Question

我收到错误type 'List<dynamic>' is not a subtype of type 'String'

错误指向return ChatRoomTile(snapshot.data.documents[index].data['participants']);

有人可以告诉我这是怎么回事吗？

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: header(context, strTitle: "Messages",),
      body: StreamBuilder(
        stream: Firestore.instance.collection('/UserChats').where('participants',arrayContains: currentUser.receiverName).snapshots(),
        builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot){
         if(snapshot.hasData){
           return ListView.builder(
             itemCount: snapshot.data.documents.length,
             itemBuilder: (BuildContext context, int index) {
             return ChatRoomTile(snapshot.data.documents[index].data['participants']);
             //Text(snapshot.data.documents[index].documentID);
            },
           );
         }else{return Text("Loading/Error");}
        },
      ),
      
      //getChatRooms(),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.search),
        onPressed: () {
          Navigator.push(context, MaterialPageRoute(builder: (context) => SearchChat()));
        }
        ),
    );
  }
}

Answer 1

通过用流将产生的类型声明数据，尝试包括StreamBuilder期望的数据类型，如下所示：

StreamBuilder<QuerySnapshot>(
    stream: Firestore.instance.collection('/UserChats').where('participants',arrayContains: currentUser.receiverName).snapshots(),
    builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot){
     if(snapshot.hasData){
       // rest
     }else{return Text("Loading/Error");}
    },
  ),

然后取决于您要在ChatroomTile中显示什么。就像Owczar所说的那样，ChatroomTile将String作为参数。

Answer 2

在我看来，snapshot.data.documents[index].data['participants']是List，而ChatRoomTile的构造方法只接受String。如果我没错，这是一个只有一项的列表，请尝试获取列表的第一项：

ChatRoomTile((snapshot.data.documents[index].data['participants'] as List<String>).first);

'List <dynamic>'类型不是'String'类型的子类型扑动错误

2 个答案: