Wake lock removed but screen still not turning off when app is active

Question

I had the WAKE_LOCK permission in my app which I subsequently removed. But the phone still does not turn off the screen when my app is active. Is there any other setting that I might have that's preventing the phone from turning off?

Answer 1

There are a couple 'settings' that can prevent the screen from going to sleep, according to the docs:

Certain apps need to keep the screen turned on, such as games or movie apps. The best way to do this is to use the FLAG_KEEP_SCREEN_ON in your activity (and only in an activity, never in a service or other app component). For example:

public class MainActivity extends Activity {
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
  }

The advantage of this approach is that unlike wake locks (discussed in Keep the CPU On), it doesn't require special permission, and the platform correctly manages the user moving between applications, without your app needing to worry about releasing unused resources.

Another way to implement this is in your application's layout XML file, by using the android:keepScreenOn attribute:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:keepScreenOn="true">
    ...
</RelativeLayout>

Using android:keepScreenOn="true" is equivalent to using FLAG_KEEP_SCREEN_ON. You can use whichever approach is best for your app. The advantage of setting the flag programmatically in your activity is that it gives you the option of programmatically clearing the flag later and thereby allowing the screen to turn off.

Note: You don't need to clear the FLAG_KEEP_SCREEN_ON flag unless you no longer want the screen to stay on in your running application (for example, if you want the screen to time out after a certain period of inactivity). The window manager takes care of ensuring that the right things happen when the app goes into the background or returns to the foreground. But if you want to explicitly clear the flag and thereby allow the screen to turn off again, use clearFlags():

getWindow().clearFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON).

Wakelock is another, but since you already know about that, I don't think I need to mention that here.