Question

I am developing simple application with only two activities.

• Activity C configures application
• Activity A for interaction with user when some event occur

It is not possible for user to navigate from the one to the other – this is why I call them independent activities. Further more activity A is being invoked only form event, there is no way for user to do it manually.

Problem. Let’s assume that application is properly configured. Some event occurs in the system, so application A is being shown to the user. The user interact with it and activity goes to background. Then the user decides to launch configuration activity C. Activity C is shown to the user. The user uses back button to “close” activity, but instead of android launcher or desktop the user is being shown activity A (taken from history).

Similar scenario might happen the other way. C is being used by user, then taken to background. Some event shows activity A and user using back button goes to C instead of closing activity A.

I have solved the problem, but the solution is pretty dirty. Is there any clean or standard way of solving such problem?

Part of my solution includes what was suggested in one answer:

snippet from AndroidManifest.xml:

<activity
  android:name=".C"
  android:clearTaskOnLaunch="true"
  android:excludeFromRecents="false"
  android:launchMode="singleTask"
  ...
 >
  <intent-filter>
    <action android:name="android.intent.action.MAIN" />
    <category android:name="android.intent.category.LAUNCHER" />
  </intent-filter>
</activity>
<activity
  android:exported="false"
  android:name=".A"
  android:excludeFromRecents="true"
  android:noHistory="true"
  android:launchMode="singleInstance"
  android:clearTaskOnLaunch="true"
  ....
>
</activity>

snippet from activity A:

public boolean onKeyUp(final int p_keyCode, final KeyEvent p_event) {
    switch(p_keyCode) {
        case KeyEvent.KEYCODE_ENDCALL:
        case KeyEvent.KEYCODE_HOME:
        case KeyEvent.KEYCODE_BACK:
        case KeyEvent.KEYCODE_MUTE:
        case KeyEvent.KEYCODE_POWER:
            this.finish();
            break;
        ....
    }
    return super.onKeyUp(p_keyCode, p_event);
}

snipped from event handler:

public class H extends BroadcastReceiver {
...
  Intent intent = new Intent(p_context, A.class);
  intent.addFlags(Intent.FLAG_FROM_BACKGROUND);
  intent.addFlags(Intent.FLAG_ACTIVITY_NO_USER_ACTION);
  intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
  p_context.startActivity(intent);
...
}

It works for my application. However I want application (activity C) to appear in Recent application. But once activity A is invoked application is removed from Recent.

Answer 1

I don’t know if this is the cleanest way to do this, but you can override the void onBackPressed() activity method. This way you can mannually move your activity to the background, like this, and prevent the previous activity from popping in:

public void onBackPressed () {
    moveTaskToBack (true);
}

Edit: Turns out there’s a better way to do this:

Open your AndroidManifest.xml, and inside each declaration put the following: `android:noHistory=”true”“. Doing so will tell Android that your activity does not leave a history, and therefore, when the user hits back Android will quit the application, since there’s no other activity for it to return to.