如何從Cloud Firestore獲取Flutter應用程序的簡單數據？

Question

當我運行時出現以下錯誤。 這些是撲入Firebase的基本代碼。

構建MyHomePage（臟，狀態：MyHomePageState＃b163a）時引發了以下斷言：'package：flutter / src / widgets / text.dart'：失敗的斷言：235行pos 15：'data！= null'：不是

請，有人可以幫我解決這個問題嗎？

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

您有一個帶有空文本的文本小部件。

在這里，您沒有輸入MyHomePage的標題屬性

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),
  ),

為了解決這個問題，像這樣聲明MyHomePage：

MyHomePage(title: "My Home Page")