我正在尝试为新的flutter应用程序构建一个简单的登录页面。小部件树非常基本。它由包含支架的MaterialApp组成。脚手架的“主页”是一个StatefulWidget,其中包含具有两个TextFormField的Form。
TextFormFields具有“验证器”代码以检查空值。
有一个按钮,当按下该按钮时会调用方法'validateAndSave'。在此方法内部,我正在为GlobalKey的实例调用“验证”方法。
单击按钮时,验证器似乎没有触发,并且我收到以下错误消息:
I/flutter (10459): ══╡ EXCEPTION CAUGHT BY GESTURE ╞═══════════════════════════════════════════════════════════════════
I/flutter (10459): The following NoSuchMethodError was thrown while handling a gesture:
I/flutter (10459): The method 'validate' was called on null.
I/flutter (10459): Receiver: null
I/flutter (10459): Tried calling: validate()
I/flutter (10459):
I/flutter (10459): When the exception was thrown, this was the stack:
I/flutter (10459): #0 Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:50:5)
I/flutter (10459): #1 _LoginForm.validateAndSave (package:playground/main.dart:33:13)
我尝试在项目上运行Flutter Clean,然后重新运行应用程序。我仍然收到错误消息。
这是我正在运行的代码。
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Playground',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Scaffold(body:LoginForm()
),
);
}
}
class LoginForm extends StatefulWidget {
@override
State<StatefulWidget> createState() => _LoginForm();
}
class _LoginForm extends State<LoginForm>{
// GlobalKey<FormState> formKey = new GlobalKey();
final _formKey = new GlobalKey<FormState>();
String _email;
String _password;
void validateAndSave(){
final form = _formKey.currentState;
if(form.validate())
{
print ('Form is valid');
}
else
{
print('form is invalid');
}
}
@override
Widget build(BuildContext context) {
return Container(
padding: EdgeInsets.only(left: 15.0, right: 15.0),
child: Form(
child: Column(
// mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
SizedBox(height: 150.0,),
//input field for email
TextFormField(
decoration: InputDecoration(labelText: 'Email'),
validator: (value) => value.isEmpty ? 'Email cannot be blank':null,
// onSaved: (value) => _email = value,
),
//input field for password
TextFormField(
decoration: InputDecoration(labelText: 'Password'),
obscureText: true,
validator: (value) => value.isEmpty ? 'Password cannot be blank':null,
// onSaved: (value) => _password = value,
),
RaisedButton(
child: Text ('Login', style: TextStyle(fontSize: 20.0),),
onPressed: validateAndSave,
)
]
)
)
);
}
}
我觉得我错过了代码中的某些内容。希望能为您解决此问题提供帮助。
答案 0 :(得分:3)
如果有人也有同样的错误,甚至添加了密钥,那么您的结构就是:
Form => ListView => [TextFormField(s)],
尝试更改结构:
Form => SingleScrollView =>列
此更改对我有用。
快乐的编码。
答案 1 :(得分:1)
您没有将密钥添加到表单中,此代码应该可以工作
class _LoginForm extends State<LoginForm>{
// GlobalKey<FormState> formKey = new GlobalKey();
final _formKey = new GlobalKey<FormState>();
String _email;
String _password;
void validateAndSave(){
final form = _formKey.currentState;
if(form.validate())
{
print ('Form is valid');
}
else
{
print('form is invalid');
}
}
@override
Widget build(BuildContext context) {
return Container(
padding: EdgeInsets.only(left: 15.0, right: 15.0),
child: Form(
key: _formKey,
child: Column(
// mainAxisAlignment: MainAxisAlignment.center,
crossAxisAlignment: CrossAxisAlignment.stretch,
children: <Widget>[
SizedBox(height: 150.0,),
//input field for email
TextFormField(
decoration: InputDecoration(labelText: 'Email'),
validator: (value) => value.isEmpty ? 'Email cannot be blank':null,
// onSaved: (value) => _email = value,
),
//input field for password
TextFormField(
decoration: InputDecoration(labelText: 'Password'),
obscureText: true,
validator: (value) => value.isEmpty ? 'Password cannot be blank':null,
// onSaved: (value) => _password = value,
),
RaisedButton(
child: Text ('Login', style: TextStyle(fontSize: 20.0),),
onPressed: validateAndSave,
)
]
)
)
);
}
}