TODO Auto-generated method stub return null; } @Override public boolean onCreate() { // TODO Auto-generated method stub return false; } @Override public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { // TODO Auto-generated method stub return null; } @Override public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { // TODO Auto-generated method stub return 0; } } </pre> we added a member of type DatabaseHelper db to hold a reference to our database. also we added a static URi object that represents the URi of our content provider. it has all the abstract methods implementations of the ContentProvider class. so let's check each method onCreate() method: the onCreate() method is the first method invoked when the content provider is created (similar to the Activity's onCreate() method). here you can load your database or check for files you may read/write to them. the method return a Boolean. it should be true if everything is ok, otherwise it should be false. in our case we will just reference our SQLite database: <pre class="brush:java">@Override public boolean onCreate() { // TODO Auto-generated method stub db=new DatabaseHelper(this.getContext()); if(db==null) return false; else return true; } </pre> query() method: the query() method is the method that gets invoked when a content provider data is requested by a URi. but first let's talk a little about content providers URI. the content provider URi has the following format: <div style="text-align: center;">content://Authority/[(n) path]/[instance indentifier]</div>explanation: <ul><li>the URI starts with content:// scheme.</li><li>the authority is a unique identifier for the content provider.</li><li>the authority can be followed by one or more paths (optional) refer to data paths within the content.</li><li>there can be an instance identifier that refers to a specific data instance.</li></ul>for example we can have a URi like this content://Employees/Marketing//11. this URi has Employees as the authority, Marketing as a data path and 11 as an instance (employee) identifier. back to our query method, we have the following parameters: <ol><li>Uri: the URi requested.</li><li>String [] projection: representing the columns (projection) to be retrieved.</li><li>String[] selection: the columns to be included in the WHERE clause.</li><li>String[] selectionArgs: the values of the selection columns.</li><li>String sortOrder: the ORDER BY statement.</li></ol>the first step in our query method is to parse the client URi. we expect the URi to be in one of the following forms: <ol><li>content://employees/: retrieves all employees.</li><li>content://employees/id: retrieves a certain employee by ID.</li><li>content://employess/IT: retreives employees of IT Dept.</li><li>content://employess/HR: retrieves employees of HR Dept.</li><li>content://employees/Sales: retreives employees of sales Dept.</li></ol>so we will add some constatnt values to our class to refer to the above URis: <pre class="brush:java">//authority and paths public static final String AUTHORITY="employees"; public static final String ITPATH="IT"; public static final String HRPATH="HR"; public static final String SALESPATH="Sales"; //URiMatcher to match client URis public static final int ALLEMPLOYEES=1; public static final int SINGLEEMPLOYEE=2; public static final int IT=3; public static final int HR=4; public static final int SALES=5; </pre>then we're going to define a URiMatcher object that matches the client URi <pre class="brush:java">static final UriMatcher matcher=new UriMatcher(UriMatcher.NO_MATCH); static{ matcher.addURI(AUTHORITY,null,ALLEMPLOYEES); matcher.addURI(AUTHORITY, ITPATH, IT); matcher.addURI(AUTHORITY, HRPATH, HR); matcher.addURI(AUTHORITY, SALESPATH, SALES); //you can use '*' as a wild card for any text matcher.addURI(AUTHORITY, "#", SINGLEEMPLOYEE); } </pre>the static initializer block loads the URimatcher objects with the values to match when the class initializes. so let's write our query method: <pre class="brush:java">@Override public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) { SQLiteQueryBuilder builder=new SQLiteQueryBuilder(); builder.setTables(DatabaseHelper.viewEmps); String order=null; Cursor result=null; if(sortOrder!=null) order=sortOrder; int match=matcher.match(uri); switch(match) { case ALLEMPLOYEES: //content://employees//id result=builder.query(db.getWritableDatabase(), projection, selection, selectionArgs, null, null, sortOrder); break; case SINGLEEMPLOYEE: //content://employees//id List<string>segments=uri.getPathSegments(); String empID=segments.get(0); result=db.getEmpByID(empID); break; case IT: //content://employees//IT result=db.getEmpByDept("IT"); result=builder.query(db.getReadableDatabase(), projection, db.colDeptName+"=?", new String[]{"IT"}, null, null, sortOrder); break; case HR: //content://employees//HR result=db.getEmpByDept("HR"); result=builder.query(db.getReadableDatabase(), projection, db.colDeptName+"=?", new String[]{"HR"}, null, null, sortOrder); break; case SALES: //content://employees//Sales result=db.getEmpByDept("Sales"); result=builder.query(db.getReadableDatabase(), projection, db.colDeptName+"=?", new String[]{"Sales"}, null, null, sortOrder); break; } return result; } </pre> the function just parses the URi and returns the data in a cursor. Insert() method: the insert methods inserts a new record to the db; the insert method has the following form: <pre class="brush:java">public Uri insert(Uri uri, ContentValues values) { return null; } </pre>the method has two parameters: <ol><li>URi uri: the URi of the content provider, we need to check it's correct.</li><li>ContentValues values: object holding the info of the new item to be inserted.</li></ol>the method returns the URi of the newly inserted item to be used for further manipulations. so here's the implentation: <pre class="brush:java">@Override public Uri insert(Uri uri, ContentValues values) { int match=matcher.match(uri); //not the Uri we're expecting long newID=0; if(match!=1) throw new IllegalArgumentException("Wrong URi "+uri.toString()); if(values!=null) { newID=db.getWritableDatabase().insert(DatabaseHelper.employeeTable, DatabaseHelper.colName, values); return Uri.withAppendedPath(uri, String.valueOf(newID)); } else return null; } </pre>we first check the Uri if it is not correct, throw an exception. then check the content values object, if null return null otherwise insert the new item and return the URi with the id of the new item. the Update() method: the update method updates existing record(s) and returns the number of updated rows. a trick rises from the fact that you need to specify whether to update a collection of records or a single record, based on the URi. the method has the following parameters: <ol><li>URi uri: the URi of the content provider, we need to check it's correct.