Creating a System Overlay (Always on Top over all Apps) in Android

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="de.mobilej.overlay"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="14" />

    <application android:label="SystemOverlay" >
        <activity
            android:name="de.mobilej.overlay.Main"
            android:exported="true" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <service
            android:name="de.mobilej.overlay.OverlayShowingService"
            android:exported="false" />
    </application>

    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

</manifest>

Main.java

package de.mobilej.overlay;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;

public class Main extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Intent svc = new Intent(this, OverlayShowingService.class);
        startService(svc);
        finish();
    }
}

OverlayShowingService.java

package de.mobilej.overlay;

import android.app.Service;
import android.content.Context;
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.View.OnClickListener;
import android.view.View.OnTouchListener;
import android.view.WindowManager;
import android.view.WindowManager.LayoutParams;
import android.widget.Button;
import android.widget.Toast;

public class OverlayShowingService extends Service implements OnTouchListener, OnClickListener {
    
    private View topLeftView;

    private Button overlayedButton;
    private float offsetX;
    private float offsetY;
    private int originalXPos;
    private int originalYPos;
    private boolean moving;
    private WindowManager wm;

    @Override
    public IBinder onBind(Intent intent) {
	return null;
    }

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

	wm = (WindowManager) getSystemService(Context.WINDOW_SERVICE);

	overlayedButton = new Button(this);
	overlayedButton.setText("Overlay button");
	overlayedButton.setOnTouchListener(this);
	overlayedButton.setAlpha(0.0f);
	overlayedButton.setBackgroundColor(0x55fe4444);
	overlayedButton.setOnClickListener(this);

	WindowManager.LayoutParams params = new WindowManager.LayoutParams(WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.TYPE_SYSTEM_ALERT, WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL, PixelFormat.TRANSLUCENT);
	params.gravity = Gravity.LEFT | Gravity.TOP;
	params.x = 0;
	params.y = 0;
	wm.addView(overlayedButton, params);

	topLeftView = new View(this);
	WindowManager.LayoutParams topLeftParams = new WindowManager.LayoutParams(WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.WRAP_CONTENT, WindowManager.LayoutParams.TYPE_SYSTEM_ALERT, WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE | WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL, PixelFormat.TRANSLUCENT);
	topLeftParams.gravity = Gravity.LEFT | Gravity.TOP;
	topLeftParams.x = 0;
	topLeftParams.y = 0;
	topLeftParams.width = 0;
	topLeftParams.height = 0;
	wm.addView(topLeftView, topLeftParams);

    }

    @Override
    public void onDestroy() {
	super.onDestroy();
	if (overlayedButton != null) {
	    wm.removeView(overlayedButton);
	    wm.removeView(topLeftView);
	    overlayedButton = null;
	    topLeftView = null;
	}
    }

    @Override
    public boolean onTouch(View v, MotionEvent event) {

	if (event.getAction() == MotionEvent.ACTION_DOWN) {
	    float x = event.getRawX();
	    float y = event.getRawY();

	    moving = false;

	    int[] location = new int[2];
	    overlayedButton.getLocationOnScreen(location);

	    originalXPos = location[0];
	    originalYPos = location[1];

	    offsetX = originalXPos - x;
	    offsetY = originalYPos - y;

	} else if (event.getAction() == MotionEvent.ACTION_MOVE) {
	    int[] topLeftLocationOnScreen = new int[2];
	    topLeftView.getLocationOnScreen(topLeftLocationOnScreen);

	    System.out.println("topLeftY="+topLeftLocationOnScreen[1]);
	    System.out.println("originalY="+originalYPos);
	    
	    float x = event.getRawX();
	    float y = event.getRawY();

	    WindowManager.LayoutParams params = (LayoutParams) overlayedButton.getLayoutParams();

	    int newX = (int) (offsetX + x);
	    int newY = (int) (offsetY + y);

	    if (Math.abs(newX - originalXPos) < 1 && Math.abs(newY - originalYPos) < 1 && !moving) {
		return false;
	    }

	    params.x = newX - (topLeftLocationOnScreen[0]);
	    params.y = newY - (topLeftLocationOnScreen[1]);

	    wm.updateViewLayout(overlayedButton, params);
	    moving = true;
	} else if (event.getAction() == MotionEvent.ACTION_UP) {
	    if (moving) {
		return true;
	    }
	}

	return false;
    }

    @Override
    public void onClick(View v) {
	Toast.makeText(this, "Overlay button click event", Toast.LENGTH_SHORT).show();
    }

}