flutter - 无法从函数返回类型为 'Stream<dynamic>' 的值，因为它的返回类型为 'Stream<Color>'

Question

迁移到flutter 2后，以下代码段不再起作用:

class ColorBloc extends BlocBase {
// streams of Color
  StreamController _streamListController = StreamController<Color>.broadcast();
// sink
  Sink get colorSink => _streamListController.sink;
// stream
  Stream<Color> get colorStream => _streamListController.stream;


// function to change the color
  changeColor(String chosenColour) {
    switch(chosenColour) {
      case 'blackTheme':
        {
          colorSink.add(AppState.blackTheme);
        }
        break;

      case 'blueTheme':
        {
          colorSink.add(AppState.blueTheme);
        }
        break;

      case 'greenTheme':
        {
          colorSink.add(AppState.greenTheme);
        }
        break;

      case 'redTheme':
        {
          colorSink.add(AppState.redTheme);
        }
        break;

      case 'whiteTheme':
        {
          colorSink.add(AppState.whiteTheme);
        }
        break;
    }

  }

  @override
  dispose() {
    _streamListController.close();
  }
}

问题出在这一行:

 Stream<Color> get colorStream => _streamListController.stream;

给出的理由是:

A value of type 'Stream<dynamic>' can't be returned from the function 'colorStream' because it has a return type of 'Stream<Color>'. 

但我不太确定这意味着什么，或者如何尝试解决它。​​

Answer 1

您只需编辑此行 StreamController _streamListController = StreamController<Color>.broadcast();至StreamController<Color> _streamListController = StreamController<Color>.broadcast();

错误表明 colorStream是 Stream的Color但你给它一个 Stream的dynamic和dynamic可以是任何东西。所以这是一个错误的类型分配。流当然是通用的。