android app在后台运行弹出弹窗

public class PopupService extends Service {
    private WindowManager windowManager;
    private View popupView;
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
    @Override
    public void onCreate() {
        super.onCreate();
        windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
        // 在这里创建弹窗的视图
        popupView = LayoutInflater.from(this).inflate(R.layout.popup_view, null);
        // 设置弹窗的位置等属性
        WindowManager.LayoutParams params = new WindowManager.LayoutParams(
                WindowManager.LayoutParams.WRAP_CONTENT,
                WindowManager.LayoutParams.WRAP_CONTENT,
                WindowManager.LayoutParams.TYPE_APPLICATION_OVERLAY, // 支持在其他App上方显示
                WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE,
                PixelFormat.TRANSPARENT);
        params.gravity = Gravity.CENTER;
        windowManager.addView(popupView, params);
    }
    @Override
    public void onDestroy() {
        super.onDestroy();
        if (popupView != null && windowManager != null) {
            windowManager.removeView(popupView);
        }
    }
}

public class MainActivity extends AppCompatActivity {
    private Intent popupServiceIntent;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        popupServiceIntent = new Intent(this, PopupService.class);
    }
    @Override
    protected void onResume() {
        super.onResume();
        stopService(popupServiceIntent);
    }
    @Override
    protected void onPause() {
        super.onPause();
        startService(popupServiceIntent);
    }
}

<LinearLayout xmlns:android="
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:background="#FFFFFF"
    android:padding="16dp">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="这是一个