Controlling the Orientation of the Activity

"Occasionally you might want to ensure that your application is only displayed in a certain orientation."

For example, you may be writing a game that should only be viewed in landscape mode. In this
case, you can programmatically force a change in orientation using the setRequestOrientation()
method of the Activity class:




import android.content.pm.ActivityInfo;
public class MainActivity extends Activity {
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main);
         setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
          }


To change to portrait mode, use the ActivityInfo.SCREEN_ORIENTATION_PORTRAIT constant:
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

Besides using the setRequestOrientation() method, you can also use the android:screenOrientation
attribute on the <activity> element in AndroidManifest.xml as follows to constrain the activity to a
certain orientation:
 <?xml version=”1.0” encoding=”utf-8”?>
       <manifest xmlns:android=”http://schemas.android.com/apk/res/android”
              package=”net.learn2develop.Orientations”
               android:versionCode=”1”
               android:versionName=”1.0”>
       <application android:icon=”@drawable/icon” android:label=”@string/app_name”>
        <activity android:name=”.MainActivity”
            android:label=”@string/app_name”
                   android:screenOrientation=”landscape” >
          <intent-filter>
      <action android:name=”android.intent.action.MAIN” />
     <category android:name=”android.intent.category.LAUNCHER” />
   </intent-filter>
</application>
<uses-sdk android:minSdkVersion=”9” />
</manifest>

Following are two other values that you can specify in the android:screenOrientation attribute:
       1.  portrait — Portrait mode
       2.  sensor — Based on the accelerometer

Displaying Notifications

So far, you have been using the Toast class to display messages to the user. While the Toast class is
a handy way to show users alerts, it is not persistent. It flashes on the screen for a few seconds and
then disappears. If it contains important information, users may easily miss it if they are not looking
at the screen.
For messages that are important, you should use a more persistent method. In this case, you should
use the Notification Manager to display a persistent message at the top of the device, commonly
known as the status bar (sometimes also referred to as the notification bar). The following Try It
Out demonstrates how.

STEPS

1. Using Eclipse, create a new Android project and name it Notifications.

2. Add a new class file named NotificationView.java to the src folder of the project (see Figure 2-26).
    In addition, add a new notification.xml file to the res/layout folder as well.
    Figure 2-26

3. Populate the notification.xml file as follows:
   <?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=”Here are the details for the notification...” />
  </LinearLayout>

4. Populate the NotificationView.java file as follows:
   package net.learn2develop.Notifications;
   import android.app.Activity;
   import android.app.NotificationManager;
   import android.os.Bundle;
   public class NotificationView extends Activity
  {
    @Override
     public void onCreate(Bundle savedInstanceState)
    {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.notification);
    //---look up the notification manager service---
    NotificationManager nm = (NotificationManager)
    getSystemService(NOTIFICATION_SERVICE);
   //---cancel the notification that we started
   nm.cancel(getIntent().getExtras().getInt(“notificationID”));
   }
}

5. Add the following statements in bold to the AndroidManifest.xml file:
   <?xml version=”1.0” encoding=”utf-8”?>
   <manifest xmlns:android=”http://schemas.android.com/apk/res/android”
   package=”net.learn2develop.Notifications”
   android:versionCode=”1”
   android:versionName=”1.0”>
  <application android:icon=”@drawable/icon” android:label=”@string/app_name”>
  <activity android:name=”.MainActivity”
  android:label=”@string/app_name”>
  <intent-filter>
  <action android:name=”android.intent.action.MAIN” />
  <category android:name=”android.intent.category.LAUNCHER” />
  </intent-filter>
  </activity>
  <activity android:name=”.NotificationView”
  android:label=”Details of notification”>
  <intent-filter>
  <action android:name=”android.intent.action.MAIN” />
  <category android:name=”android.intent.category.DEFAULT” />
  </intent-filter>
  </activity>
  </application>
  <uses-sdk android:minSdkVersion=”9” />
  <uses-permission android:name=”android.permission.VIBRATE” />
</manifest>

6. Add the following statements in bold to the main.xml file:
  <?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” >
  <Button
  android:id=”@+id/btn_displaynotif”
  android:layout_width=”fill_parent”
  android:layout_height=”wrap_content”
  android:text=”Display Notification” />
  </LinearLayout>

7. Finally, add the following statements in bold to the MainActivity.java file:
   package net.learn2develop.Notifications;
   import android.app.Activity;
   import android.os.Bundle;
  import android.app.Notification;
  import android.app.NotificationManager;
   import android.app.PendingIntent;
  import android.content.Intent;
  import android.view.View;
  import android.widget.Button;
  public class MainActivity extends Activity {
  int notificationID = 1;
   public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main);
  Button button = (Button) findViewById(R.id.btn_displaynotif);
  button.setOnClickListener(new Button.OnClickListener() {
  public void onClick(View v) {
  displayNotification();
}
});
}
protected void displayNotification()
{
  Intent i = new Intent(this, NotificationView.class);
  i.putExtra(“notificationID”, notificationID);
  PendingIntent pendingIntent =
  PendingIntent.getActivity(this, 0, i, 0);
 NotificationManager nm = (NotificationManager)
  getSystemService(NOTIFICATION_SERVICE);
 Notification notif = new Notification(
 R.drawable.icon,
“ Reminder: Meeting starts in 5 minutes”,
 System.currentTimeMillis());
 CharSequence from = “System Alarm”;
 CharSequence message = “Meeting with customer at 3pm...”;
 notif.setLatestEventInfo(this, from, message, pendingIntent);
  notif.vibrate = new long[] { 100, 250, 100, 500};
  nm.notify(notificationID, notif);
}
}

8. Press F11 to debug the application on the Android Emulator.

9. Click the Display Notification button (see the top left of Figure 2-27) and a notification will appear
on the status bar.

10. Clicking and dragging the status bar down will reveal the notification (see the right of Figure).

11. Clicking on the notification will reveal the NotificationView activity. This also causes the
notification to be dismissed from the status bar.



                                                               Displaying Notifications