Overlay button over device

gistfile1.txt

import android.app.Service;
import android.content.Intent;
import android.graphics.PixelFormat;
import android.os.IBinder;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.View;
import android.view.WindowManager;
import android.widget.ImageView;

public class FloatingButtonService extends Service {

	private WindowManager windowManager;
	private ImageView appButton;
	WindowManager.LayoutParams params;

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

		windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);

		appButton = new ImageView(this);
		appButton.setImageResource(R.drawable.ic_play_arrow_white);

		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;

		//this code is for dragging the chat head
		appButton.setOnTouchListener(new View.OnTouchListener() {
			private int initialX;
			private int initialY;
			private float initialTouchX;
			private float initialTouchY;

			@Override
			public boolean onTouch(View v, MotionEvent event) {
				switch (event.getAction()) {
				case MotionEvent.ACTION_DOWN:
					initialX = params.x;
					initialY = params.y;
					initialTouchX = event.getRawX();
					initialTouchY = event.getRawY();
					return true;
				case MotionEvent.ACTION_UP:
					return true;
				case MotionEvent.ACTION_MOVE:
					params.x = initialX
							+ (int) (event.getRawX() - initialTouchX);
					params.y = initialY
							+ (int) (event.getRawY() - initialTouchY);
					windowManager.updateViewLayout(appButton, params);
					return true;
				}
				return false;
			}
		});
		windowManager.addView(appButton, params);
	}

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

	@Override
	public IBinder onBind(Intent intent) {
		// TODO Auto-generated method stub
		return null;
	}
}

<--------------------->

    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW"/>
    
    <service
            android:name=".FloatingButtonService"
            android:enabled="true"
            android:exported="true"/>

Works great, for TargetSDK>=23 use : if (!Settings.canDrawOverlays(this)) startActivity( Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION)) to ask for SYSTEM_ALERT_WINDOW permission