如何在我的android应用程序中显示应用程序覆盖屏幕？

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

<Button
    android:id="@+id/float_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="悬浮按钮" />

public class FloatWindowService extends Service {

    private WindowManager windowManager;
    private WindowManager.LayoutParams layoutParams;
    private View floatView;

    @Override
    public void onCreate() {
        super.onCreate();
        windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
        layoutParams = new WindowManager.LayoutParams();
        layoutParams.type = WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY;
        layoutParams.format = PixelFormat.RGBA_8888;
        layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
        layoutParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
        layoutParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
        layoutParams.gravity = Gravity.TOP | Gravity.LEFT;
        layoutParams.x = 0;
        layoutParams.y = 0;
        floatView = LayoutInflater.from(this).inflate(R.layout.float_window, null);
        windowManager.addView(floatView, layoutParams);
    }

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

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

Intent intent = new Intent(this, FloatWindowService.class);
startService(intent);