android - Flutter 错误，手势捕获的异常，处理手势时引发以下 _CastError：Null check operator used on a null value
问题描述
每当我尝试登录并点击登录按钮时，我都会遇到用于空值的空检查运算符的此类问题。
这是我收到的错误消息：
════════ 手势捕捉到异常═════════════════════════════════════════════════════════ ═════</p>
The following _CastError was thrown while handling a gesture:
Null check operator used on a null value
When the exception was thrown, this was the stack
#0 _AuthFormState._trySubmit package://FlutterChat/widgets/auth_form.dart:46
#1 _InkResponseState._handleTap
#2 GestureRecognizer.invokeCallback
#3 TapGestureRecognizer.handleTapUp
#4 BaseTapGestureRecognizer._checkUp
Handler: "onTap"
Recognizer: TapGestureRecognizer#c9833
debugOwner: GestureDetector
state: possible
won arena
finalPosition: Offset(165.5, 228.0)
finalLocalPosition: Offset(19.0, 13.5)
button: 1
sent tap down
这是我的 auth_form.dart 文件：
import 'package:flutter/material.dart';
import 'dart:io';
import './user_image_picker.dart';
class AuthForm extends StatefulWidget {
AuthForm(this.submitFn, this.isLoading);
final bool isLoading;
final Future<void> Function(String email, String password, String username,
File image, bool isLogin, BuildContext ctx) submitFn;
@override
_AuthFormState createState() => _AuthFormState();
}
class _AuthFormState extends State<AuthForm> {
final _formKey = GlobalKey<FormState>();
var _isLogin = true;
dynamic _userEmail = '';
dynamic _userName = '';
dynamic _userPassword;
File? _userImageFile;
void _pickedImage(File? image) {
_userImageFile = image;
}
//Form validation and save
_trySubmit() {
final isValid = _formKey.currentState?.validate();
FocusScope.of(context).unfocus();
if (_userImageFile == null && !_isLogin) {
ScaffoldMessenger.of(context).showSnackBar(SnackBar(
content: Text('Please Select an Image'),
backgroundColor: Theme.of(context).errorColor,
));
return;
}
if (isValid!) {
_formKey.currentState?.save();
widget.submitFn(
_userEmail?.trim(),
_userPassword?.trim(),
_userName?.trim(),
_userImageFile!,
_isLogin,
context,
);
}
}
//Form Widget
@override
Widget build(BuildContext context) {
return new Builder(
builder: (context) {
return Center(
child: Card(
margin: EdgeInsets.all(20),
child: SingleChildScrollView(
child: Padding(
padding: EdgeInsets.all(16),
child: Form(
key: _formKey,
child: Column(
children: [
if (!_isLogin) UserImagePicker(_pickedImage),
TextFormField(
key: ValueKey('email'),
autocorrect: false,
textCapitalization: TextCapitalization.none,
enableSuggestions: false,
validator: (value) {
if (value?.isEmpty == null || !value!.contains('@')) {
return 'Please Enter valid Email Address.';
}
return null;
},
keyboardType: TextInputType.emailAddress,
decoration: InputDecoration(
labelText: 'Email Address',
),
onSaved: (value) {
_userEmail = value;
},
),
if (!_isLogin)
TextFormField(
key: ValueKey('username'),
autocorrect: true,
textCapitalization: TextCapitalization.words,
enableSuggestions: false,
validator: (value) {
if (value!.isEmpty) {
return 'Please Enter Username.';
}
return null;
},
decoration: InputDecoration(
labelText: 'Username',
),
onSaved: (value) {
_userName = value;
}),
TextFormField(
key: ValueKey('password'),
validator: (value) {
if (value?.isEmpty == null || value!.length < 7) {
return 'Password must be atleast 7 characters long';
}
return null;
},
obscureText: true,
decoration: InputDecoration(
labelText: 'Password',
),
onSaved: (value) {
_userPassword = value;
}),
SizedBox(
height: 12,
),
if (widget.isLoading) CircularProgressIndicator(),
if (!widget.isLoading)
ElevatedButton(
child: Text(_isLogin ? 'Login' : 'Signup'),
onPressed: _trySubmit,
),
if (!widget.isLoading)
TextButton(
child: Text(_isLogin
? 'Create a new account'
: 'I already have an account'),
style: TextButton.styleFrom(primary: Colors.pink),
onPressed: () {
setState(() {
_isLogin = !_isLogin;
});
},
),
],
),
),
),
),
),
);
},
);
}
}
这是我的 auth_screen.dart 文件：
import 'package:FlutterChat/screens/conversion_screen.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import '../widgets/auth_form.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'dart:io';
import 'package:firebase_storage/firebase_storage.dart';
//import 'package:firebase_core/firebase_core.dart';
class AuthScreen extends StatefulWidget {
@override
_AuthScreenState createState() => _AuthScreenState();
}
class _AuthScreenState extends State<AuthScreen> {
//FirebaseAuth _auth = FirebaseAuth.instance;
var _isLoading = false;
//Submit AuthCredential Function
Future<void> submitAuthForm(String? email, String? password, String? username,
File? image, bool isLogin, BuildContext ctx) async {
UserCredential userCredential;
try {
setState(() {
_isLoading = true;
});
if (isLogin) {
userCredential = await FirebaseAuth.instance
.signInWithEmailAndPassword(email: email!, password: password!);
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => ConversionScreen()));
} else {
userCredential = await FirebaseAuth.instance
.createUserWithEmailAndPassword(email: email!, password: password!);
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => ConversionScreen()));
final ref = FirebaseStorage.instance
.ref()
.child('user_image')
.child(userCredential.user!.uid + '.jpg');
await ref.putFile(image!).whenComplete(() => print('Image Upload'));
final url = await ref.getDownloadURL();
await FirebaseFirestore.instance
.collection('users')
.doc(userCredential.user?.uid)
.set({
'username': username,
'email': email,
'imageUrl': url,
});
}
} on PlatformException catch (error) {
dynamic message = 'An error occured, please check your credentials!';
if (error.message != null) {
message = error.message;
}
ScaffoldMessenger.of(context).showSnackBar(
SnackBar(
content: Text(message),
backgroundColor: Theme.of(ctx).errorColor,
),
);
setState(() {
_isLoading = false;
});
} catch (error) {
print(error);
setState(() {
_isLoading = false;
});
}
}
@override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Theme.of(context).primaryColor,
body: AuthForm(submitAuthForm, _isLoading),
);
}
}
如果有人知道，请帮助我。
解决方案
由于这条线而发生错误，
_userImageFile!,
我怀疑你的if条款，
if (_userImageFile == null && !_isLogin) {
没有保护它不为 not null，因为尽管为空，但如果为真，则该if子句将为假。_isLogin_userImageFile
解决此问题的一种方法是删除bang运算符，因为您也可以submitFn在您_isLogin为真时调用 the ，在这种情况下，您肯定不会有非 null _userImageFile。
_userImageFile, // while calling widget.submitFn
然后确保将“submitFn”函数类型更改为
final Future<void> Function(String email, String password, String username,
// add the ? for File image
File? image, bool isLogin, BuildContext ctx) submitFn;
既然您submitAuthForm已经说过File? image，那里没有什么可改变的。