How to implement a popup overlay that can be displayed over any other app in Android

Question

How can I implement a popup overlay for an app that can be displayed over any other app.

Facebook implemented a very similar feature called Chatheads in its new Fac

Answer 1

Every Activity, dialog as well as service is attached with a window. Facebook keeps a service running in background and in the service they fetch window manager object by

windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);

Create Layout Params needed while adding your view

WindowManager.LayoutParams params = new WindowManager.LayoutParams(
    WindowManager.LayoutParams.WRAP_CONTENT,
    WindowManager.LayoutParams.WRAP_CONTENT,
    WindowManager.LayoutParams.TYPE_PHONE,
    WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
    PixelFormat.TRANSLUCENT);

now add your view to window manager by following method

windowManager.addView(yourView, params);