颤振错误,对空值使用空检查运算符
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【中文标题】颤振错误,对空值使用空检查运算符【英文标题】:Flutter error, Null check operator used on a null value 【发布时间】:2021-09-25 08:40:48 【问题描述】:每当我尝试进行注册并点击注册按钮时,我都会遇到用于空值的空检查运算符的此类问题。 我收到此错误消息
══════ 手势捕获的异常════════════════════
在处理手势时引发以下 _CastError: 用于空值的空检查运算符
当异常被抛出时,这是堆栈
#0 _AuthorizationState.build。 包:gr_space/screens/profile_screen.dart:244
#1 _InkResponseState._handleTap 包:flutter/…/material/ink_well.dart:989
#2 GestureRecognizer.invokeCallback 包:flutter/…/gestures/recognizer.dart:182
#3 TapGestureRecognizer.handleTapUp
package:flutter/…/gestures/tap.dart:607
#4 BaseTapGestureRecognizer._checkUp 包:flutter/…/gestures/tap.dart:296
... 处理程序:“onTap” 识别器:TapGestureRecognizer#f8d29 debugOwner:手势检测器 状态:就绪 赢得竞技场 finalPosition: 偏移量(215.0, 716.5) finalLocalPosition: 偏移量(199.0, 16.0) 按钮:1 发送点击向下 ══════════════════════════════════════════════════ ═══════
这是我的身份验证屏幕。飞镖文件
import 'package:flutter/material.dart';
enum AuthMode Signup, Login
class ProfileScreen extends StatelessWidget
static const routeName = '/profile';
@override
Widget build(BuildContext context)
return AnimatedContainer(
duration: Duration(milliseconds: 300),
child: Authorization(),
);
class Authorization extends StatefulWidget
@override
_AuthorizationState createState() => _AuthorizationState();
class _AuthorizationState extends State<Authorization>
final GlobalKey<FormState> _formKey = GlobalKey();
AuthMode _authMode = AuthMode.Login;
final _passwordController = TextEditingController();
Map<String, String> _authData =
'firstName': '',
'lastName': '',
'username': '',
'email': '',
'phoneNumber': '',
'dateOfBirth': '',
'password': '',
'confirmPassword': '',
'city': '',
'gender': '',
;
void _switchAuthMode()
if (_authMode == AuthMode.Login)
setState(()
_authMode = AuthMode.Signup;
);
else
setState(()
_authMode = AuthMode.Login;
);
@override
Widget build(BuildContext context)
final deviceSize = MediaQuery.of(context).size;
return Container(
height: _authMode == AuthMode.Signup ? 320 : 260,
constraints:
BoxConstraints(minHeight: _authMode == AuthMode.Signup ? 620 : 660),
width: deviceSize.width,
padding: EdgeInsets.all(16.0),
child: Form(
child: SingleChildScrollView(
child: Column(
children: [
TextFormField(
decoration: InputDecoration(labelText: 'First name'),
keyboardType: TextInputType.name,
// ignore: missing_return
validator: (value)
if (value!.isEmpty)
return 'Required';
,
onSaved: (value)
_authData['firstName'] = value!;
,
),
TextFormField(
decoration: InputDecoration(labelText: 'Last name'),
keyboardType: TextInputType.emailAddress,
// ignore: missing_return
validator: (value)
if (value!.isEmpty)
return 'Required';
,
onSaved: (value)
_authData['lastName'] = value!;
,
),
TextFormField(
decoration: InputDecoration(labelText: 'Username'),
keyboardType: TextInputType.name,
// ignore: missing_return
validator: (value)
if (value!.isEmpty)
return 'Required';
,
onSaved: (value)
_authData['username'] = value!;
,
),
TextFormField(
decoration: InputDecoration(labelText: 'E-Mail'),
keyboardType: TextInputType.emailAddress,
// ignore: missing_return
validator: (value)
if (value!.isEmpty || !value.contains('@'))
return 'Invalid email!';
,
onSaved: (value)
_authData['email'] = value!;
,
),
TextFormField(
decoration: InputDecoration(labelText: 'Password'),
obscureText: true,
