Android : Android: Service stops by closing Activity

I created an overlay view from this tutorial : http://www.piwai.info/chatheads-basics/

This is my Service Class:

public class CustomService extends Service{

    private WindowManager mWindowsManger;
    private ImageView mFloatingImage;
    private WindowManager.LayoutParams mParams;



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

    @Override
    public void onCreate() {
        super.onCreate();
        mWindowsManger = (WindowManager) getSystemService(WINDOW_SERVICE);

        mFloatingImage= new ImageView(this);
        mFloatingImage.setImageResource(R.mipmap.ic_launcher);
        mFloatingImage.setAlpha(0.5f);
        mParams = new WindowManager.LayoutParams(
                WindowManager.LayoutParams.WRAP_CONTENT,
                WindowManager.LayoutParams.WRAP_CONTENT,
                WindowManager.LayoutParams.TYPE_PHONE,
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
                PixelFormat.TRANSLUCENT);

        mParams.gravity = Gravity.TOP | Gravity.LEFT;
        mParams.x = 0;
        mParams.y = 100;
        mWindowsManger.addView(mFloatingImage, mParams);

        mFloatingImage.setOnTouchListener(new CustomTouchListener(this));

    }


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

And this is my activity where CustomService starts

public class MainActivity extends ActionBarActivity {


    @Override
    protected void onStart() {
        super.onStart();
        startService(new Intent(this, CustomService.class););
    }
...
}

Now my problem is whenever i close activity ,my service stopped and disappeared or onCreate method of CustomService called and it's going to recreating it.

Any ideas?