Flutter StreamBuilder，类型为超类

Question

也许我的结构错误，所以任何建议都会受到赞赏。

这是我的课程：

class MainClass {
  final String title;
  MainClass({this.title});
}

class SubClass1 extends MainClass {
  final String subClass1Info;
  SubClass1({this.subClass1Info});
}

class SubClass2 extends MainClass {
  final String subClass2Info;
  SubClass2({this.subClass2Info});
}

class SubClass3 extends MainClass {
  final String subClass3Info;
  SubClass3({this.subClass3Info});
}

然后我有一个StreamBuilder：

StreamBuilder<MainClass>(
          stream: _bloc.stream,
          builder: (BuildContext context, AsyncSnapshot<MainClass> snapshot) {

});

SubClass1，SubClass2或SubClass3都可以通过流发送，子Widgets需要知道他们正在处理哪种类型。

我如何最好地实现这一目标？

Answer 1

您可以使用is关键字来检查对象是否是您的任何Classes

                        StreamBuilder<MainClass>(
                  stream: null,
                  builder: (BuildContext context, AsyncSnapshot<MainClass> snapshot) {
                    if (snapshot.hasData) {
                      if (snapshot.data is SubClass1) {
                        final SubClass1 myData = snapshot.data as SubClass1;
                        return Container(
                          child: Text("SubClass1"),
                        );
                      } else if (snapshot.data is SubClass2) {
                        final SubClass2 myData = snapshot.data as SubClass2;
                        return Container(
                          child: Text("SubClass2"),
                        );
                      } else if (snapshot.data is SubClass3) {
                        final SubClass3 myData = snapshot.data as SubClass3;
                        return Container(
                          child: Text("SubClass3"),
                        );
                      }
                    } else {
                      return Center(
                        child: CircularProgressIndicator(),
                      );
                    }
                  })