android - Flutter Form:方法 'validate'在null上调用。 [所有配置均已配置]

Question

请帮我!我正在创建简单的登录页面，但出现如下异常:

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY╞════════════════ [+3s] I/flutter (11275): The following NoSuchMethodError was thrown building LoginScreen(dirty, dependencies: [MediaQuery]): [ ] I/flutter (11275): The method 'validate' was called on null. [
] I/flutter (11275): Receiver: null [ ] I/flutter (11275): Tried calling: validate() [ ] I/flutter (11275): [ ] I/flutter (11275): The relevant error-causing widget was: [ ] I/flutter (11275): LoginScreen

虽然我认为，我已经配置了所有需要配置。但是不知何故，我的代码抛出了异常。如何解决？

这是我的代码:

import 'package:flutter/material.dart';
import 'package:flutter_icons/flutter_icons.dart';
import 'package:my_app/services/UserService.dart';

/*
 * This is login screen view.
 * 
 * If you want to edit form section for example email and password fields, just edit these below functions.
 * - _formEmailWidget()
 * - _formPasswordWidget()
 * If you want to edit social login section, just edit _socialLoginWidget() function.
 * If you want to edit or change logo, just edit _logoWidget() function.
 */
class LoginScreen extends StatelessWidget {
  static final Pattern _pattern =
      r'^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$';
  final GlobalKey<FormState> _key = GlobalKey<FormState>();
  final TextEditingController _emailController = TextEditingController();
  final TextEditingController _passwordController = TextEditingController();

  final UserAuth _auth = UserAuth.instance();

  final Status status;

  LoginScreen({@required this.status});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        resizeToAvoidBottomPadding: false,
        body: SafeArea(child: this._bodyWidgets(context)));
  }

  _logoWidget() {
    return Padding(
        padding: const EdgeInsets.only(top: 15.0, bottom: 50.0),
        child: Image(image: AssetImage('assets/images/logo.png')));
  }

  _formEmailWidget() {
    return Container(
        decoration: BoxDecoration(
            border:
                Border(bottom: BorderSide(color: Colors.white, width: 1.0))),
        child: TextFormField(
          controller: _emailController,
          keyboardType: TextInputType.emailAddress,
          validator: (String value) {
            RegExp regex = new RegExp(_pattern);
            if (regex.hasMatch(value)) {
              return null;
            }
            return "Please, Enter valid e-mail";
          },
          decoration: const InputDecoration(
              icon: Icon(
                FontAwesome.user,
                color: Colors.white,
              ),
              fillColor: Colors.white,
              hintStyle: TextStyle(
                color: Colors.white,
                fontFamily: 'ProximaThin',
              ),
              hintText: 'Your e-mail'),
        ));
  }

  _formPasswordWidget() {
    return Container(
        decoration: BoxDecoration(
            border:
                Border(bottom: BorderSide(color: Colors.white, width: 1.0))),
        child: TextFormField(
          controller: _passwordController,
          validator: (String value) {
            if (value.isEmpty || value.length < 6) {
              return "Password must be more than 6 characters";
            }
            return null;
          },
          decoration: const InputDecoration(
              icon: Icon(
                FontAwesome.key,
                color: Colors.white,
              ),
              fillColor: Colors.white,
              hintStyle: TextStyle(
                color: Colors.white,
                fontFamily: 'ProximaThin',
              ),
              hintText: 'Your password'),
          obscureText: true,
        ));
  }

  _submitRowWidget() {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      children: <Widget>[
        InkWell(
          onTap: null,
          child: Text(
            'forget password?',
            style: TextStyle(color: Colors.white),
          ),
        ),
        OutlineButton(
          textColor: Colors.white,
          highlightedBorderColor: Colors.white,
          borderSide: BorderSide(
              color: Colors.white, width: 0.8, style: BorderStyle.solid),
          shape: OutlineInputBorder(borderRadius: BorderRadius.circular(10.0)),
          onPressed: _loginAction(),
          child: Text(
            'Login',
            style: TextStyle(color: Colors.white),
          ),
        )
      ],
    );
  }

  _loginAction() {
    if (_key.currentState.validate()) {
      _auth.signIn(_emailController.text, _passwordController.text);
    } else {
      AlertDialog(
        content: Text(
            "Your e-mail or password doesn't match, Would you like create an account?"),
        elevation: 24.0,
        shape: OutlineInputBorder(borderRadius: BorderRadius.circular(10)),
        actions: <Widget>[
          FlatButton(
            onPressed: null,
            child: Text("Yes"),
          )
        ],
      );
    }
  }

