ERROR: The argument type 'Object?' can't be assigned to the parameter type 'String?'

Question

我有一个 TextFormField 小部件包裹在 StreamBuilder 中，在 TextFormField 小部件中，在装饰中，当将 snapshot.error 传递给 errorText 参数时，它给出了一个错误：

参数类型'Object?'无法赋值给参数类型'String?'

这是带有表单和 TextFormField

的状态 class 的代码

class LoginScreen extends StatefulWidget{
  State<StatefulWidget> createState() {
    return _LoginScreen();
  }
}

class _LoginScreen extends State<LoginScreen>{
  final form_key = GlobalKey<FormState>();

  Widget build(context){
    return Container(
      margin: EdgeInsets.all(20),

      child: Form(
        key: form_key,

        child: Column(
          children: [
            emailField(),
            passwordField(),
            Padding(
              padding: EdgeInsets.all(7),

              child: submitButton(),
            ),
            Padding(
              padding: EdgeInsets.all(7),

              child: ResetButton(),
            )
          ],
        ),
      ),
    );
  }

  Widget emailField(){
    return StreamBuilder(
      stream: bloc.email,

      builder: (context, snapshot){
        return TextFormField(
          decoration: const InputDecoration(
            labelText: 'Email',

            errorText: snapshot.error,
          ),

          keyboardType: TextInputType.emailAddress,

          onChanged: bloc.changeEmail,
        );
      },
    );
  }

  Widget passwordField(){
    return StreamBuilder(
      stream: bloc.pass,

      builder: (context, snapshot){
        return TextFormField(
          decoration: const InputDecoration(
            labelText: 'Password'
            
            errorText: snapshot.error,
          ),

          obscureText: true,
        );
      },
    );
  }

  Widget submitButton(){
    return ElevatedButton(
      child: Text('SUBMIT'),

      style: ButtonStyle(
        backgroundColor: MaterialStateProperty.resolveWith(getColor),
      ),

      onPressed: (){},
    );
  }

  Widget ResetButton(){
    return ElevatedButton(
      child: Text('RESET'),

      style: ButtonStyle(
        backgroundColor: MaterialStateProperty.resolveWith(getColor),
      ),
      
      onPressed: (){
        form_key.currentState!.reset();
      }
    );
  }  

  Color getColor(Set<MaterialState> states) {
    const Set<MaterialState> interactiveStates = <MaterialState>{
      MaterialState.pressed,
      MaterialState.hovered,
      MaterialState.focused,
    };
    if (states.any(interactiveStates.contains)) {
      return Colors.orange.shade600;
    }
    return Colors.blue.shade400;
  }
}

我的区块代码class:

class Bloc with Validators{
  final _email = StreamController<String?>();
  final _pass = StreamController<String?>();

  //get access to stream

  Stream<String?> get email => _email.stream.transform(validate_email);
  Stream<String?> get pass => _pass.stream.transform(validate_password);

  //change new data

  Function(String?) get changeEmail => _email.sink.add;
  Function(String?) get changePass => _pass.sink.add;

  dispose(){
    _email.close();
    _pass.close();
  }
}

这里是验证器 class:

class Validators{
  final validate_email = StreamTransformer<String?, String?>.fromHandlers(
    handleData: (String? email, sink){
      if(email!.contains('@')){
        sink.add(email);
      }else{
        sink.addError('Enter valid email');
      }
    }
  );

  final validate_password = StreamTransformer<String?, String?>.fromHandlers(
    handleData: (String? pass, sink){
      if(pass!.length < 4){
        sink.addError('Enter valid password');
      }else{
        sink.add(pass);
      }
    }
  );
}

Answer 1

您需要使用

snapshot.error?.toString()

Answer 2

errorText: snapshot.hasError ? snapshot.error.toString() : "",

这将在将其转换为字符串之前检查是否存在错误。如果没有错误，它也会防止运行时空异常。

Answer 3

有趣的是，没有人知道解决方案，因为他们没有遇到过这个问题。

您只需删除 InputDecoration() 之前的 const 关键字，

下面的代码将无法运行，因为它有 const 关键字 -

TextFormField(
    decoration: const InputDecoration(
                labelText: 'Email', errorText: snapshot.error),

    keyboardType: TextInputType.emailAddress,
         onChanged: bloc.changeEmail,
 );

但是这段代码可以工作，因为它没有 const 关键字 -

TextFormField(
        decoration: InputDecoration(
                    labelText: 'Email', errorText: snapshot.error),
    
        keyboardType: TextInputType.emailAddress,
             onChanged: bloc.changeEmail,
     );

ERROR: The argument type 'Object?' can't be assigned to the parameter type 'String?'

ERROR: The argument type 'Object?' can't be assigned to the parameter type 'String?'

dart

flutter

flutter-streambuilder