Flutter 我得到了未處理的異常，即方法驗證無法調用 null

Question

• 我嘗試發布 http 請求以重置密碼，並且我使用帶有 TextFormField 的表單小部件來執行此操作，但我收到方法 validate() 的錯誤。

• 我用一個鍵將 TextFormField 包裝在一個表單中，我也在 TextFormField 中使用了驗證器。

• [錯誤：flutter/lib/ui/ui_dart_state.cc(157)] 未處理的異常：NoSuchMethodError：在 null 上調用了方法“驗證”。

• 下面是我用來執行該操作的小部件代碼。

import 'dart:io';

import 'package:Zabatnee/common_app/provider/user_details_provider.dart';
import 'package:Zabatnee/common_app/screens/signup_screen.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

class ResetPassword extends StatefulWidget {
  static const routeName = '/resetCode';

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

class _ResetPasswordState extends State<ResetPassword> {
  final GlobalKey<FormState> _formKey = GlobalKey();
String code, _newPassword, _newConfirmPassword;
  var _isLoading = false;

  _showDialog(String title, String message, [bool navigate = false]) {
    showDialog(
      barrierDismissible: false,
      context: context,
      builder: (ctx) => WillPopScope(
        onWillPop: () async => false,
        child: new AlertDialog(
          elevation: 15,
          shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.all(Radius.circular(8))),
          title: Text(
            title,
            style: TextStyle(color: Colors.white),
          ),
          content: Text(
            message,
            style: TextStyle(color: Colors.white),
          ),
          backgroundColor: Theme.of(context).primaryColor,
          actions: <Widget>[
            FlatButton(
              child: Text(
                'OK',
                style: TextStyle(color: Theme.of(context).accentColor),
              ),
              onPressed: () {
                Navigator.of(context).pop();
                setState(
                  () {
                    _isLoading = false;
                  },
                );
                if (navigate) {
                  Navigator.of(context).pushNamed(SignupScreen.routeName);                 
                }
              },
            )
          ],
        ),
      ),
    );
  }

  void _removeFocus (){
   FocusScopeNode currentFocus = FocusScope.of(context);
   if(!currentFocus.hasPrimaryFocus){
     currentFocus.unfocus();
   }

  }
  Future<void> _resetPassword(String userCode, String userNewPassword) async{
    _removeFocus();
    final _isValid = _formKey.currentState.validate();
    if(!_isValid){
      return null;
    }
    _formKey.currentState.save();

    setState(() {
      _isLoading = true;
    });
    try{
      await Provider.of<UserDetailsProvider>(context, listen: false).resetPassword(userCode, userNewPassword);
      _showDialog('Congartulations', 'Account has been created successfully.', true);
    }on HttpException catch (error) {
      _showDialog('Authentication Failed', error.message);
    } on SocketException catch (_) {
      _showDialog('An error occured',
          'please check your internet connection and try again later');
    } catch (error) {
      _showDialog('Authentication Failed',
          'Something went wrong, please try again later');
    }
    setState(() {
      _isLoading = false;
    });
  }

  @override
  Widget build(BuildContext context) {
    GlobalKey<FormState> _formKey = GlobalKey();
    final _newPasswordFocusNode = FocusNode();
    final _confirmPasswordFocusNode = FocusNode(); 
    
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.transparent,
        centerTitle: true,
        title: Text('Reset Password'),
      ),
      backgroundColor: Colors.transparent,
      body: Container(
        margin: EdgeInsets.all(20),
        padding: EdgeInsets.all(16),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            Text(
              'Please enter new password', 
              style: TextStyle(color:Colors.white, fontWeight: FontWeight.bold, fontSize: 20),             
              ),
              SizedBox(
                height: 30,
              ),
            Form(
              key: _formKey,
              child: Column(
                children: <Widget>[
                  TextFormField(
                   decoration: InputDecoration(
                      hintText: 'please enter reset code (check your email)',
                      focusColor: Theme.of(context).primaryColor,
                      fillColor: Colors.white,
                      labelText: 'Reset Code',
                      hintStyle: TextStyle(color:Colors.grey),
                      labelStyle: TextStyle(color:Colors.white),
                      enabledBorder: OutlineInputBorder(
                  borderRadius: BorderRadius.all(Radius.circular(4)),
                  borderSide: BorderSide(width: 1, color: Colors.grey),
                ),
                border: OutlineInputBorder(
                    borderSide:
                        BorderSide(color: Theme.of(context).primaryColor)),
                    ),
                   textInputAction: TextInputAction.next,
                    style: TextStyle(color:Colors.white),
                    onFieldSubmitted: (_){
                      FocusScope.of(context).requestFocus(_newPasswordFocusNode);
                    },
                    validator: (value){
                      if (value.isEmpty) {
                        return 'please enter a valid code';
                      }
                      return null;
                    },
                    onSaved: (value){
                      code = value;
                    },
                      
