从 Flutter 中的 snapshot.data 获取数据为 null

Question

我找不到出现此错误的原因，因为 Firestore 上存储了数据，而且我还处理了可能的异常。 StreamBuilder QuerySnapshot 小部件正在引发异常。我该如何解决这个问题请帮助

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

class AdminScreen extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
    CollectionReference users = FirebaseFirestore.instance.collection('complaints');

    return StreamBuilder<QuerySnapshot>(
        stream: users.snapshots(),
        builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
        if (snapshot.hasError) {
            return Text('Something went wrong');
        }

        if (snapshot.connectionState == ConnectionState.waiting) {
            return Text("Loading");
        }
        
        return ListView(
            children: snapshot.data.docs.map((DocumentSnapshot document) {
            return new ListTile(
                title: new Text(document.data()['Name']),
                subtitle: new Text(document.data()['Complaint']),
            );
        }).toList(),
        );
        },
    );}
}

错误：

A non-null String must be provided to a Text widget.
'package:flutter/src/widgets/text.dart':
Failed assertion: line 370 pos 10: 'data != null'
by StreamBuilder<QuerySnapshot> Widget

Firestore SS:

Answer 1

如果没有给出initialData，StreamBuilder 将发出null 作为第一个事件。为了缓解，您应该先使用snapshot.hasData 检查数据是否为null，然后再尝试读取它，例如：

if(!snapshot.hasData) {
 return Center(child: CircularProgressIndicator()));
}
// from here on you can access the data after you have checked it's not null: