Flutter Fire中如何从DocumentSnapshot获取指定字段并解决StreamBuilder类型报错

错误核心原因 #

• 你调用get()方法获取单文档数据，返回的是Future<DocumentSnapshot>类型，既不是Stream类型，也不是你在StreamBuilder中声明的QuerySnapshot类型
• 要使用Stream做实时监听，需要调用snapshots()方法替代get()
• QuerySnapshot是集合多文档查询的返回类型，你查询的是单个指定uid的文档，返回类型是DocumentSnapshot，两者不能混用

完整修改代码 #

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:quicktodo/model/authservice.dart';

// 修正类名和构造函数命名不匹配的问题
class Analytics extends StatefulWidget {
  const Analytics({Key? key}) : super(key: key);
  String uida = FirebaseAuth.instance.currentUser!.uid;

  @override
  _AnalyticsState createState() => _AnalyticsState();
}

class _AnalyticsState extends State<Analytics> {
  // 明确声明stream类型
  late final Stream<DocumentSnapshot<Map<String, dynamic>>> _stream;
  String uid = FirebaseAuth.instance.currentUser!.uid;

  @override
  void initState() {
    super.initState();
    // 用snapshots()获取实时数据流，替代get()
    _stream = FirebaseFirestore.instance.collection('events').doc(uid).snapshots();
  }

  @override
  Widget build(BuildContext context) {
    final authService = Provider.of<AuthClass>(context);
    return Scaffold(
      appBar: AppBar(
        leading: IconButton(
          icon: const Icon(Icons.logout),
          tooltip: 'List of your activities',
          onPressed: () {
            authService.signout();
          },
        ),
        title: const Text('Activity list'),
        actions: <Widget>[
          IconButton(
            icon: const Icon(Icons.add),
            tooltip: 'List of your activities',
            onPressed: () {},
          ),
        ],
      ),
      // 修正StreamBuilder泛型为DocumentSnapshot
      body: StreamBuilder<DocumentSnapshot<Map<String, dynamic>>>(
        stream: _stream,
        builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot<Map<String, dynamic>>> snapshot) {
          if (snapshot.hasError) {
            return const Text('Something went wrong');
          }
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Text("Loading");
          }
          // 单文档直接取数据，不需要遍历docs列表
          Map<String, dynamic> docData = snapshot.data!.data()!;
          // 如果文档中存储的是活动列表，可以遍历列表字段生成子项，这里以展示eventone字段为例
          return ListView(
            children: [
              Container(
                child: Text(docData['eventone'] ?? ''),
              )
              // 其余要展示的字段可自行添加对应组件
            ],
          );
        },
      ),
    );
  }
}

额外说明 #

如果你不需要实时监听数据变化，只是一次性拉取数据展示，可以把StreamBuilder换成FutureBuilder，_stream变量改为Future<DocumentSnapshot>类型，保持调用get()即可。

内容的提问来源于stack exchange，提问作者akhicoda