controller: _passwordController,
// ignore: missing_return
validator: (value)
if (value!.isEmpty || value.length < 5)
return 'Password is too short!';
,
onSaved: (value)
_authData['password'] = value!;
,
),
(_authMode == AuthMode.Login)
? Container(
child: Column(children: [
TextFormField(
enabled: _authMode == AuthMode.Signup,
decoration:
InputDecoration(labelText: 'Confirm Password'),
obscureText: true,
validator: _authMode == AuthMode.Signup
// ignore: missing_return
? (value)
if (value != _passwordController.text)
return 'Passwords do not match!';
: null,
onSaved: (value)
_authData['confirmPassword'] = value!;
,
),
TextFormField(
decoration:
InputDecoration(labelText: 'Phone Number'),
keyboardType: TextInputType.phone,
// ignore: missing_return
validator: (value)
if (value!.isEmpty || value.length < 7)
return 'Invalid phone number!';
,
onSaved: (value)
_authData['phone number'] = value!;
,
),
TextFormField(
decoration: InputDecoration(labelText: 'City'),
keyboardType: TextInputType.emailAddress,
// ignore: missing_return
validator: (value)
if (value!.isEmpty)
return 'Required';
,
onSaved: (value)
_authData['city'] = value!;
,
),
TextFormField(
decoration: InputDecoration(labelText: 'Gender'),
keyboardType: TextInputType.emailAddress,
// ignore: missing_return
validator: (value)
if (value!.isEmpty)
return 'Required';
,
onSaved: (value)
_authData['gender'] = value!;
,
),
]),
)
: SizedBox(
height: 10,
),
SizedBox(
height: 20,
),
MaterialButton(
height: 40,
color: Theme.of(context).primaryColor,
minWidth: double.infinity,
onPressed: ()
if(_formKey.currentState!.validate())
print('yess');
,
elevation: 0,
//shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
child: Text(
'Register',
style: TextStyle(
color: Colors.white,
),
),
),
Divider(
color: Colors.black,
),
MaterialButton(
height: 40,
color: Color.fromARGB(255, 222, 82, 69),
minWidth: double.infinity,
onPressed: () ,
elevation: 0,
//shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
child: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Image.asset(
'assets/gmail_logo.png',
height: 25,
width: 25,
),
SizedBox(
width: 15,
),
Text(
'Register with gmail',
style: TextStyle(
color: Colors.white,
),
),
],
),
),
MaterialButton(
height: 40,
color: Color.fromARGB(255, 65, 103, 178),
minWidth: double.infinity,
onPressed: () ,
elevation: 0,
//shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10)),
child: Row(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Image.asset(
'assets/facebook_logo.png',
height: 25,
width: 25,
),
SizedBox(
width: 15,
),
Text(
'Register with Facebook',
style: TextStyle(
color: Colors.white,
),
),
],
),
),
SizedBox(
height: 20,
),
Text(
'Already have an account?',
),
SizedBox(
height: 10,
),
TextButton(
onPressed: _switchAuthMode,
child: Text(
'Sign In',
style: TextStyle(
color: Colors.blue,
decoration: TextDecoration.underline,
),
),
),
],
),
),
),
);
【问题讨论】:
【参考方案1】:这是因为 _formKey.currentState
从未被分配 - 为了分配它,您需要将密钥传递给您的表单小部件,如下所示:
Form(
key: _formKey,
child: ...
)
然后表单小部件将负责分配currentState
。
如果_formKey.currentState
为空,检查表单状态的方式也不会导致您的应用程序崩溃,这也是一个好主意。例如,在您的注册按钮中:
onPressed: ()
if (_formKey.currentState == null)
print("_formKey.currentState is null!");
else if (_formKey.currentState!.validate())
print("Form input is valid");
【讨论】:
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