Android 未处理的异常：在模型类的setter中设置值时NoSuchMethodError

我正在学习颤振编程。我正在做一个简单的登记表，现在只有两个字段，名字和出生日期。我已经成功地用db创建了一个简单的便笺制作应用程序，因此遵循了这里的相同说明。但遇到未经处理的错误异常：NoSuchMethodError:对null调用了setter“regday=”

注册模型类

设置值的代码

痕迹

---

预期的输出将是一个显示成功消息的警报框，但会抛出此错误。非常感谢您的帮助。

这是因为您的注册表对象为空。在_save函数的第一行中添加

reg = RegistrationModel('','');

试一试

---

您在哪里从_savemethod？RegistrationModel reg；在类RegistrationState extends State classI中，我在代码段中根本看不到它。你能更新一下吗？更新了。请看。好的，您定义了如下RegistrationModel reg；但为了调用该变量的任何方法/属性，必须对其进行初始化。在本例中，必须调用已定义的构造函数，如reg=RegistrationModel，；。或者您可以将coConstructor的参数更改为可选，然后调用reg=RegistrationModel；。这在功能上与去年发布的有什么不同吗？

class Registration extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return RegistrationState();
  }
}

class RegistrationState extends State {
  RegistrationModel reg;

  DatabaseHelper databaseHelper = DatabaseHelper();

  var _minimumPadding = 5.0;
  var _formKey;

  TextEditingController _nameController = new TextEditingController();
  TextEditingController _dobController = new TextEditingController();

  @override
  Widget build(BuildContext context) {
    TextStyle textStyle = Theme.of(context).textTheme.title;

//    _nameController.text = reg.name;
//    _dobController.text = reg.dob;

    //DATEPICKER
    DateTime _selectedDate = DateTime.now();

    Future<Null> _selectDate(BuildContext context) async {
      final DateTime picked = await showDatePicker(
          context: context,
          initialDate: _selectedDate,
          firstDate: DateTime(1990),
          lastDate: DateTime(2101));
      if (picked != null && picked != _selectedDate) {
        print("Selected Date in the func : $picked");
        setState(() {
          _selectedDate = picked;
          _dobController.text = (picked.day).toString() +
              "/" +
              (picked.month).toString() +
              "/" +
              (picked.year).toString();
        });
//        Focus.clear(context);

      }
    }

    return Scaffold(
      appBar: AppBar(
        title: Text("Register"),
      ),
      body: Form(
        key: _formKey,
        child: Padding(
          padding: EdgeInsets.only(
            top: _minimumPadding * 2,
            left: _minimumPadding * 2,
            right: _minimumPadding * 2,
          ),
          child: ListView(
            children: <Widget>[
              //NAME
              TextField(
                controller: _nameController,
                style: textStyle,
                onChanged: (value) {
                  updateName();
                },
                decoration: InputDecoration(
                  labelStyle: textStyle,
                  labelText: "Name",
                  icon: Icon(Icons.person),
                ),
              ),

              //DATE OF BIRTH
              TextField(
                controller: _dobController,
                keyboardType: TextInputType.datetime,
                onChanged: (value) {
                  updateDob();
                },
                decoration: InputDecoration(
                  labelStyle: textStyle,
                  labelText: "Date Of Birth",
                  icon: Icon(Icons.calendar_today),
                ),
                onTap: () {
                  _selectDate(context);
                },
              ),

              RaisedButton(
                child: Text(
                  "Register",
                  textScaleFactor: 1.5,
                ),
                color: Theme.of(context).primaryColor,
                textColor: Theme.of(context).primaryColorLight,
                onPressed: () {
                  _save();
                  print("Save button pressed");
                },
              ),
            ],
          ),
        ),
      ),
    );
  }

void _save() async {

    String today = DateFormat.yMMMd().format(DateTime.now());
    print("Today : $today");
    reg.regday = today;
    reg.name = _nameController.text;
    reg.dob = _dobController.text;

    int result;
    if (reg.id != null) //UPDATE
    {
      result = await databaseHelper.updateRegister(reg);
    } else {
      result = await databaseHelper.inserRegister(reg);
    }

    if (result != 0) //SUCCESS
    {
      _showAlertDialog("Success", "Registered successfully");
    } else //FAILED
    {
      _showAlertDialog("Failed", "Problem in registering");
    }
  }

[ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The setter 'regday=' was called on null.
E/flutter (21661): Receiver: null
E/flutter (21661): Tried calling: regday="Apr 1, 2019"
E/flutter (21661): #0      Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:50:5)
E/flutter (21661): #1      RegistrationState._save (package:registration_test/screens/registration_screen.dart:136:9)
E/flutter (21661): <asynchronous suspension>
E/flutter (21661): #2      RegistrationState.build.<anonymous closure> (package:registration_test/screens/registration_screen.dart:111:19)
E/flutter (21661): #3      _InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:513:14)
E/flutter (21661): #4      _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:568:30)
E/flutter (21661): #5      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:120:24)
E/flutter (21661): #6      TapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:242:9)
E/flutter (21661): #7      TapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:204:7)
E/flutter (21661): #8      GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:156:27)
E/flutter (21661): #9      _WidgetsFlutterBinding&BindingBase&GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:218:20)
E/flutter (21661): #10     _WidgetsFlutterBinding&BindingBase&GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:192:22)
E/flutter (21661): #11     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:149:7)
E/flutter (21661): #12     _WidgetsFlutterBinding&BindingBase&GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:101:7)
E/flutter (21661): #13     _WidgetsFlutterBinding&BindingBase&GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:85:7)
E/flutter (21661): #14     _rootRunUnary (dart:async/zone.dart:1136:13)
E/flutter (21661): #15     _CustomZone.runUnary (dart:async/zone.dart:1029:19)
E/flutter (21661): #16     _CustomZone.runUnaryGuarded (dart:async/zone.dart:931:7)
E/flutter (21661): #17     _invoke1 (dart:ui/hooks.dart:223:10)
E/flutter (21661): #18     _dispatchPointerDataPacket (dart:ui/hooks.dart:144:5)

reg = RegistrationModel('','');

RegistrationModel reg = RegistrationModel();