错误：未定义的名称“isRememberMe”错误：必须提供必需的命名参数“onChanged”

Question

当我尝试定义 isRememberme 小部件时，发生了一些错误。我正在尝试使用颤振和 android studio 构建登录应用程序 UI。我对此很陌生，并且很难找到错误。我已经突出显示了给我错误的代码。

bool isRememberMe =false; //

class LoginScreen extends StatefulWidget {
  @override
  _LoginScreenState createState() => _LoginScreenState();
}

Widget buildEmail() {
  return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
        Text(
          'Email',
          style: TextStyle(
              color: Colors.white,
              fontSize: 16,
              fontWeight:
              FontWeight.bold
          ),
        ),
        SizedBox(height: 10),
        Container(
            alignment: Alignment.centerLeft,
            decoration: BoxDecoration(
                color: Colors.white,
                borderRadius: BorderRadius.circular(10),
                boxShadow: [
                  BoxShadow(
                      color: Colors.black26,
                      blurRadius: 6,
                      offset: Offset(0, 2)
                  )
                ]
            ),

            height: 60,
            child: TextField(
              keyboardType: TextInputType.emailAddress,
              style: TextStyle(color: Colors.black87),
              decoration: InputDecoration(
                  border: InputBorder.none,
                  contentPadding: EdgeInsets.only(top: 14),
                  prefixIcon: Icon(
                    Icons.email,
                    color: Color(0xff5ac18e),
                  ),
                  hintText: 'Email',
                  hintStyle: TextStyle(color: Colors.black38)),
            )
        )
      ],
  );
}

///////////////////////////////

Widget buildPassword() {
  return Column(
    crossAxisAlignment: CrossAxisAlignment.start,
    children: <Widget>[
      Text(
        'Password',
        style: TextStyle(
            color: Colors.white,
            fontSize: 16,
            fontWeight:
            FontWeight.bold
        ),
      ),
      SizedBox(height: 10),
      Container(
          alignment: Alignment.centerLeft,
          decoration: BoxDecoration(
              color: Colors.white,
              borderRadius: BorderRadius.circular(10),
              boxShadow: [
                BoxShadow(
                    color: Colors.black26,
                    blurRadius: 6,
                    offset: Offset(0, 2)
                )
              ]
          ),

          height: 60,
          child: TextField(
            obscureText: true,
            style: TextStyle(color: Colors.black87),
            decoration: InputDecoration(
                border: InputBorder.none,
                contentPadding: EdgeInsets.only(top: 14),
                prefixIcon: Icon(
                  Icons.lock,
                  color: Color(0xff5ac18e),
                ),
                hintText: 'Password',
                hintStyle: TextStyle(color: Colors.black38)),
          )
      )
    ],
  );
}

Widget buildForgotPassBtn(){

  return Container(
    alignment: Alignment.centerRight,
    child: TextButton(
      onPressed: () => print("Forget Password pressed"),
     // padding: EdgeInsets.only(right:0),
      child: Text(
        'Forgot Passsword?',
        style: TextStyle(
          color: Colors.white,
          fontWeight : FontWeight.bold
        ),
      ),
    ),
  );
}

**Widget buildRememberCb(){
  return Container(
    height: 20,
    child: Row(
      children: <Widget>[
       Theme(
          data: ThemeData(unselectedWidgetColor :Colors.white),
          child: Checkbox(
            value: isRememberMe,
             ),
             )
            ],
          ),
        )
}
class _LoginScreenState extends State<LoginScreen> {
  bool isRememberMe =false;**

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: AnnotatedRegion<SystemUiOverlayStyle>(
        value: SystemUiOverlayStyle.light,
        child: GestureDetector(
          child: Stack(
            children: <Widget>[
              Container(
                height: double.infinity,
                width: double.infinity,
                decoration: BoxDecoration(
                    gradient: LinearGradient(
                        begin: Alignment.topCenter,
                        end: Alignment.bottomCenter,
                        colors: [
                          Color(0x665ac18e),
                          Color(0x995ac18e),
                          Color(0xcc5ac18e),
                          Color(0xff5ac18e),
                        ]
                    )
                ),

                child: SingleChildScrollView(
                  physics: AlwaysScrollableScrollPhysics(),
                  padding: EdgeInsets.symmetric(
                    horizontal: 25,
                    vertical: 120,

                  ),

                  child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      Text(
                        'Sign In',
                        style: TextStyle(
                            color: Colors.white,
                            fontSize: 40,
                            fontWeight: FontWeight.bold),
                      ),
                      SizedBox(height: 50),
                      buildEmail(),
                      SizedBox(height: 20),
                      buildPassword(),
                      buildForgotPassBtn(),
                      buildRememberCb(),
                    ],
                  ),
                ),

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

Answer 1

将您的 buildRememberCb 方法移动到您的 _LoginScreenState 类中，以便您可以在 CheckBox 小部件的 on change 方法中使用 setState 方法。

