What APIs are used to draw over other apps (like Facebook's Chat Heads)?

Question

How does Facebook create the Chat Heads on Android? What is the API to create the floating views on top of all other views?

Answer 1

This one:

Allows an application to open windows using the type TYPE_SYSTEM_ALERT, shown on top of all other applications. Very few applications should use this permission; these windows are intended for system-level interaction with the user.

Constant Value: "android.permission.SYSTEM_ALERT_WINDOW"

//EDIT: The full code here:

public class ChatHeadService extends Service {

  private WindowManager windowManager;
  private ImageView chatHead;

  @Override public IBinder onBind(Intent intent) {
    // Not used
    return null;
  }

  @Override public void onCreate() {
    super.onCreate();

    windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);

    chatHead = new ImageView(this);
    chatHead.setImageResource(R.drawable.android_head);

    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);

    params.gravity = Gravity.TOP | Gravity.LEFT;
    params.x = 0;
    params.y = 100;

    windowManager.addView(chatHead, params);
  }

  @Override
  public void onDestroy() {
    super.onDestroy();
    if (chatHead != null) windowManager.removeView(chatHead);
  }
}

Don't forget to start the service somehow:

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

.. And add this service to your Manifest.