Flutter：如何将数据从 `Stream<Foo?>` 过滤到 `Stream<Foo>`

Question

我需要在我的插件中从 EventChannel 创建一个新的Stream<Foo>，我尝试这样做，但我有Stream<Foo?>，我要做的就是过滤所有空值并返回为Stream<Foo>

  Stream<Foo> get getStream {
    return _eventChannel
        .receiveBroadcastStream()
        .map<Foo?>((dynamic status) {
      assert(
      status is int,
      'status should be int, but it is ${status.runtimeType}',
      );
      if (status is int) {
        return FooStatus.valueOf(status); // can be null
      }
    }).helpMeFiltredLikeThis<Foo>((Foo? value) => value != null); // how i can do some like this
  }

Answer 1

你可以像这样在末尾使用cast：

final nonNullableStream = nullableStream.cast<Foo>();