每当我尝试注册并点击注册按钮时,我都会遇到这种类型的空值检查运算符的问题。我收到了这个错误消息
══════ 异常捕获手势 ════════════════════
在处理手势时引发了以下_CastError:对空值使用空检查运算符
当抛出异常时,这是堆栈
#0\u授权状态。建筑包装:gr_空间/屏幕/配置文件_屏幕。省道:244
#1(香港)地产_handleTap包装:颤振/材料/墨水井。省道:989
#2 GestureRecognizer.invoke回调包:flutter/.../手势/recognizer.dart:182
#3 t手势识别器。手摇
软件包:颤振/../signatures/tap。省道:607
#4 BaseTapgestureRecognitor_检查包:颤振/手势/轻触。省道:296
... 处理程序:“onTap”识别器:TapGestureRecognizer#f8d29调试所有者:GestureDetector状态:就绪赢得竞技场最终位置:偏移(215.0716.5)最终位置:偏移(199.0,16.0)按钮:1发送点击═════════════════════════════════════════════════════════
这是我的授权屏幕。省道锉
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,
),
),
),
],
),
),
),
);
}
}
这是因为\u formKey。currentState
从未分配-为了分配它,您需要将密钥传递给表单小部件,如下所示:
Form(
key: _formKey,
child: ...
)
然后,Form小部件将负责分配当前状态
。
如果_formKState
为空,检查表单状态不一定会导致应用崩溃也是一个好主意ey.current。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");
}
}
E/flatter(26872):[错误:flatter/lib/ui/ui\u dart\u state.cc(199)]未处理的异常:在空值E/flatter(26872)上使用的空检查运算符:#0 MethodChannelFirebaseMessaging。registerBackgroundMessageHandler(包:firebase\u messaging\u platform\
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