firebase - 如何访问Future方法中存在的回调函数的返回值。 Dart

Question

auth.dart

class AuthService {

  final FirebaseAuth _auth = FirebaseAuth.instance;

  // Sign in with Phone Number Future<bool>
  Future signInWithPhone(String phone, BuildContext context) async {

    final PhoneVerificationCompleted verificationCompleted = (AuthCredential credential) async {
      ..
    };

    final PhoneVerificationFailed verificationFailed = (AuthException exception) {
      // This is the return value which i want to access outside of this callback
      return exception.message;
    };

    final PhoneCodeSent codeSent = (String verificationId, [int forceResendingToken]) {
        ...
    };

    final PhoneCodeAutoRetrievalTimeout codeAutoRetrievalTimeout = (String verificationId) {
        Navigator.of(context).pop();
        ...
    };

    await _auth.verifyPhoneNumber(
      phoneNumber: phone,
      timeout: Duration(seconds: 10),
      verificationCompleted: verificationCompleted,
      verificationFailed: verificationFailed,        
      codeSent: codeSent,
      codeAutoRetrievalTimeout: codeAutoRetrievalTimeout
    );

    // Trying to access the callback value
    print(verificationFailed);
 }
}

login.dart

class LoginPage extends StatefulWidget {
  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {

  @override
  Widget build(BuildContext context) {
    return Container(

     // here i am calling the phonesign in method
      await _auth.signInWithPhone(phoneNumber, context);

     // and here i want to show the message

    );
  }

}

有什么问题？

问题是我想访问 verifyPhoneNumber 的任何回调的值，例如 verifyFailed ，它返回异常消息，并且我想在外部访问它，以便可以在其他小部件中使用它。

我到目前为止尝试了什么？

1)我尝试打印它，它返回 AuthException闭包:()=>字符串我不知道如何访问该值。

2)我尝试使用 setState ，但是由于我的类(class)不在 statefulWidget 内，所以我无法将该值分配给变量

*我为什么需要它？ *

看我有两个页面，一个叫做 login.dart，第二个叫做 auth.dart。在我的身份验证页面中，我主要放置与后端相关的类和代码(以正确组织代码)，而在登录页面中，我有一个有状态的小部件，电话文本字段并提交后，我会调用 signInWithPhone 方法。一切正常，但是如果出现任何错误(例如用户电话号码格式错误)，则会触发 VerificationFailed 回调，因此我想在外部访问返回值(bcz我们无法直接获取返回值)，这样我就可以从调用它的地方显示它。

谁能帮助我，以便我继续我的代码。

Answer 1

现在很清楚您要做什么。使用提供程序是一种方法。另一种方法是将回调传递给登录页面:

class LoginPage extends StatefulWidget {
      final Function(String) verificationMessage;

      const LoginPage({Key key, this.verificationMessage}) : super(key: key);

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

class _LoginPageState extends State<LoginPage> {
    …
    …
    final PhoneVerificationFailed verificationFailed = (AuthException exception) {

       widget.verificationMessage(exception.message);’
    };
}

现在，只要您调用LoginPage，就只需传递一个回调函数

LoginPage(verificationMessage: (String message) => {
    setState(() {
        // Do what you want with the message
    })
})

在您的情况下:

验证码

class AuthService {

  **final Function(String) verificationMessage;**
  **AuthService({@required this.verificationMessage});**

  final FirebaseAuth _auth = FirebaseAuth.instance;

  // Sign in with Phone Number Future<bool>
  Future signInWithPhone(String phone, BuildContext context) async {

    final PhoneVerificationCompleted verificationCompleted = (AuthCredential credential) async {
      ..
    };

    final PhoneVerificationFailed verificationFailed = (AuthException exception) {
      // This is the return value which i want to access outside of this callback
       **verificationMessage(exception.message);**
    };

    final PhoneCodeSent codeSent = (String verificationId, [int forceResendingToken]) {
        ...
    };

    final PhoneCodeAutoRetrievalTimeout codeAutoRetrievalTimeout = (String verificationId) {
        Navigator.of(context).pop();
        ...
    };

    await _auth.verifyPhoneNumber(
      phoneNumber: phone,
      timeout: Duration(seconds: 10),
      verificationCompleted: verificationCompleted,
      verificationFailed: verificationFailed,        
      codeSent: codeSent,
      codeAutoRetrievalTimeout: codeAutoRetrievalTimeout
    );

    // Trying to access the callback value
    print(verificationFailed);
 }
}

login.dart

class LoginPage extends StatefulWidget {
  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {

  String message = "";

  @override
  Widget build(BuildContext context) {
    return Container(
         child: Column( 
          children: [
            Text(message),
            Flatbutton(
              .... 
              onPressed: (){
               AuthService(verificationMessage: (String newMessage) => {
                 setState(() {
                   message = newMessage
                 })
               })
              }
            )
          ]
         )
    );
  }



}