使用 Getx ，来自 firestore 的 Flutter Dropdown 提要，选定的值在选择新值时不会改变，

编程问答 2022-05-29

问题描述

模型：为类别制作此模型。

import 'package:cloud_firestore/cloud_firestore.dart';

class CatagoryModel {

String id;
  String catagoryname;
  Timestamp date;
  bool status;
  String user;

  CatagoryModel(this.id,this.catagoryname,this.date,this.user,this.status);

  CatagoryModel.fromDocumentSnapshot(DocumentSnapshot documentSnapshot) {
    id = documentSnapshot.id;
    catagoryname = documentSnapshot.data()['catagoryname'];
    date = documentSnapshot.data()['date'];
    user = documentSnapshot.data()['user'];
    status = documentSnapshot.data()['status'];
  }
}

Service：此代码处理模型和 Firestore 数据并将其传递给 Getx 控制器。

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:get/get.dart';
import 'package:talhatraders/app/data/catagorymodel.dart';

class Database {
  final FirebaseFirestore _firebase = FirebaseFirestore.instance;

  Future<void> catagoryAdd(String catagoryname,bool status) async {
    try {
      await _firebase.collection('catagorydb').add({
        'date': Timestamp.now(),'status': status,'catagoryname': catagoryname,'user':'user1'
      });
    } catch (e) {
      print(e);
    }
  }

  Future<void> catagoryStatus(CatagoryModel catagorymodel)async{

    try {
      await _firebase.collection('catagorydb').doc(catagorymodel.id).update({'status':!catagorymodel.status});
      
    } catch (e) {
    print(e);
    }

  }

  Future<void> catagoryDelete(CatagoryModel catagorymodel)async{

    try {

      await _firebase.collection('catagorydb').doc(catagorymodel.id).delete();
      
    } catch (e) {
    }
  }

  Stream<List<CatagoryModel>> catagoryStream() {
    return _firebase
        .collection('catagorydb')
        .snapshots()
        .map((QuerySnapshot querysnapshot) {
      List<CatagoryModel> todoData= List();
      querysnapshot.docs.forEach((element) {
        todoData.add(CatagoryModel.fromDocumentSnapshot(element));
      });

      return todoData;
    });
  }
}

Getx 控制器：这里我使用了 obs 字符串，该字符串在从 dropbox 中选择新值时发生变化

import 'package:flutter/material.dart';
import 'package:get/get.dart';
import 'package:talhatraders/app/data/catagorymodel.dart';
import 'package:talhatraders/app/modules/catagory/controllers/catagoryservice.dart';

class ProductentryController extends GetxController {
  Rx<List<CatagoryModel>> catagoryList = Rx<List<CatagoryModel>>();

  List<CatagoryModel> get catagories => catagoryList.value;

  var selectedItem = "Select Catagory..".obs;
  void changeSelect(String select) {
    selectedItem.value = select;
    
  }


  @override
  void onInit() {
    catagoryList.bindStream(Database().catagoryStream());
  }
}

GetxViewPaege：在 ViewPage UI 中工作正常，但从下拉列表中选择新值时值没有改变

import 'package:cloud_firestore/cloud_firestore.dart';

import 'package:flutter/material.dart';


import 'package:get/get.dart';
import 'package:flutter/services.dart';

import 'package:talhatraders/app/data/catagorymodel.dart';
import 'package:talhatraders/app/modules/catagory/controllers/catagory_controller.dart';

import 'package:talhatraders/app/modules/productentry/controllers/productentry_controller.dart';



class ProductentryView extends GetView<ProductentryController> {
  ProductentryController productController = Get.put(ProductentryController());




  final FirebaseFirestore _firebase = FirebaseFirestore.instance;
  //Color currentColor =Colors.limeAccent;

 

  String catagory;
  

 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('New Item'),actions: [],),body: Column(children: [
        GetX<ProductentryController>(
          init: Get.put<ProductentryController>(ProductentryController()),builder: (ProductentryController productentryController) {
            return Expanded(
              child: Container(
                child: Padding(
                  padding: const EdgeInsets.only(
                      bottom: 12,top:40,left: 10.0,right: 15.0),child: InputDecorator(
                      decoration: InputDecoration(
                        fillColor: Colors.transparent,hintStyle: Theme.of(context).textTheme.bodyText2,border: OutlineInputBorder(
                          borderRadius: BorderRadius.circular(15),borderSide: BorderSide(
                            width: 10,style: BorderStyle.none,filled: true,contentPadding: EdgeInsets.all(16),child: DropdownButtonHideUnderline(
                        child: DropdownButton(
                            isExpanded: true,isDense:
                                true,// Reduces the dropdowns height by +/- 50%
                            icon: Icon(Icons.keyboard_arrow_down),hint: Text(
                                '${productentryController.selectedItem.toString()}'),value: catagory,items: productentryController.catagories
                                .map((CatagoryModel item) {
                              return DropdownMenuItem(
                                value: item.catagoryname,child: Text(item.catagoryname),);
                            }).toList(),onChanged: (selectedItem) {



                               productentryController.changeSelect(Item);

                              catagory=productController.selectedItem.value;
                            }),)),);
          },]),);
  }
}

