如何从Cloud Firestore获取Flutter应用程序的简单数据？

Question

当我运行时出现以下错误。 这些是扑入Firebase的基本代码。

构建MyHomePage（脏，状态：MyHomePageState＃b163a）时引发了以下断言：'package：flutter / src / widgets / text.dart'：失败的断言：235行pos 15：'data！= null'：不是

请，有人可以帮我解决这个问题吗？

import 'dart:async';

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

Future<void> main() async {
  final FirebaseApp app = await FirebaseApp.configure(
    name: 'vscodefirebase',
    options: const FirebaseOptions(
      googleAppID: 'xxx',
      gcmSenderID: 'xxx',
      apiKey: 'xxxx',
      projectID: 'vscodefirebase',
    ),
  );
  final Firestore firestore = Firestore(app: app);
  await firestore.settings(timestampsInSnapshotsEnabled: true);

  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Firebase',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: StreamBuilder<QuerySnapshot>(
        stream: Firestore.instance.collection('books').snapshots(),
        builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
          if (!snapshot.hasData) return new Text('Loading...');
          return new ListView(
            children: snapshot.data.documents.map((DocumentSnapshot document) {
              return new ListTile(
                title: new Text(document['title']),
                subtitle: new Text(document['author']),
              );
            }).toList(),
          );
        },
      ),
    );
  }
}

Answer 1

您有一个带有空文本的文本小部件。

在这里，您没有输入MyHomePage的标题属性

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Firebase',
      home: MyHomePage(),
    );
  }
}

因此，此“文本”小部件具有空文本值。

  appBar: AppBar(
    title: Text(widget.title),
  ),

为了解决这个问题，像这样声明MyHomePage：

MyHomePage(title: "My Home Page")