How to draw a view on top of everything?

Question

I want to make an app that can create notification on the screen on top of anything that is currently being displayed. Something like the Go SMS message popup or something l

Answer 1

Here is how things like Toast and dialog windows work:

In the case where just adding or bringing to front does not work, say when you are having a service add its own view to another client activity or application (FaceUnlock does this), or you cannot depend on hierarchies, you need to use the window manager and a window token to do the trick. You can then create layouts and take advantage of animations and hardware acceleration as before.

    WindowManager windowManager = (WindowManager) getBaseContext().getSystemService(Context.WINDOW_SERVICE);

    WindowManager.LayoutParams layoutParams = new WindowManager.LayoutParams(WindowManager.LayoutParams.FIRST_SUB_WINDOW);
    layoutParams.width = 300;
    layoutParams.height = 300;

    layoutParams.format = PixelFormat.RGBA_8888;
    layoutParams.flags =
            WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
                    | WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
    layoutParams.token = getWindow().getDecorView().getRootView().getWindowToken();

    //Feel free to inflate here
    mTestView = new View(this);
    mTestView.setBackgroundColor(Color.RED);

    //Must wire up back button, otherwise it's not sent to our activity
    mTestView.setOnKeyListener(new View.OnKeyListener() {
        @Override
        public boolean onKey(View v, int keyCode, KeyEvent event) {
            if (keyCode == KeyEvent.KEYCODE_BACK) {
                onBackPressed();
            }
            return true;
        }
    });
    windowManager.addView(mTestView, layoutParams);

Then be sure to remove the view onDestroy (or onPause) or you will crash

   if (mTestView != null) {
       WindowManager windowManager = (WindowManager) getBaseContext().getSystemService(Context.WINDOW_SERVICE);
       if (mTestView.isShown()) {
            windowManager.removeViewImmediate(mTestView);
       }
   }