flutter 自定义城市选择器

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因为城市选择的数据是从服务器上拿的的，在pub上面也没有找到合适插件，索性就自己写了一个,在写的过程也遇到很多问题，其实就是三个 CupertinoPicker 组合在一起的，当时写的过程中发现 CupertinoPicker setState不更新以及onSelectedItemChanged 调用的问题
CupertinoPicker 不更新可以通过 GlobalKey 来解决 onSelectedItemChanged 调用问题可以通过 NotificationListener监听来拿到当前的索引

这里分享一下实现代码

import 'dart:async';

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:zhengda_health/app/custom_widgets/custom_text.dart';
import 'package:zhengda_health/app/http_util/http_api.dart';
import 'package:zhengda_health/app/http_util/http_util.dart';
import 'package:zhengda_health/app/support/app_color.dart';

//省市区类型
enum CityType {
  province,
  city,
  area
}

class CityAlertView extends StatefulWidget {

  CityAlertViewDelegate delegate;
  CityAlertView({Key key,this.delegate}) : super(key: key);

  @override
  _CityAlertViewState createState() => _CityAlertViewState();
}

class _CityAlertViewState extends State<CityAlertView> {

  List <CityAlertModel> _provinceList = [];

  List <CityAlertModel> _cityList = [];

  List <CityAlertModel> _areaList = [];

  GlobalKey _provinceGlobalKey = GlobalKey();

  GlobalKey _cityGlobalKey = GlobalKey();

  GlobalKey _areaGlobalKey = GlobalKey();

  int _provinceIndex = 0;

  int _cityIndex = 0;

  int _areaIndex = 0;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();


    _getAreaData(cityType:CityType.province,pid: '0' ,onSuccess: (){
      _getAreaData(cityType: CityType.city,pid: _provinceList.first.adcode,onSuccess: (){
          _getAreaData(cityType:  CityType.area,pid: _cityList.first.adcode,onSuccess: (){

          });
      });
    });

  }

  void _getAreaData({CityType cityType,String pid,Function onSuccess}){
    HttpUtil.getHttp('${HttpApi.areaInfo}?pid=$pid',onSuccess: (res){
      List<CityAlertModel> list =List<CityAlertModel>.from(res['areaLists'].map((it) => CityAlertModel.fromJson(it)));

      if(cityType == CityType.province){
        _provinceGlobalKey  =GlobalKey();;
        _provinceList = list ;

      }else if(cityType == CityType.city){

        _cityGlobalKey  =GlobalKey();;
        _cityList =list;
      }else{
        _areaGlobalKey  =GlobalKey();;
        _areaList = list;
      }
      setState(() {});
      onSuccess();

    });
  }

  //确定生成回调
  void _confirmClick(BuildContext context ){
    if(widget.delegate != null){
      widget.delegate.confirmClick([_provinceList[_provinceIndex],_cityList[_cityIndex],_areaList[_areaIndex]]);
    }
    Navigator.of(context).pop();

  }

  //取消
  void _canlClick(BuildContext context){
    Navigator.of(context).pop();
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(child: Column(
      mainAxisSize: MainAxisSize.min,
      children: [
        SizedBox(height: 8,),
        _headerWidget(context),
        Row(
          children: [

            _pickerViewWidget(models:_provinceList,
                key:_provinceGlobalKey ,
                onSelectedItemChanged: (v){
              _provinceIndex = v;
              _getAreaData(cityType: CityType.city,pid: _provinceList[v].adcode,onSuccess: (){
                _getAreaData(cityType: CityType.area,pid: _cityList.first.adcode,onSuccess: (){
                });
              });

            }),

            _pickerViewWidget(models: _cityList,key:_cityGlobalKey,onSelectedItemChanged: (v){
              _cityIndex = v;
              _getAreaData(cityType: CityType.area,pid: _cityList[v].adcode,onSuccess: (){});
            } ),

            _pickerViewWidget(models: _areaList,key:_areaGlobalKey,onSelectedItemChanged: (v){
              _areaIndex =v;
            } ),
          ],
        )
      ],
    ));
  }

  Widget _headerWidget(BuildContext context){
    return Row(
      children: [
        _buttonWidget(title: '取消',textColor: Colors.black38,callback: (){
          _canlClick(context);
        }),
        Expanded(child: Container()),
        _buttonWidget(title: '确定',textColor: Colors.black,callback: (){
          _confirmClick(context);
        }),
      ],
    );
  }

  //piceerView
  Widget _pickerViewWidget({List<CityAlertModel> models,Key key,
    ValueChanged<int> onSelectedItemChanged,}){
    return Expanded(
        child: SizedBox(
            height: 200,
            child: NotificationListener(
              onNotification: (Notification scrollNotification) {
                  if (scrollNotification is ScrollEndNotification &&
                      scrollNotification.metrics is FixedExtentMetrics)
                  {
                    print((scrollNotification.metrics as FixedExtentMetrics).itemIndex); // Index of the list
                    onSelectedItemChanged((scrollNotification.metrics as FixedExtentMetrics).itemIndex);

                    return true;
                  } else {
                    return false;
                  }
              },
              child: CupertinoPicker(
                  key: key,
                  useMagnifier: true,
                  magnification: 1.2,
                  selectionOverlay: _selectionOverlayWidget(),
                  itemExtent: 34,
                  onSelectedItemChanged: (v){},
                  children: models.map((e) => _itemsWidget(e.name)).toList()),
            ))
    );
  }

  // 中间分割线
  Widget _selectionOverlayWidget(){
    return Padding(
      padding: EdgeInsets.only(left: 0, right: 0),
      child: Column(
        children: [
          Divider(
            height: 1,
            color: AppColor.green86Color,
          ),
          Expanded(child: Container()),
          Divider(
            height: 1,
            color: AppColor.green86Color,
          ),
        ],
      ),
    );
  }

  // cellItems
  Widget _itemsWidget(e){
    return Container(
      alignment: Alignment.center,
      child:  CustomText(e,fontSize: 14,),
    );
  }

  //公共button
  Widget _buttonWidget({String title ,Color textColor ,VoidCallback callback}){
    return  InkWell(
      onTap: callback,
      child: Container(
        alignment: Alignment.center,
        padding:EdgeInsets.only(left: 16,right: 16),
        height: 40,
        child: CustomText(title,color: textColor,),
      ),
    );
  }

}

abstract class  CityAlertViewDelegate{
  void confirmClick(List<CityAlertModel> models){}
}

class CityAlertModel {
  int id;
  String pAdcode;
  String adcode;
  String name;
  String level;
  String pinyin;
  String first;
  String lng;
  String lat;

  CityAlertModel(
      {this.id,
        this.pAdcode,
        this.adcode,
        this.name,
        this.level,
        this.pinyin,
        this.first,
        this.lng,
        this.lat});

  CityAlertModel.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    pAdcode = json['p_adcode'];
    adcode = json['adcode'];
    name = json['name'];
    level = json['level'];
    pinyin = json['pinyin'];
    first = json['first'];
    lng = json['lng'];
    lat = json['lat'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['p_adcode'] = this.pAdcode;
    data['adcode'] = this.adcode;
    data['name'] = this.name;
    data['level'] = this.level;
    data['pinyin'] = this.pinyin;
    data['first'] = this.first;
    data['lng'] = this.lng;
    data['lat'] = this.lat;
    return data;
  }
}

调用

class _AddAddressPageState extends State<AddAddressPage> implements CityAlertViewDelegate 
要implements 实现回调协议
  //回调省市区
  @override
  void confirmClick(List<CityAlertModel> models) {}

//调用弹框
  showModalBottomSheet(
        context: context,
        shape: RoundedRectangleBorder(
            borderRadius: BorderRadiusDirectional.circular(10)),
        builder: (BuildContext context) {
          return CityAlertView(delegate: this,);
        });