Android - Showing Overlay Window on top of all activities

This can be achieved if we are using the SYSTEM_ALERT_WINDOW. As per the API document, this should be used by only very few Apps. 

these windows are intended for system-level interaction

Code looks something like this 

public class OverlayViewService extends Service

{

private WindowManager windowManager; 

private ImageView overlayViewImage;

@override public IBinder onBind(Intent intent)

{

return null;

}

@override public voice onCreate()

{

super.onCreate();

windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);

overlayViewImage = new ImageView(this);

overlayViewImage.setImageResource(R.drawable.overlay_image);

WindowManager.LayoutParams params = new WindowManager.LayoutParams(

WindowManager.LayoutParams.WRAP_CONTENT,

WindowManager.LayoutParams.WRAP_CONTENT,

WindowManager.LayoutParams.TYPE_PHONE,

WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,

PixelForamt.TRANSLUCENT

);

params.gravity = Gravity.TOP | Gravity.LEFT;

params.x = 0;

params.y = 100;

windowManager.addView(overlayViewImage, params);

}

@override

public void onDestroy()

{

super.onDestroy();

if(overlayViewImage != null) windowManager.removeView(overlayViewImage);

}

}

now start the service like below 

startService(new Intent(context, OverlayViewService.class));

References:

http://www.piwai.info/chatheads-basics/

http://developer.android.com/reference/android/Manifest.permission.html#SYSTEM_ALERT_WINDOW