Validation 我得到了一个未处理的异常，方法validate不能调用null

我试图发布http请求来重置密码，并使用带有TextFormField的表单小部件来执行此操作，但我得到了一个错误，该方法验证了该错误

我用一个键将TextFormField包装在一个表单中，并且在TextFormField中使用了验证器

[错误：flatter/lib/ui/ui_dart_state.cc157]未处理的异常：NoSuchMethodError:对null调用了方法“validate”

下面是我用来执行该操作的小部件代码

您声明了两个同名的GlobalKeys\u formKey。一个是State类中的字段，另一个位于build方法的顶部

传递给您正在使用的表单的密钥是构建中的密钥，在每个构建中都会覆盖该密钥，因为会创建并传递一个新密钥

在您的_resetPassword方法中，使用类范围的GlobalKey。此键未附加到任何内容，因此该范围中的\u formKey.currentState为null。这就是导致异常的原因

---

要修复此问题，只需删除GlobalKey _formKey=GlobalKey；从构建方法的开始。现在将改用全班的GlobalKey。

是的，谢谢，它已经工作了

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);
                    })
                ],
              ),
              )  
          ],
        ),
      ),
    );
  }
}