                  ),
                  SizedBox(
                    height: 15,
                  ),
                   TextFormField(
                     keyboardType: TextInputType.visiblePassword,
                     textInputAction: TextInputAction.next,
                     style: TextStyle(color:Colors.white),
                     onFieldSubmitted: (_){
                       FocusScope.of(context).requestFocus(_confirmPasswordFocusNode);
                     },
                     validator: (value){
                       if(value.length<6){
                         return 'please enter password lager that 6 character';
                       }
                       return null;
                     },
                     onSaved: (value){
                       _newPassword = value;
                     },
                    decoration: InputDecoration(
                      hintText: 'please enter your password',
                      focusColor: Theme.of(context).primaryColor,
                      fillColor: Colors.white,
                      labelText: 'New password',
                      hintStyle: TextStyle(color:Colors.grey),
                      labelStyle: TextStyle(color:Colors.white),
                      enabledBorder: OutlineInputBorder(
                  borderRadius: BorderRadius.all(Radius.circular(4)),
                  borderSide: BorderSide(width: 1, color: Colors.grey),
                ),
                border: OutlineInputBorder(
                    borderSide:
                        BorderSide(color: Theme.of(context).primaryColor)),
                    ),
                  ),
                  SizedBox(
                    height: 15,
                  ),
                   TextFormField(
                     keyboardType: TextInputType.visiblePassword,
                     textInputAction: TextInputAction.done,
                     style: TextStyle(color:Colors.white),
                     onFieldSubmitted: (_){
                       FocusScope.of(context).requestFocus(_confirmPasswordFocusNode);
                     },
                     validator: (value){
                       if(value.length<6){
                         return 'please enter password lager that 6 character';
                       }
                       return null;
                     },
                     onSaved: (value){
                       _newConfirmPassword = value;
                     },
                    decoration: InputDecoration(
                      hintText: 'please retype your new password again',
                      focusColor: Theme.of(context).primaryColor,
                      fillColor: Colors.white,
                      labelText: 'Re-type new password',
                      hintStyle: TextStyle(color:Colors.grey),
                      labelStyle: TextStyle(color:Colors.white),
                      enabledBorder: OutlineInputBorder(
                       borderRadius: BorderRadius.all(Radius.circular(4)),
                       borderSide: BorderSide(width: 1, color: Colors.grey[100]),
                        ),
                      border: OutlineInputBorder(
                        borderSide:
                        BorderSide(color: Theme.of(context).primaryColor)),
                         ),
                  ),
                  SizedBox(
                    height: 30,
                  ),
                  if(_isLoading)
                  CircularProgressIndicator(
                    backgroundColor: Theme.of(context).primaryColor,
                  ),
                  if(!_isLoading)
                  RaisedButton(
                    child: Text('Reset', style: TextStyle(color:Colors.white, fontSize: 20),),
                    onPressed: (){
                      _resetPassword(code, _newPassword);
                    })
                ],
              ),
              )  
          ],
        ),
      ),
    );
  }
}

Answer 1

您在同名GlobalKey下聲明了 2 個_formKey 。 一個是State class 中的一個字段，另一個在build方法的頂部。

傳遞給您正在使用的表單的密鑰是build中的密鑰，它在每次構建時都會被覆蓋，因為會創建並傳遞一個新密鑰。

在您的_resetPassword方法中，使用了類范圍的GlobalKey 。 此密鑰未附加到任何內容，因此_formKey.currentState中的 scope 是null 。 這就是導致您的異常的原因。

要修復，只需刪除GlobalKey<FormState> _formKey = GlobalKey(); 從您的build方法開始。 現在將使用類范圍的GlobalKey 。