解决方法

像这样创建一个下拉选择器类并在你想要的地方使用它

class DropdownPickerGetX extends StatelessWidget {
  DropdownPickerGetX(
      {this.menuOptions,this.selectedOption,this.onChanged});

  final List<dynamic> menuOptions;
  final String selectedOption;
  final void Function(String) onChanged;

  @override
  Widget build(BuildContext context) {
    //if (Platform.isIOS) {}
    return DropdownButton<String>(
        items: menuOptions
            .map((data) => DropdownMenuItem<String>(
                  child: Row(
                    mainAxisAlignment: MainAxisAlignment.start,children: <Widget>[
                      Icon(data.icon),SizedBox(width: 10),Text(
                        data.value,),],value: data.key,))
            .toList(),value: selectedOption,onChanged: onChanged);
  }
}
,

这就是我在下拉菜单中使用 GetX 的方式

我正在使用具有 MVC 结构的 GetX、用于列表或响应等的模型、用于在 UI 中显示数据的视图、用于处理业务逻辑的控制器。首先查看我在此示例中使用的示例响应。

响应

{
  "users": [
    {
      "user_type_id": "0","user_type": "USER 1"
    },{
      "user_type_id": "1","user_type": "USER 2"
    },{
      "user_type_id": "2","user_type": "USER 3"
    },{
      "user_type_id": "3","user_type": "USER 4"
    }
  ]
}

现在，在您的模型类中。比方说 -> dropdown_model.dart

这是您列表的模型，它将显示在下拉列表中。您可以在 quicktype.io

为您的回复创建模型 
import 'dart:convert';

DropdownModel dropdownModelFromJson(String str) => DropdownModel.fromJson(json.decode(str));

String dropdownModelToJson(DropdownModel data) => json.encode(data.toJson());

class DropdownModel {
  DropdownModel({
    this.users,});

  List<User> users;

  factory DropdownModel.fromJson(Map<String,dynamic> json) => DropdownModel(
    users: List<User>.from(json["users"].map((x) => User.fromJson(x))),);

  Map<String,dynamic> toJson() => {
    "users": List<dynamic>.from(users.map((x) => x.toJson())),};
}

class User {
  User({
    this.userTypeId,this.userType,});

  String userTypeId;
  String userType;

  factory User.fromJson(Map<String,dynamic> json) => User(
    userTypeId: json["user_type_id"],userType: json["user_type"],dynamic> toJson() => {
    "user_type_id": userTypeId,"user_type": userType,};
}

现在，在您的控制器类中。比方说 -> register_controller.dart

//Make sure to import required packages
class RegisterController extends GetxController{

  //Declaration and initializations
  DropdownModel model;
  Rx<List<User>> userTypeListM = Rx<List<User>>();
  Rx<User>selectedUserType = Rx<User>();
  Rx<String>userTypeId = Rx<String>();
  
  //this is used,just to avoid any null error until list is fetched
  var toggle = false.obs;

  //This is a sample api call,fetch your data/list and assign list to RxList,//Your API Call goes right in this method
  getList() async {
    String data = await rootBundle.loadString('assets/user_type.json');
    model = dropdownModelFromJson(data);
    //if in case userTypeListM.value doesn't work then try userTypeListM.assignAll(model.users) 
    userTypeListM.value = model.users;
    toggle.value = true;
  }

//Call getList() in onInit() method
@override
  void onInit() {
    // TODO: implement onInit
    super.onInit();
    getList();
  }


onSelectionChange(User value){
    
    selectedUserType.value = value;
    userTypeId.value = value.userTypeId;
   
  }

}

现在，在您的 View 类中。比方说 -> register_view.dart

//Make sure to import required packages
class RegisterPage extends StatelessWidget{

final registerController = Get.put(RegisterController());

@override
  Widget build(BuildContext context) {
    return Scaffold(
       body:Center(
         child:Row(
             children:[
                Expanded(
                   flex:1,child: Container(
                      //color: Colors.white,margin: EdgeInsets.only(left: 15,right: 15,top: 16,bottom: 0),padding: EdgeInsets.symmetric(vertical: 5,horizontal: 8),decoration: BoxDecoration(
                         borderRadius: BorderRadius.circular(30),color: Colors.white,boxShadow: [
                            BoxShadow(
                               color: CupertinoColors.lightBackgroundGray,spreadRadius: 5,blurRadius: 25,offset: Offset(5,5),]
                      ),child: Column(
                         /* crossAxisAlignment: CrossAxisAlignment.center,mainAxisAlignment: MainAxisAlignment.center,*/
                         children: <Widget>[
                            Obx(()=> registerController.toggle.value
                                 ? DropdownButton(
                                      value: registerController.selectedUserType!=null ? registerController.selectedUserType.value: null,items: registerController.userTypeListM.value
                                      .map<DropdownMenuItem<User>>((User value) {
                                      return DropdownMenuItem<User>(
                                        value: value,child: Text(value.userType.toString()),);
                                    }).toList(),onChanged: (User value){
                                      registerController.selectedUserType.value = value;
                                      registerController.userTypeId.value = value.userTypeId;
                                      
                                      registerController.update();
                                    },underline: Container(color: Colors.transparent,hint: Text("Select value from dropdown"),isExpanded: true,)
                                      : Container()
                                  )
                                ],)
                          ),]
                 ),)
        );
    }
}

就是这样！。它应该适用于下拉列表中的任何自定义模型。

androidandroiddropdowngetx

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