</li><li>ContentValues values: object holding the info of the new item to be inserted.</li><li>String Selection : the filter to match the rows to update</li><li>String [] selectionArgs : the values of the filter parameters</li></ol>here's the implementation of the update method: <pre class="brush:java">@Override public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) { int match=matcher.match(uri); //not the Uri we're expecting int rows=0; //update single instance if(match==2) { if(values!=null) { List<string>segments=uri.getPathSegments(); String empID=segments.get(0); rows=db.getWritableDatabase().update(DatabaseHelper.employeeTable, values,DatabaseHelper.colID+"=?", new String []{empID}); } } //update all emps in a certain dept else if(match==3 ||match==4||match==5) { List<string>segments=uri.getPathSegments(); String deptName=segments.get(0); int DeptID=db.GetDeptID(deptName); rows=db.getWritableDatabase().update(db.employeeTable, values,db.colDept+"=?", new String []{String.valueOf(DeptID)}); } return rows; } </pre>the Delete() method: the delete method has the following parameters: <ol><li>Uri uri: the URi of the content provider.</li><li>String Condition: the condition of the delete statement.</li><li>String[] args: the delete condition arguments</li></ol> so here's the implementation: <pre class="brush:java">@Override public int delete(Uri uri, String where, String[] args) { int match=matcher.match(uri); //expecting the URi to be in the form of if(match==1) { SQLiteDatabase dataBase=db.getWritableDatabase(); return dataBase.delete(db.employeeTable, where, args); } else return 0; } </pre>we just check for the URi and perform a delete command. The getType() method: the last mthod to implement is getType() method which returns the MIME type associated with the URi passed to it. if the URi is of a group of employees, then the MIME type is a collection type, otherwise it's of an instance type <pre class="brush:java">@Override public String getType(Uri uri) { int match=matcher.match(uri); // single employee if(match==2) { return "mina.android.Employee"; } //collection of employees else { return "mina.android.Employees"; } } </pre>Modifying the Manifest.xml file: the last thing we need to do is to add an entry in our application's manifest.xml file to register our class as a content provider class. so add this entry just below the <application> <pre class="brush:xml"><provider android:name="mina.android.DatabaseDemo.EmployeesContentProvider" android:authorities="employees"/> </pre>the when an application requests data through our content provider, Android system will search all the manifest files of all aplications on the device and when it finds such an entry, it will process the request Testing the content provider: now suppose you are in another activity and you want to use our activity. Testing queries: to make a query to retrieve all employees: <pre class="brush:java">Uri empsUri=Uri.parse("content://employees"); Cursor cursor=getContentResolver().query(empsUri, null, null, null, null);Cursor cursor=getContentResolver().query(empsUri, null, null, null, null); </pre>the cursor should have all the records. to retrieve a certain employee by ID or all employees in a certain department: <pre class="brush:java">Uri empUri=Uri.parse("content://employees//5"); Uri empDeptUri=Uri.parse("content://employees//Sales"); </pre> Inserting: <pre class="brush:java">Uri empsUri=Uri.parse("content://employees"); ContentValues cvs=new ContentValues(); cvs.put("EmployeeName", "Mark Anderson"); cvs.put("Age", 35); cvs.put("Dept", 1); // URi of the new inserted item Uri newEmp=getContentResolver().insert(empsUri, cvs); </pre> Updating: to update a single employee: <pre class="brush:java">//Uri with the id of the employee Uri empsUri=Uri.parse("content://employees/8"); Cursor cursor=getContentResolver().query(empsUri, null, null, null, null); txt.setText(String.valueOf(cursor.getCount())); ContentValues cvs=new ContentValues(); cvs.put("EmployeeName", "Mina Samy mod"); cvs.put("Age", 35); cvs.put("Dept", 1); // number of rows modified int rowsNumber=getContentResolver().update(empsUri, cvs, "EmployeeID=?", new String[]{"8"}); </pre>to update all employees in a certain department <pre class="brush:java">Uri empsUri=Uri.parse("content://employees/Sales"); Cursor cursor=getContentResolver().query(empsUri, null, null, null, null); txt.setText(String.valueOf(cursor.getCount())); ContentValues cvs=new ContentValues(); cvs.put("EmployeeName", "mod"); cvs.put("Age", 35); cvs.put("Dept", 1); int rowsNumber=getContentResolver().update(empsUri, cvs, "colDept=?", new String[]{"1"}); </pre> as a matter of fact, in both cases we don't need to specify the wher clause and the where parameters as they are implicitly specified in the URi. so we just can replace the update statement to be like this: <pre class="brush:java">int rowsNumber=getContentResolver().update(empsUri, cvs, null,null); </pre> Deleting: I left the delete operation open to any criteria, you can delete a single employee or employees of a certain department or even all employees <pre class="brush:java">Uri empsUri=Uri.parse("content://employees"); // delete employee of id 8 int rowsNumber=getContentResolver().delete(empsUri,"EmployeeID=?",new String[]{"8"}); </pre> Final Word: creating a content provider for a certain type of data can be done in many ways, this example can be implemented in several variations. another thing is that you need to create a strongly typed class for you data model to be used by clients accessing your content. in this example when I tested the query i wrote the column names of the database as strings like this: "EmployeeID" and "EmployeeName". this is not ideal in a production release of an application. I should created a class library that holds all the info about the database to be used by other client applications. you can download the source code for this example from <a href="http://uploading.com/files/f5ac154b/Database%2BDemo%2B%2B%2BContent%2Bprovider.rar/">here</a>.

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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...