Widget buildRememberCb({bool isRememberMe : false}){
    return Container(
      height: 20,
      child: Row(
        children: <Widget>[
          Theme(
            data: ThemeData(unselectedWidgetColor :Colors.white),
            child: Checkbox(
              value: isRememberMe,
              onChanged: (bool? value) {
                setState((){
                  isRememberMe = value ?? false;
                });
              },
            ),
          )
        ],
      ),
    );

Answer 2

您已在小部件范围之外定义了所有功能。由于 buildRememberCb 函数在作用域之外，所以这里不能访问 isRememberMe 变量。

还需要 Checkbox 小部件的 onChanged 回调。你不能让它未定义。

    class LoginScreen extends StatefulWidget {
  const LoginScreen({Key? key}) : super(key: key);

  @override
  _LoginScreenState createState() => _LoginScreenState();
}

class _LoginScreenState extends State<LoginScreen> {
  bool isRememberMe = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: AnnotatedRegion<SystemUiOverlayStyle>(
        value: SystemUiOverlayStyle.light,
        child: GestureDetector(
          child: Stack(
            children: <Widget>[
              Container(
                height: double.infinity,
                width: double.infinity,
                decoration: const BoxDecoration(
                    gradient: LinearGradient(
                        begin: Alignment.topCenter,
                        end: Alignment.bottomCenter,
                        colors: [
                      Color(0x665ac18e),
                      Color(0x995ac18e),
                      Color(0xcc5ac18e),
                      Color(0xff5ac18e),
                    ])),
                child: SingleChildScrollView(
                  physics: const AlwaysScrollableScrollPhysics(),
                  padding: const EdgeInsets.symmetric(
                    horizontal: 25,
                    vertical: 120,
                  ),
                  child: Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: <Widget>[
                      const Text(
                        'Sign In',
                        style: TextStyle(
                            color: Colors.white,
                            fontSize: 40,
                            fontWeight: FontWeight.bold),
                      ),
                      const SizedBox(height: 50),
                      buildEmail(),
                      const SizedBox(height: 20),
                      buildPassword(),
                      buildForgotPassBtn(),
                      buildRememberCb(),
                    ],
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }

  Widget buildEmail() {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
        const Text(
          'Email',
          style: TextStyle(
              color: Colors.white, fontSize: 16, fontWeight: FontWeight.bold),
        ),
        const SizedBox(height: 10),
        Container(
            alignment: Alignment.centerLeft,
            decoration: BoxDecoration(
                color: Colors.white,
                borderRadius: BorderRadius.circular(10),
                boxShadow: const [
                  BoxShadow(
                      color: Colors.black26,
                      blurRadius: 6,
                      offset: Offset(0, 2))
                ]),
            height: 60,
            child: const TextField(
              keyboardType: TextInputType.emailAddress,
              style: TextStyle(color: Colors.black87),
              decoration: InputDecoration(
                  border: InputBorder.none,
                  contentPadding: EdgeInsets.only(top: 14),
                  prefixIcon: Icon(
                    Icons.email,
                    color: Color(0xff5ac18e),
                  ),
                  hintText: 'Email',
                  hintStyle: TextStyle(color: Colors.black38)),
            ))
      ],
    );
  }

  Widget buildPassword() {
    return Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: <Widget>[
        const Text(
          'Password',
          style: TextStyle(
              color: Colors.white, fontSize: 16, fontWeight: FontWeight.bold),
        ),
        const SizedBox(height: 10),
        Container(
            alignment: Alignment.centerLeft,
            decoration: BoxDecoration(
                color: Colors.white,
                borderRadius: BorderRadius.circular(10),
                boxShadow: const [
                  BoxShadow(
                      color: Colors.black26,
                      blurRadius: 6,
                      offset: Offset(0, 2))
                ]),
            height: 60,
            child: const TextField(
              obscureText: true,
              style: TextStyle(color: Colors.black87),
              decoration: InputDecoration(
                  border: InputBorder.none,
                  contentPadding: EdgeInsets.only(top: 14),
                  prefixIcon: Icon(
                    Icons.lock,
                    color: Color(0xff5ac18e),
                  ),
                  hintText: 'Password',
                  hintStyle: TextStyle(color: Colors.black38)),
            ))
      ],
    );
  }

  Widget buildForgotPassBtn() {
    return Container(
      alignment: Alignment.centerRight,
      child: TextButton(
        onPressed: () => print("Forget Password pressed"),
        // padding: EdgeInsets.only(right:0),
        child: const Text(
          'Forgot Passsword?',
          style: TextStyle(color: Colors.white, fontWeight: FontWeight.bold),
        ),
      ),
    );
  }

  Widget buildRememberCb() {
    return SizedBox(
      height: 20,
      child: Row(
        children: <Widget>[
          Theme(
            data: ThemeData(unselectedWidgetColor: Colors.white),
            child: Checkbox(
              value: isRememberMe,
              onChanged: (bool? value) {
                setState(() {
                  isRememberMe = !isRememberMe;
                });
              },
            ),
          )
        ],
      ),
    );
  }
}