  _socialLoginWidget() {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceBetween,
      children: <Widget>[
        Container(
          decoration: BoxDecoration(
            color: Colors.white,
            borderRadius: BorderRadius.all(Radius.circular(10)),
          ),
          child: FlatButton(
            padding: const EdgeInsets.only(
                left: 10.0, top: 0.0, bottom: 0.0, right: 10.0),
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                Icon(FontAwesome.facebook_f, color: Colors.black),
                SizedBox(
                  width: 10,
                ),
                Text('Facebook',
                    style: TextStyle(
                        fontFamily: 'Proxima',
                        fontSize: 11,
                        color: Colors.black))
              ],
            ),
            onPressed: null,
          ),
        ),
        Container(
          width: 100,
          decoration: BoxDecoration(
            color: Colors.white,
            borderRadius: BorderRadius.all(Radius.circular(10)),
          ),
          child: FlatButton(
            padding: const EdgeInsets.only(
                left: 10.0, top: 0.0, bottom: 0.0, right: 10.0),
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                Icon(
                  FontAwesome.google,
                  color: Colors.black,
                ),
                SizedBox(
                  width: 10,
                ),
                Text(
                  'Google',
                  style: TextStyle(
                      fontFamily: 'Proxima', fontSize: 11, color: Colors.black),
                )
              ],
            ),
            onPressed: null,
          ),
        )
      ],
    );
  }

  _bodyWidgets(BuildContext context) {
    return Column(
        crossAxisAlignment: CrossAxisAlignment.center,
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          _logoWidget(),
          Expanded(
              child: Center(
            child: Container(
              width: MediaQuery.of(context).size.width - 20,
              decoration: BoxDecoration(
                  color: Colors.black,
                  boxShadow: [
                    BoxShadow(
                        color: Color.fromRGBO(0, 0, 0, 0.35),
                        blurRadius: 15.0,
                        offset: Offset(0, -5))
                  ],
                  borderRadius: BorderRadius.only(
                      topLeft: Radius.circular(30),
                      topRight: Radius.circular(30))),
              child: Padding(
                padding:
                    const EdgeInsets.only(top: 45.0, left: 45.0, right: 45.0),
                child: Column(children: <Widget>[
                  Form(
                    key: this._key,
                    child: Column(
                      children: <Widget>[
                        _formEmailWidget(),
                        _formPasswordWidget(),
                        SizedBox(
                          height: 15.0,
                        ),
                        _submitRowWidget()
                      ],
                    ),
                  ),
                  SizedBox(
                    height: 45,
                  ),
                  Text('or connect using',
                      style: TextStyle(
                          fontFamily: 'ProximaThin', color: Colors.white)),
                  SizedBox(
                    height: 15,
                  ),
                  _socialLoginWidget(),
                  SizedBox(
                    height: 15,
                  ),
                  Row(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      Text(
                        'Don\'t have an account?',
                        style: TextStyle(
                            fontFamily: 'ProximaThin', color: Colors.white),
                      ),
                      SizedBox(
                        width: 5,
                      ),
                      InkWell(
                        onTap: null,
                        child: Text('Sign up',
                            style: TextStyle(
                                fontFamily: 'Proxima', color: Colors.white)),
                      )
                    ],
                  )
                ]),
              ),
            ),
          ))
        ]);
  }
}

Answer 1

您在这里有两个选择:

将波纹管方法OnPressed: _loginAction(),更改为OnPressed: _loginAction,

或将同一行更改为OnPressed: () { _loginAction(); },

固定代码如下:

  _submitRowWidget() {
return Row(
  mainAxisAlignment: MainAxisAlignment.spaceBetween,
  children: <Widget>[
    InkWell(
      onTap: null,
      child: Text(
        'forget password?',
        style: TextStyle(color: Colors.white),
      ),
    ),
    OutlineButton(
      textColor: Colors.white,
      highlightedBorderColor: Colors.white,
      borderSide: BorderSide(
          color: Colors.white, width: 0.8, style: BorderStyle.solid),
      shape: OutlineInputBorder(borderRadius: BorderRadius.circular(10.0)),
      onPressed: _loginAction,
      child: Text(
        'Login',
        style: TextStyle(color: Colors.white),
      ),
    )
  ],
);

}