android - 未处理的异常 : NoSuchMethodError while setting values in setter in Model class

Question

我正在学习 Flutter 编程。我正在制作一个简单的注册表，目前只有 2 个字段，姓名和出生日期。我已经使用 db 成功创建了一个简单的笔记制作应用程序，因此请按照此处的相同说明进行操作。但是遇到错误“未处理的异常:NoSuchMethodError:setter 'regday=' was called on null。”

注册模型类

class RegistrationModel
{
  int _id;
  String _name;
  String _dob;
  String _regDay;

  RegistrationModel(this._name, this._dob, [this._regDay]);

  RegistrationModel.withId(this._id, this._name, this._dob, [this._regDay]);

  //GETTERS
  int get id => _id;

  String get name => _name;

  String get dob => _dob;

  String get regday => _regDay;

  //SETTER
  set name(String newName)
  {
    if(newName.length <= 30)
      {
        this._name = newName.trim();
      }
  }

  set dob(String newDob)
  {
    this._dob = newDob;
  }

  set regday(String newRegDay)
  {
    print("New Reg Day : $newRegDay");
    this._regDay = newRegDay;
  }

  //CONVERT REG OBJ TO MAP
  Map<String, dynamic> toMap()
  {
    var map = Map<String, dynamic>();

    if(id != null)
      {
        map['id'] = _id;
      }
    map['name'] = _name;
    map['dob'] = _dob;
    map['regday'] = _regDay;

    return map;
  }

  //CONVERT MAP TO REG
  RegistrationModel.fromMapObject(Map<String, dynamic> map){
    this._id = map['id'];
    this._name = map['name'];
    this._dob = map['dob'];
    this._regDay = map['regday'];
  }
}

设置值的代码

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");
    }
  }

痕迹

[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)

预期的输出将是一个显示成功消息的警告框，但会抛出此错误。任何帮助将不胜感激。

Answer 1

那是因为你的 reg 对象是空的。在 _save 函数的第一行添加

reg = RegistrationModel('','');