Flutter我收到了Unvalidated Exception，该方法validate不能调用null

如何解决Flutter我收到了Unvalidated Exception，该方法validate不能调用null

• 我尝试发布http请求以重置密码，并且我将Form小部件与TextFormField一起使用，但是我收到方法validate（）的错误。

• 我用一个键将TextFormField包裹在一个Form中，而且我还在TextFormField中使用了验证器。

• [ERROR：flutter / lib / ui / ui_dart_state.cc（157）]未处理的异常：NoSuchMethodError：方法“ validate”在null上被调用。

• 下面是我用来执行此操作的小部件代码。

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,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,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',labelText: 'New password',textInputAction: TextInputAction.done,onSaved: (value){
                       _newConfirmPassword = value;
                     },decoration: InputDecoration(
                      hintText: 'please retype your new password again',labelText: 'Re-type new password',enabledBorder: OutlineInputBorder(
                       borderRadius: BorderRadius.all(Radius.circular(4)),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',onPressed: (){
                      _resetPassword(code,_newPassword);
                    })
                ],)  
          ],);
  }
}

解决方法

您用相同的名称GlobalKey声明了2个_formKey。一个是State类中的字段，另一个是build方法顶部的字段。

传递到您正在使用的表单的密钥是build中的密钥，因为创建并传递了新密钥，所以每次构建都将其覆盖。

在您的_resetPassword方法中，使用了全班级GlobalKey。该密钥未附加任何内容，因此该范围内的_formKey.currentState为null。这就是导致您异常的原因。

要解决此问题，只需从GlobalKey<FormState> _formKey = GlobalKey();方法的开头删除build。现在将改为使用全班级GlobalKey。