构建StreamBuilder <DocumentSnapshot>（脏，状态：_StreamBuilderBaseState <DocumentSnapshot）时，抛出NoSuchMethodError

Question

我遇到了错误：

  

NoSuchMethodError被抛出   StreamBuilder（脏，状态：   _StreamBuilderBaseState

我的流生成器​​在使用者中，外观如下：

return Consumer<UserModel>(
        builder: (context, userModel, child) {
      return StreamBuilder<DocumentSnapshot>(
        stream: Firestore.instance.collection(userModel.uid)
            .document(userModel.uid).snapshots(),
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            return Stack(
              children: <Widget>[
                new Container(
                  color: Colors.blue,
                ),
                new Image.network(
                  snapshot.data['photourl'].toString(),
                  fit: BoxFit.fill,
                ),
                new BackdropFilter(
                    filter: new ui.ImageFilter.blur(
                      sigmaX: 6.0,
                      sigmaY: 6.0,
                    ),
                    child: new Container(
                      decoration: BoxDecoration(
                        color: Colors.blue.withOpacity(0.9),
                        borderRadius: BorderRadius.all(Radius.circular(50.0)),
                      ),
                    )),
                new Scaffold(
                    appBar: new AppBar(
                      title: new Text(widget.title),
                      centerTitle: false,
                      elevation: 0.0,
                      backgroundColor: Colors.transparent,
                    ),
                    drawer: new Drawer(
                      child: new Container(),
                    ),
                    backgroundColor: Colors.transparent,
                    body: new Center(
                      child: new Column(
                        children: <Widget>[
                          new SizedBox(
                            height: _height / 12,
                          ),
                          new CircleAvatar(
                            radius: _width < _height ? _width / 4 : _height /
                                4,
                            backgroundImage: NetworkImage(snapshot
                                .data['photourl']),
                          ),
                          new SizedBox(
                            height: _height / 25.0,
                          ),
                          new Text(
                            snapshot.data['name'],
                            style: new TextStyle(
                                fontWeight: FontWeight.bold,
                                fontSize: _width / 15,
                                color: Colors.white),
                          ),
                          new Padding(
                            padding: new EdgeInsets.only(
                                top: _height / 30,
                                left: _width / 8,
                                right: _width / 8),
                          ),
                          new Divider(
                            height: _height / 15,
                            color: Colors.white,
                          ),
                          new Row(
                            children: <Widget>[
                              rowCell(
                                  snapshot.data['totalquestions'], 'Answers'),
                              rowCell(
                                  '£ ${int.parse(
                                      snapshot.data['totalquestions']) * 2}',
                                  'Earned'),
                            ],
                          ),
                          new Divider(
                              height: _height / 15, color: Colors.white),
                        ],
                      ),
                    ),
                ),
              ],
            );
          } else {
            return CircularProgressIndicator();
          }
    });
    });
  }

user_model.dart文件如下所示：

import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';

class UserModel extends ChangeNotifier {

  String uid = 'testuser';
}