Article Archive For Month : September 2010

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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>

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>

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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 the user.another way to show interactive messages is to use Alerts. alerts act as MessageBox or JOptionPane in …

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Using Android SlidingDrawer

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