flutter - 类型 '_StreamHandlerTransformer' 不是类型 'StreamTransformer, dynamic>' 的子类型

Question

当我尝试从 StreamTransform 获取一些数据时遇到一些问题

我不明白什么是正确的数据类型

未捕获的异常:类型错误:“_StreamHandlerTransformer”的实例:“_StreamHandlerTransformer”类型不是“StreamTransformer，动态”类型的子类型>

import 'dart:async';
class Cake{}

class Order{
  String type;
  Order(this.type);
}

void main(){
  final controller = new StreamController();

  final order = new Order('vainilla');

 final baker = StreamTransformer.fromHandlers(
       handleData: (cakeType, sink){
           print(cakeType); 
           if(cakeType == 'chocolate'){
              sink.add(new Cake());
           }else{
             sink.addError("No puedo hacer este pastel");
           }
       } 
 );   

  controller.sink.add(order);
  controller.stream
    .map((resp) =>  { print(resp.type) } ) //maybe the sour of  the problem type is here 
    .transform(baker)
    .listen( (cake) => print('aquí esta su pastel $cake'),
              onError: (err) => print(err) 
           );
}

Answer 1

您需要在 handleData 回调中指定类型。

final baker = StreamTransformer.fromHandlers(
      handleData: (Set cakeType, sink){
        print(cakeType);
        if(cakeType == 'chocolate'){
          sink.add(new Cake());
        }else{
          sink.addError("No puedo hacer este pastel");
        }
      }
  );