Question

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问题，即对空值使用的空检查运算符。我收到此错误消息

====== 被手势捕获的异常===================

处理手势时抛出以下_CastError：用于空值的空检查运算符

当抛出异常时，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：GestureDetector 状态：准备好赢得了竞技场 finalPosition: 偏移量(215.0, 716.5) finalLocalPosition: 偏移量(199.0, 16.0) 按钮：1 发送点击＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝

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,
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

Answer 1

这是因为从未分配 _formKey.currentState - 为了分配它，您需要将键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，以不一定会导致您的应用程序崩溃的方式检查表单状态也是一个好主意。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");
  }
}

Flutter 错误，空值检查运算符用于空值

1 个答案: