如何在Flutter应用程序的initState期间使用提供者的数据

Question

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

所需行为：当主屏幕打开时，应用程序应检查用户是否已验证电子邮件，如果未验证，则应显示弹出对话框。

问题：当我通过构造函数传递EmailVerified的数据时，它运行良好，但如果我想使用Provider，我无法在initState()生命周期中获得这些数据。

你能为我推荐这种用例的正确方法吗？

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

您需要使用上下文来调用Provider.of()，这样您就可以添加在第一次构建后调用的addPostFrameCallback()，在那里您可以使用上下文

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

Answer 2

从Provider v4.1.0，您也可以使用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

您可以按如下方式制作initState：

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

Answer 4

您还可以将context传递给HomeScreen小部件，它将允许您访问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 5

为此，我们需要绑定小部件。所以提供商也给我们这个功能

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

Answer 6

在3.0.0+1版本中，您也可以执行

你可以用

var CallNotifier auth;

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