홈 버튼 오버라이드

public class MyApplication extends Application {
    // ...
    @Override
       public void onCreate() {
           super.onCreate();
 
           registerActivityLifecycleCallbacks(new Application.ActivityLifecycleCallbacks() {
               // ...
               @Override
               public void onActivityResumed(Activity activity) {
                 if (isBackground) {
                     isBackground = false;
                     notifyForeground();
                 }
               }
               // ...
           });
       }
       // ...
}
Tying It All Together
Alright, here is a more complete sample to be notified when the app enters foreground and is sent to background.
 
public class MyApplication extends Application {
 
    // Starts as true in order to be notified on first launch
    private boolean isBackground = true;
 
    @Override
    public void onCreate() {
        super.onCreate();
 
        listenForForeground();
        listenForScreenTurningOff();
    }
 
    private void listenForForeground() {
        registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
            //...
            @Override
            public void onActivityResumed(Activity activity) {
                if (isBackground) {
                    isBackground = false;
                    notifyForeground();
                }
            }
            //...
        });
    }
 
    private void listenForScreenTurningOff() {
        IntentFilter screenStateFilter = new IntentFilter(Intent.ACTION_SCREEN_OFF);
        registerReceiver(new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                isBackground = true;
                notifyBackground();
            }
        }, screenStateFilter);
    }
 
    @Override
    public void onTrimMemory(int level) {
        super.onTrimMemory(level);
        if (level == TRIM_MEMORY_UI_HIDDEN) {
            isBackground = true;
            notifyBackground();
        }
 
    }
 
    private void notifyForeground() {
        // This is where you can notify listeners, handle session tracking, etc
    }
 
    private void notifyBackground() {
        // This is where you can notify listeners, handle session tracking, etc
    }
 
    public boolean isBackground() {
      return isBackground;
    }
}