Issue
Whenever I tried to do register and tap on the register button then I am having this type of problem with the null check operator used on null values.
I get this error message
══════ Exception caught by gesture ════════════════════
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 _AuthorizationState.build.
package:gr_space/screens/profile_screen.dart:244
#1 _InkResponseState._handleTap
package:flutter/…/material/ink_well.dart:989
#2 GestureRecognizer.invokeCallback
package:flutter/…/gestures/recognizer.dart:182
#3 TapGestureRecognizer.handleTapUp
package:flutter/…/gestures/tap.dart:607
#4 BaseTapGestureRecognizer._checkUp
package:flutter/…/gestures/tap.dart:296
…
Handler: "onTap"
Recognizer: TapGestureRecognizer#f8d29
debugOwner: GestureDetector
state: ready
won arena
finalPosition: Offset(215.0, 716.5)
finalLocalPosition: Offset(199.0, 16.0)
button: 1
sent tap down
═════════════════════════════════════════════════════════
this is my auth screen. dart file
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,
),
),
),
],
),
),
),
);
}
}
Solution
It’s because _formKey.currentState is never assigned – in order for it to be assigned, you need to pass the key to your Form widget, like so:
Form(
key: _formKey,
child: ...
)
The Form widget will then take care of assigning currentState.
It would also be a good idea to check the form state in a way that won’t necessarily crash your app if _formKey.currentState is null. For example, in your Register button:
onPressed: () {
if (_formKey.currentState == null) {
print("_formKey.currentState is null!");
} else if (_formKey.currentState!.validate()) {
print("Form input is valid");
}
}
Answered By – Michael Horn
Answer Checked By – David Marino (FlutterFixes Volunteer)