_CastError（用于空值的空檢查運算子）顫動

_CastError（用于空值的空檢查運算子）

錯誤代碼

bool validateAndSave() {
    final form = globalFormKey.currentState;
    if (form.validate()) {
      form.save();
      return true;
    }
    return false;
  }

完整代碼

import 'package:flutter/material.dart';
import 'package:flutter_svg/flutter_svg.dart';
import 'package:thex/components/account_check.dart';
import 'package:thex/components/rounded_button.dart';
import 'package:thex/components/rounded_input_field.dart';
import 'package:thex/components/rounded_password_field.dart';
import 'package:thex/constants.dart';
import 'package:thex/models/login_model.dart';
import 'package:thex/screen/Login/components/background.dart';
// import 'package:thex/screen/home/home_screen.dart';
import 'package:thex/screen/signup/signup_screen.dart';
import 'package:url_launcher/url_launcher.dart';


class Body extends StatelessWidget {
   Body({
    Key? key,
  }) : super(key: key);

  final scaffoldKey = GlobalKey<ScaffoldState>();
  GlobalKey<FormState> globalFormKey = GlobalKey<FormState>();
  LoginRequestModel? requestModel;

  void initState() {
    requestModel = LoginRequestModel();
  }
  

  @override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;
    return Background(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Container(
            margin: EdgeInsets.only(bottom: size.height * 0.04),
            child: const Text(
              "Sign In", 
              style: TextStyle(fontWeight: FontWeight.bold, fontSize: 34, color: kPrimaryColor),
            ),
          ),
          SvgPicture.asset(
            "assets/icons/login.svg", 
            height: size.height * 0.35
          ),
          RoundedInputField(
            validator: (value) => ! value!.contains('@') ? null : 'Invalid Email',
            hintText: "Your Email",
            onSaved: (value) {
              requestModel!.email = value;
            },
          ),
          RoundedPasswordField(
            validator: (password) =>  password!.length < 6 ? 'Password too short' : null,
            hintText: "Your Password",
            onSaved: (password) {
              requestModel!.password = password;
            },
          ),
          RoundedButton(
            text: "LOGIN",
            press: () {
              if (validateAndSave()) {
                print(requestModel!.toJson());
              }
              // Navigator.push(
              //   context,
              //   MaterialPageRoute(
              //     builder: (context) {
              //       return const HomeScreen();
              //     },
              //   ),
              // );
            
            },
          ),
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              AlreadyHaveAnAccountCheck(
                press: () {
                  Navigator.push(
                    context, 
                    MaterialPageRoute(
                      builder: (context){
                        return const SignUpScreen();
                      },
                    ),
                  );
                },
              ),
            ],
          ),
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              const Text("Don't have an account? ", style: TextStyle(color: kPrimaryColor),),
              GestureDetector(
                onTap: () { launch("https://www.web.com/forgot-password");},
                child: const Text("Reset Password", style: TextStyle(color: kPrimaryColor),),
              ),
            ],
          )
        ],
      ),
    );
  }  

  bool validateAndSave() {
    final form = globalFormKey.currentState;
    if (form.validate()) {
      form.save();
      return true;
    }
    return false;
  }
}

幫助！！

uj5u.com熱心網友回復：

你不應該使用“！” 強制不為空。相反， ?? defaultValue在使用“！”之前使用或檢查 null。此外，使用除錯模式 (f5) 檢查流程并了解代碼死在哪里。

uj5u.com熱心網友回復：

我已經改成這樣了，但是控制臺沒有回應。應該有一個列印請求模型

bool validateAndSave() {
        final form = globalFormKey.currentState;
        if (form?.validate != null) {
          form!.save();
          return true;
        } else {
          return false;
        }
      }

uj5u.com熱心網友回復：

問題是您的小部件中沒有表單元素。那里是空的。

您需要使用密鑰添加表單小部件。

@override
  Widget build(BuildContext context) {
    Size size = MediaQuery.of(context).size;
    return Background(
      child: Form(
         key: globalFormKey,
         child: Column(
            ...
         )
      )
   );
} 

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