final KeyboardVisibilityController? controller;
  KeyboardVisibilityController get _controller =>      controller ?? KeyboardVisibilityController();
  const KeyboardVisibilityBuilder({    Key? key,    required this.builder,    this.controller,  }) : super(key: key);
  /// A builder method that exposes if the native keyboard is visible.  final Widget Function(BuildContext, bool isKeyboardVisible) builder;
  @override  Widget build(BuildContext context) {    return StreamBuilder<bool>(      stream: _controller.onChange,      initialData: _controller.isVisible,      builder: (context, snapshot) {        if (snapshot.data != null) {          return builder(context, snapshot.data!);        } else {          return builder(context, false);        }      },    );  }

  监听数据回传    static final _onChangeController = StreamController<bool>();  static final _onChange = _onChangeController.stream.asBroadcastStream();    static Stream<bool> get onChange {    // If _testIsVisible set, don't try to create the EventChannel    if (!_isInitialized && _testIsVisible == null) {      _platform.onChange.listen(_updateValue);      _isInitialized = true;    }    return _onChange;  }

export default class FlutterKeyboardVisibilityPlugin implements FlutterPlugin, StreamHandler, AbilityAware {  private eventSink: EventSink | null = null;  private isVisible: boolean = false;  private context: common.Context | null = null;  private window: window.Window | undefined = undefined;
  constructor() {
  }
  getUniqueClassName(): string {    return "FlutterKeyboardVisibilityPlugin"  }
  onAttachedToEngine(binding: FlutterPluginBinding): void {    this.init(binding.getBinaryMessenger());    this.context = binding.getApplicationContext();
  }
  private init(messenger: BinaryMessenger): void {    const eventChannel = new EventChannel(messenger, "flutter_keyboard_visibility");    eventChannel.setStreamHandler(this);  }
  onDetachedFromEngine(binding: FlutterPluginBinding): void {  }
  onAttachedToAbility(binding: AbilityPluginBinding): void {  }
  onDetachedFromAbility(): void {    this.unregisterListener();  }
  onListen(o: ESObject, eventSink: EventSink): void {    this.eventSink = eventSink;    this.listenForKeyboard();  }
  onCancel(o: ESObject): void {    this.eventSink = null;  }
  private async listenForKeyboard(): Promise<void> {    try {      if(this.window == undefined) {        const uiAbility = FlutterManager.getInstance().getUIAbility((getContext(this)));        const windowStage = FlutterManager.getInstance().getWindowStage(uiAbility);        this.window = windowStage.getMainWindowSync();      }      this.window?.on("avoidAreaChange", (data) => {        if (data.type == 3) {          let newState = data.area.bottomRect.height > 0 ? true : false;          if (newState != this.isVisible) {            this.isVisible = newState;            if (this.eventSink != null) {              this.eventSink.success(this.isVisible ? 1 : 0);            }          }        }      });
    } catch (err) {      Log.e(TAG, "Failed to obtain the top window. Cause: " + JSON.stringify(err));    }
  }
  private unregisterListener(): void {    if(this.window != undefined) {      this.window.off("avoidAreaChange", (data) => {        this.window = undefined;      });    }  }}