如何在有状态的小部件中使用键？答案

【问题标题】：How to use keys in stateful widgets?如何在有状态的小部件中使用键？
【发布时间】：2020-07-30 05:47:50
【问题描述】：

我有两个文件，在一个文件中，我有 auth 类，它处理身份验证。

错误处理也在 auth 类中，我所要做的就是将错误传递到登录屏幕，

这是我的身份验证类

Future<FirebaseUser> handleSignInEmail(String email, String password) async {
  

    FirebaseUser user;
    var errorMessage;

    try {
      AuthResult result = await _auth.signInWithEmailAndPassword(
          email: email, password: password);
      user = result.user;
    } catch (error) {
      switch (error.code) {
        case "ERROR_INVALID_EMAIL":
          errorMessage = "Your email address appears to be malformed.";

          break;
        case "ERROR_WRONG_PASSWORD":
          errorMessage = "Your password is wrong.";
          break;
        case "ERROR_USER_NOT_FOUND":
          errorMessage = "User with this email doesn't exist.";
          break;
        case "ERROR_USER_DISABLED":
          errorMessage = "User with this email has been disabled.";
          break;
        case "ERROR_TOO_MANY_REQUESTS":
          errorMessage = "Too many requests. Try again later.";
          break;
        case "ERROR_OPERATION_NOT_ALLOWED":
          errorMessage = "Signing in with Email and Password is not enabled.";
          break;
        default:
          errorMessage = "An undefined Error happened.";
      }
    }

    if (errorMessage != null) {
      Body(
        key: errorMessage,// the error occurs here :(
      );
      return Future.error(errorMessage);
    }

    return user;
  }

这是我的 body 类，我必须将错误传递到其中。

class Body extends StatefulWidget {
  final errorMess;

  Body({Key key, this.errorMess}) : super(key: key);

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

在我的Bodystate中，我有这个功能，

 geterrorMesage() {
    print(widget.errorMess);
  }

当我尝试调用此函数时，发生异常-

参数类型“String”不能分配给参数类型“Key”。

如何解决这个问题？

【问题讨论】：

标签： firebase flutter dart firebase-authentication

【解决方案1】：

您可以在下面复制粘贴运行完整代码
您可以将_key 传递给Body 并使用_key.currentState 调用geterrorMesage

代码sn-p

GlobalKey _key = GlobalKey();

...
final _BodyState _bodyState = _key.currentState;
_bodyState.geterrorMesage("this is test");

...
Body(
          key: _key,
          errorMess: "no error",
        ),
...         
geterrorMesage(String errorMess) {
    print(errorMess);
    setState(() {
      _errorMess = errorMess;
    });
  }

工作演示

完整代码

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  GlobalKey _key = GlobalKey();

  void _incrementCounter() {
    final _BodyState _bodyState = _key.currentState;
    _bodyState.geterrorMesage("this is test");

    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
            Body(
              key: _key,
              errorMess: "no error",
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

class Body extends StatefulWidget {
  final errorMess;
  Body({Key key, this.errorMess}) : super(key: key);

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

class _BodyState extends State<Body> {
  String _errorMess = "";

  geterrorMesage(String errorMess) {
    print(errorMess);
    setState(() {
      _errorMess = errorMess;
    });
  }

  @override
  void initState() {
    super.initState();
    _errorMess = widget.errorMess;
  }

  @override
  Widget build(BuildContext context) {
    return Text("${_errorMess}");
  }
}

【讨论】：