setter 'firstName=' 被调用为 null。接收者：null 尝试调用：firstName="hfjfhd" in flutter

Question

请有人帮助我，自从过去两天以来，我一直遇到这个错误，我正在尝试使用单击按钮从输入表单发送数据到列表，单击按钮时，表单打开同一页面，但是当我在表单中输入数据并单击提交按钮时，没有任何反应，并且在终端上显示 The setter 'firstName=' was called on null。接收者：null 尝试调用：firstName="hfjfhd".

这是我的 model.dart 文件 class Model { string firstName = ""; String lastName = ""; String email = ""; String password = ""; Model({this.firstName, this.lastName, this.email, this.password});}

这是我打开表格并显示结果的主文件。

import 'package:flutter/material.dart';
import 'model.dart';
import 'package:dummy_project/components/save_data_from_input_into_object/form.dart';
import 'package:dummy_project/components/save_data_from_input_into_object/result.dart';

class DialogForm extends StatefulWidget {
  List<Model> models = <Model>[];
  Model tempModel;

  DialogForm();

  @override
  State<DialogForm> createState() => _ResultState();
  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<Model>('model', tempModel));
  }
}

class _ResultState extends State<DialogForm> {
  final _formKey = GlobalKey<FormState>();

  @override

  
  Widget build(BuildContext context) {
    return (Scaffold(
      appBar: AppBar(title: Text('Successful')),
      
      body: Container(
        margin: EdgeInsets.all(10.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            
            Flexible(
              child: ListView.builder(
                itemCount: widget.models.length,
                itemBuilder: (context, index) {
                  return ListTile(
                    title: Text(widget.models[index].firstName),
                    subtitle: Text(widget.models[index].lastName),
                    trailing: Text(widget.models[index].email),
                  );
                },
              ),
            ),

            Align(
              child: RaisedButton(
                child: Text('Click Me!'),
                  onPressed: (){
                showDialog(
                    context: context,
                    builder: (BuildContext context){
                      return AlertDialog(
                        content: Stack(
                          overflow: Overflow.visible,
                          children: <Widget>[
                            Positioned(
                              right: -40,
                              top: -40,
                              child: InkResponse(
                                onTap: () {
                                  Navigator.of(context).pop();
                                },
                                child: CircleAvatar(
                                  child: Icon(Icons.close),
                                  backgroundColor: Colors.red,
                                ),
                              ),
                            ),
                            Form(
                                key: _formKey,
                                child: Column(
                                  mainAxisSize: MainAxisSize.min,
                                  children: <Widget>[
                                    Padding(
                                      padding: EdgeInsets.all(8.0),
                                      child: MyTextFormField(
                                        hintText: 'First Name',
                                        validator: (String value) {
                                          if (value.isEmpty) {
                                            return 'Enter your first name';
                                          }
                                          return null;
                                        },
                                        onSaved: (String value) {
                                          widget.tempModel.firstName = value;
                                        },
                                      ),
                                    ),
                                    Padding(
                                      padding: EdgeInsets.all(8.0),
                                      child: MyTextFormField(
                                        hintText: 'Last Name',
                                        validator: (String value) {
                                          if (value.isEmpty) {
                                            return 'Enter your last name';
                                          }
                                          return null;
                                        },
                                        onSaved: (String value) {
                                          widget.tempModel.lastName = value;
                                        },
                                      ),
                                    ),
                                    Padding(
                                      padding: EdgeInsets.all(8.0),
                                      child: MyTextFormField(
                                        hintText: 'Enter email',
                                        isEmail: true,
                                        // validator: (String value) {
                                        //   if (!validator.isEmail(value)) {
                                        //     return 'Please enter a valid email';
                                        //   }
                                        //   return null;
                                        // },
                                        onSaved: (String value) {
                                          widget.tempModel.email = value;
                                        },
                                      ),
                                    ),
                                    Padding(
                                      padding: const EdgeInsets.all(8.0),
                                      child: RaisedButton(
                                        child: Text("Submit"),
                                        onPressed: () {
                                          if (_formKey.currentState.validate()) {
                                            _formKey.currentState.save();
                                            widget.models.add(widget.tempModel);
                                            Navigator.push(
                                                context,
                                                MaterialPageRoute(
                                                    builder: (context) => DialogForm()));
                                          }
                                        },
                                      ),
                                    )
                                  ],
                                )
                            ),
                          ],
                        ),
                      );
                    }

                );
              }

              ),
              alignment: Alignment.bottomRight,
            ),
          ],

        ),
      ),
    )
    );
  }
}

class MyTextFormField extends StatelessWidget {
  final String hintText;
  final Function validator;
  final Function onSaved;
  final bool isPassword;
  final bool isEmail;

  MyTextFormField({
    this.hintText,
    this.validator,
    this.onSaved,
    this.isPassword = false,
    this.isEmail = false,
  });

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: EdgeInsets.all(8.0),
      child: TextFormField(
        decoration: InputDecoration(
          hintText: hintText,
          contentPadding: EdgeInsets.all(15.0),
          border: InputBorder.none,
          filled: true,
          fillColor: Colors.grey[200],
        ),
        obscureText: isPassword ? true : false,
        validator: validator,
        onSaved: onSaved,
        keyboardType: isEmail ? TextInputType.emailAddress : TextInputType.text,
      ),
    );
  }
}```

Answer 1

使其可为空：“?”这里声明它可以默认为 null 或通过任何操作。

建议：使用 textEditingController 获取输入值，并传递它。并在显示模型中的文本时使用 null 安全检查，因为您将其定义为 null。

widget.models[index].firstName ?? "First Name"

以上，“？？”意味着如果左语句在任何情况下都是空的，那么右语句将被执行，所以如果你在你的文本字段中得到“名字”然后它从模型中得到空。

class Model{

String? firstName;
String? lastName;
String? email;
String? password;

Model({
 this.firstName,
 this.lastName,
 this.email,
 this.password
});
}

如果您有任何疑问，请告诉我谢谢

Answer 2

您没有初始化 tempModel，因此它将为空，这就是为什么您在 widget.tempModel.firstName.

处收到错误消息的原因

而不是 Model tempModel; 试试：

Model tempModel = Model();

或

final tempModel = Model();

setter 'firstName=' 被调用为 null。接收者：null 尝试调用：firstName="hfjfhd" in flutter

The setter 'firstName=' was called on null. Receiver: null Tried calling: firstName="hfjfhd" in flutter

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