Question

我正在使用Flutter在AWS上编写用于用户登录的代码，这是我的代码

我试图用AWS Cognito创建一个登录屏幕

Submit Method
 submit(BuildContext context) async {
    _formKey.currentState.save();
    String message;
    try {
      _user = await _userService.login(_user.email, _user.password);
      message = 'User sucessfully logged in!';
      if (!_user.confirmed) {
        message = 'Please confirm user account';
      }
    } on CognitoClientException catch (e) {
      if (e.code == 'InvalidParameterException' ||
          e.code == 'NotAuthorizedException' ||
          e.code == 'UserNotFoundException' ||
          e.code == 'ResourceNotFoundException') {
        message = e.message;
      } else {
        message = 'An unknown client error occured';
      }
    } catch (e) {
      message = 'An unknown error occurred';
    }
    final snackBar = new SnackBar(
      content: new Text(message),
      action: new SnackBarAction(
        label: 'OK',
        onPressed: () async {
          if (_user.hasAccess) {
            Navigator.pop(context);
            if (!_user.confirmed) {
              Navigator.push(
                context,
                new MaterialPageRoute(
                    builder: (context) =>
                    new ConfirmationScreen(email: _user.email)),
              );
            }
          }
        },
      ),
      duration: new Duration(seconds: 30),
    );

    Scaffold.of(context).showSnackBar(snackBar);
  }

单击按钮，将调用提交方法


                   Container(
                      height: 40.0,
                      child: Material(
                        borderRadius: BorderRadius.circular(20.0),
                        shadowColor: Colors.blueAccent,
                        color: Colors.blue,
                        elevation: 7.0,
                        child: GestureDetector(
                          onTap: () {
                              submit(context);
                          },
                          child: Center(
                            child: Text(
                              'LOGIN',
                              style: TextStyle(
                                  color: Colors.white,
                                  fontWeight: FontWeight.bold,
                                  fontFamily: 'Montserrat'),
                            ),
                          ),
                        ),
                      ),
                    ),

This is the error that I'm seeing on the terminal when I click on the login button

E/flutter (28368): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The method 'save' was called on null.
E/flutter (28368): Receiver: null
E/flutter (28368): Tried calling: save()
E/flutter (28368): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:50:5)
E/flutter (28368): #1      _LoginScreenState.submit (package:flutter_ui_login/main.dart:69:27)
E/flutter (28368): <asynchronous suspension>
E/flutter (28368): #2      _LoginScreenState.build.<anonymous closure> (package:flutter_ui_login/main.dart:196:31)
E/flutter (28368): #3      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:166:24)
E/flutter (28368): #4      TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:240:9)
E/flutter (28368): #5      TapGestureRecognizer.handlePrimaryPointer (package:flutter/src/gestures/tap.dart:177:9)
E/flutter (28368): #6      PrimaryPointerGestureRecognizer.handleEvent (package:flutter/src/gestures/recognizer.dart:436:9)
E/flutter (28368): #7      PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:73:12)
E/flutter (28368): #8      PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:101:11)
E/flutter (28368): #9      _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:221:19)
E/flutter (28368): #10     _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:199:22)
E/flutter (28368): #11     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7)
E/flutter (28368): #12     _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7)
E/flutter (28368): #13     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7)
E/flutter (28368): #14     _rootRunUnary (dart:async/zone.dart:1136:13)
E/flutter (28368): #15     _CustomZone.runUnary (dart:async/zone.dart:1029:19)
E/flutter (28368): #16     _CustomZone.runUnaryGuarded (dart:async/zone.dart:931:7)
E/flutter (28368): #17     _invoke1 (dart:ui/hooks.dart:233:10)
E/flutter (28368): #18     _dispatchPointerDataPacket (dart:ui/hooks.dart:154:5)
E/flutter (28368):

当我单击登录时，在终端上看不到上面的消息，应用程序没有任何变化。我正在为Cognito用户登录到AWS开发一个小型应用程序。如果您的任何人都有不同的AWS登录代码，请帮助我。

Answer 1

我不认识Flutter，我认识Cognito。您似乎收到的错误消息与Cognito无关。

Atom 1.25

重要的部分是E/flutter (28368): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The method 'save' was called on null. E/flutter (28368): Receiver: null，所以当您调用此The method 'save' was called on null方法时，我查看了您的代码，这似乎是您进行的第一个调用，甚至在调用Cognito之前：{{1 }}

因此，您需要了解为什么save()为空。

恕我直言，这不是Cognito问题。

Answer 2

不是Sébastien Stormacq所述的Cognito问题，因为我想象中的Cognito代码没有在您的_userService中被调用。

似乎submit（）方法无法读取_formkey属性。您的commit（）方法是否存在于声明_formkey的State类中？

这是根据Flutter official guide

改编而成的示例结构

// Create a Form widget.
class MyCustomForm extends StatefulWidget {
  @override
  MyCustomFormState createState() {
    return MyCustomFormState();
  }
}

// Create a corresponding State class.
// This class holds data related to the form.
class MyCustomFormState extends State<MyCustomForm> {
  // Create a global key that uniquely identifies the Form widget
  // and allows validation of the form.
  //
  // Note: This is a GlobalKey<FormState>,
  // not a GlobalKey<MyCustomFormState>.
  final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    // Build a Form widget using the _formKey created above.
    return Form(
      key: _formKey,
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: Container(

        // declare your Container layout and your submit button logic here
        // _formkey.currentState will be defined  

        )
  }
}

如何通过AWS Cognito解决错误Flutter登录

2 个答案: