Java Display Manager的Flatter和Android之间的事件通道

我正在尝试创建一个事件频道，以监听显示管理器的更改，我检查了android的文档，它在本机android上运行良好，下面是代码

public class MainActivity extends AppCompatActivity implements DisplayManager.DisplayListener{
    private  TextView mirrorText;

    private DisplayManager mDisplayManager;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mirrorText =  findViewById(R.id.mirrorName);
        mirrorText.setText("Mirroring");



        mDisplayManager = (DisplayManager)getSystemService(Context.DISPLAY_SERVICE);
        mDisplayManager.registerDisplayListener(MainActivity.this, null);
        mDisplayManager.unregisterDisplayListener(MainActivity.this);


    }

    @Override
    public void onDisplayAdded(int displayId) {
        mirrorText.setText("An new Display added with ID " + displayId);
    }

    @Override
    public void onDisplayRemoved(int displayId) {
        mirrorText.setText("An Display has been removed with ID " + displayId);
    }

    @Override
    public void onDisplayChanged(int displayId) {
        mirrorText.setText("Display changed added with ID " + displayId);
    }
}

public class MainActivity extends FlutterActivity implements DisplayManager.DisplayListener{
    private static final String MIRROR_CHANNEL = "com.example.andro/mirror";
    private int numberOfDiplay = 0;
    private DisplayManager mDisplayManager;


    @Override
    public void configureFlutterEngine(@NonNull FlutterEngine flutterEngine) {
        mDisplayManager = (DisplayManager)getSystemService(Context.DISPLAY_SERVICE);
        GeneratedPluginRegistrant.registerWith(flutterEngine);

        new EventChannel(flutterEngine.getDartExecutor(), MIRROR_CHANNEL).setStreamHandler(
                new StreamHandler() {
                    private BroadcastReceiver mirrorStateChangeReceiver;
                    @Override
                    public void onListen(Object arguments, EventSink events) {
                        mDisplayManager.registerDisplayListener(MainActivity.this, null);
                        mirrorStateChangeReceiver = createMirrorStateChangeReceiver(events);
                    }

                    @Override
                    public void onCancel(Object arguments) {
                        mDisplayManager.unregisterDisplayListener(MainActivity.this);
                        mirrorStateChangeReceiver = null;
                    }
                }
        );
    }

    private BroadcastReceiver createMirrorStateChangeReceiver(final EventSink events) {
        return new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                events.success(numberOfDiplay);
            }
        };
    }

    @Override
    public void onDisplayAdded(int displayId) {
        numberOfDiplay = mDisplayManager.getDisplays().length;
    }

    @Override
    public void onDisplayRemoved(int displayId) {
        numberOfDiplay = mDisplayManager.getDisplays().length;
    }

    @Override
    public void onDisplayChanged(int displayId) {
        numberOfDiplay = mDisplayManager.getDisplays().length;
    }
}

这段代码在android上运行良好，我进行了测试，并在屏幕上更新了文本。 现在在《颤栗》中，我创建了一个事件频道，但屏幕上没有任何更新，我不知道为什么

这是dart中的代码

class _PlatformMethodState extends State<PlatformMethod> {
  static const EventChannel eventChannel = EventChannel('com.example.andro/charging');

  String _screenMirror = 'Number of screens: ';


  @override
  void initState() {
    super.initState();
    mirrorChannel.receiveBroadcastStream().listen(_onScreenMirror, onError: _onScreenMirrorError);
  }

  void _onScreenMirror(Object event){
    setState(() {
      _screenMirror =
      "Screen Number: $event.";
    });
  }

  void _onScreenMirrorError(Object error) {
    setState(() {
      _screenMirror = 'Screen Number: unknown.';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Material(
      child: Text(_screenMirror),
    );
  }
}