如何在 Flutter 应用程序的 initState 期间使用来自 Provider 的数据

Question

我正在通过添加 Provider 作为状态管理来重构我的 Flutter 应用程序代码。

期望行为：当主屏幕打开时，应用程序应检查用户的电子邮件是否已验证，如果未验证，则应显示对话框弹出窗口。

问题：当我通过构造函数为 EmailVerified 传递数据时它工作正常，但如果我想使用 Provider，我无法在 initState() 生命周期获取此数据。

您能否推荐我针对此类用例的正确方法？

import 'package:myapp/services/authentication.dart';
import 'package:myapp/screens/settings_screen.dart';
import 'package:flutter/material.dart';
import 'package:myapp/services/authentication.dart';
import 'package:provider/provider.dart';

class HomeScreen extends StatefulWidget {

  @override
  State<StatefulWidget> createState() => new _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  final GlobalKey<FormState> formKey = GlobalKey<FormState>();
  bool _isEmailVerified = false;

  @override
  void initState() {
    super.initState();
    _checkEmailVerification(); // <=== Method which should show Dialog box if email is not verified which is coming from "Auth" Provider
  }

  @override
  Widget build(BuildContext context) {
    final auth = Provider.of<Auth>(context, listen: false); // <==== Service from Provider, which contains data for _isEmailVerified
    auth.isEmailVerified().then((value) => _isEmailVerified = value);

    return new Scaffold(
      appBar: new AppBar(
        title: new Text('My App'),
      ),
      body: Center(
        child: Column(
          children: <Widget>[
            Text(
              'Welcome to my app',
            ),
          ],
        ),
      ),
    );
  }

  void _checkEmailVerification() async {
    _isEmailVerified = auth.isEmailVerified(); // <=== How can I use "auth" from Provider to get isEmailVerified data ????
    if (!_isEmailVerified) {
      _showVerifyEmailDialog();
    }
  }

  void _showVerifyEmailDialog() {
    showDialog(
      context: context,
      builder: (BuildContext context) {
        // return object of type Dialog
        return AlertDialog(
          title: new Text("Verify your account"),
          content: new Text("Please verify account in the link sent to email"),
          actions: <Widget>[
            new FlatButton(
              child: new Text("Resend link"),
              onPressed: () {
                Navigator.of(context).pop();
                _resentVerifyEmail();
              },
            ),
            new FlatButton(
              child: new Text("Dismiss"),
              onPressed: () {
                Navigator.of(context).pop();
              },
            ),
          ],
        );
      },
    );
  }

  void _resentVerifyEmail() {
    // Logic to send email
  }
}

Answer 1

你需要使用上下文来调用Provider.of()，所以你可以添加addPostFrameCallback()在第一次构建之后调用，你可以使用上下文

@override
void initState() {
    super.initState();

    WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
      auth = Provider.of<Auth>(context, listen: false);
    });
}

Answer 2

从Provider v4.1.0，你也可以使用read()方法。它减少了样板代码。

@override
void initState() {
  super.initState();

  WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
    auth = context.read<Auth>();
  });
}

Answer 3

您也可以将context 传递给HomeScreen 小部件，这样您就可以访问Provider：

class HomeScreen extends StatefulWidget {
  final BuildContext context;
  HomeScreen(this.context);

  @override
  State<StatefulWidget> createState() => new _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  bool _isEmailVerified = false;

  void _checkEmailVerification() async {
    _isEmailVerified = widget.context.read<Auth>().isEmailVerified();
    if (!_isEmailVerified) {
      _showVerifyEmailDialog();
    }
  }

...

}

Answer 4

您可以按如下方式设置您的 initState：

''''
 @override
    void initState() {
       super.initState();
       final myModel = Provider.of<YourProivder>(context, listen: false);
  }
''''

Answer 5

在3.0.0+1版本中，你也可以这样做

你可以这样做

var CallNotifier auth;


@override
void initState(){
 super.initState();
 auth = Provider.of<CallNotifier>(context, listen = false);
}