flutter 動手擼一個城市選擇citypicker功能

import 'dart:convert';
import 'package:city_picker/city_result.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

typedef ResultBlock = void Function(CityResult result);

class CityPickerView extends StatefulWidget {
  // json數據可以從外部傳入，如果外部有值，取外部值
  final List params;
  // 結果返回
  final ResultBlock onResult;
  CityPickerView({this.onResult, this.params});
  @override
  _CityPickerViewState createState() => _CityPickerViewState();
}

class _CityPickerViewState extends State<CityPickerView> {
  List datas = [];
  int provinceIndex;
  int cityIndex;
  int areaIndex;

  FixedExtentScrollController provinceScrollController;
  FixedExtentScrollController cityScrollController;
  FixedExtentScrollController areaScrollController;

  CityResult result = CityResult();

  bool isShow = false;

  List get provinces {
    if (datas.length > 0) {
      if (provinceIndex == null) {
        provinceIndex = 0;
        result.province = provinces[provinceIndex]['label'];
        result.provinceCode = provinces[provinceIndex]['value'].toString();
      }
      return datas;
    }
    return [];
  }

  List get citys {
    if (provinces.length > 0) {
      return provinces[provinceIndex]['children'] ?? [];
    }
    return [];
  }

  List get areas {
    if (citys.length > 0) {
      if (cityIndex == null) {
        cityIndex = 0;
        result.city = citys[cityIndex]['label'];
        result.cityCode = citys[cityIndex]['value'].toString();
      }
      List list = citys[cityIndex]['children'] ?? [];
      if (list.length > 0) {
        if (areaIndex == null) {
          areaIndex = 0;
          result.area = list[areaIndex]['label'];
          result.areaCode = list[areaIndex]['value'].toString();
        }
      }
      return list;
    }
    return [];
  }

  // 保存選擇結果
  _saveInfoData() {
    var prs = provinces;
    var cts = citys;
    var ars = areas;
    if (provinceIndex != null && prs.length > 0) {
      result.province = prs[provinceIndex]['label'];
      result.provinceCode = prs[provinceIndex]['value'].toString();
    } else {
      result.province = '';
      result.provinceCode = '';
    }

    if (cityIndex != null && cts.length > 0) {
      result.city = cts[cityIndex]['label'];
      result.cityCode = cts[cityIndex]['value'].toString();
    } else {
      result.city = '';
      result.cityCode = '';
    }

    if (areaIndex != null && ars.length > 0) {
      result.area = ars[areaIndex]['label'];
      result.areaCode = ars[areaIndex]['value'].toString();
    } else {
      result.area = '';
      result.areaCode = '';
    }
  }

  @override
  void dispose() {
    provinceScrollController.dispose();
    cityScrollController.dispose();
    areaScrollController.dispose();
    super.dispose();
  }

  @override
  void initState() {
    super.initState();

    //初始化控制器
    provinceScrollController = FixedExtentScrollController();
    cityScrollController = FixedExtentScrollController();
    areaScrollController = FixedExtentScrollController();

    //讀取city.json數據
    if (widget.params == null) {
      _loadCitys().then((value) {
        setState(() {
          isShow = true;
        });
      });
    } else {
      datas = widget.params;
      setState(() {
         isShow = true;
      });
    }
  }

  Future _loadCitys() async {
    var cityStr = await rootBundle.loadString('assets/city.json');
    datas = json.decode(cityStr) as List;
    //result默認取第一組值
    return Future.value(true);
  }

  @override
  Widget build(BuildContext context) {
    return Material(
      child: Container(
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            _firstView(),
            _contentView(),
          ],
        ),
      ),
    );
  }

  Widget _firstView() {
    return Container(
      height: 44,
      child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: <Widget>[
            FlatButton(
              child: Text('取消'),
              onPressed: () {
                Navigator.pop(context);
              },
            ),
            FlatButton(
              child: Text('確定'),
              onPressed: () {
                if (widget.onResult != null) {
                  widget.onResult(result);
                }
                Navigator.pop(context);
              },
            ),
          ]),
      decoration: BoxDecoration(
        border: Border(
            bottom: BorderSide(color: Colors.grey.withOpacity(0.1), width: 1)),
      ),
    );
  }

  Widget _contentView() {
    return Container(
      // color: Colors.orange,
      height: 200,
      child: isShow
          ? Row(
              children: <Widget>[
                Expanded(child: _provincePickerView()),
                Expanded(child: _cityPickerView()),
                Expanded(child: _areaPickerView()),
              ],
            )
          : Center(
              child: CupertinoActivityIndicator(
                animating: true,
              ),
            ),
    );
  }

  Widget _provincePickerView() {
    return Container(
      child: CupertinoPicker(
        scrollController: provinceScrollController,
        children: provinces.map((item) {
          return Center(
            child: Text(
              item['label'],
              style: TextStyle(color: Colors.black87, fontSize: 16),
              maxLines: 1,
            ),
          );
        }).toList(),
        onSelectedItemChanged: (index) {
          provinceIndex = index;
          if (cityIndex != null) {
            cityIndex = 0;
            if (cityScrollController.positions.length > 0) {
              cityScrollController.jumpTo(0);
            }
          }
          if (areaIndex != null) {
            areaIndex = 0;
            if (areaScrollController.positions.length > 0) {
              areaScrollController.jumpTo(0);
            }
          }
          _saveInfoData();
          setState(() {});
        },
        itemExtent: 36,
      ),
    );
  }

  Widget _cityPickerView() {
    return Container(
      child: citys.length == 0
          ? Container()
          : CupertinoPicker(
              scrollController: cityScrollController,
              children: citys.map((item) {
                return Center(
                  child: Text(
                    item['label'],
                    style: TextStyle(color: Colors.black87, fontSize: 16),
                    maxLines: 1,
                  ),
                );
              }).toList(),
              onSelectedItemChanged: (index) {
                cityIndex = index;
                if (areaIndex != null) {
                  areaIndex = 0;
                  if (areaScrollController.positions.length > 0) {
                    areaScrollController.jumpTo(0);
                  }
                }
                _saveInfoData();
                setState(() {});
              },
              itemExtent: 36,
            ),
    );
  }

  Widget _areaPickerView() {
    return Container(
      width: double.infinity,
      child: areas.length == 0
          ? Container()
          : CupertinoPicker(
              scrollController: areaScrollController,
              children: areas.map((item) {
                return Center(
                  child: Text(
                    item['label'],
                    style: TextStyle(color: Colors.black87, fontSize: 16),
                    maxLines: 1,
                  ),
                );
              }).toList(),
              onSelectedItemChanged: (index) {
                areaIndex = index;
                _saveInfoData();
                setState(() {});
              },
              itemExtent: 36,
            ),
    );
  }
}

class CityResult {
  /// 省市區
  String province = '';
  String city = '';
  String area = '';

  /// 對應的編碼
  String provinceCode = '';
  String cityCode = '';
  String areaCode = '';

  CityResult({
    this.province,
    this.city,
    this.area,
    this.provinceCode,
    this.cityCode,
    this.areaCode,
  });

  CityResult.fromJson(Map<String, dynamic> json) {
    province = json['province'];
    city = json['city'];
    area = json['area'];
    provinceCode = json['provinceCode'];
    cityCode = json['cityCode'];
    areaCode = json['areaCode'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> datas = new Map<String, dynamic>();
    datas['province'] = this.province;
    datas['city'] = this.city;
    datas['area'] = this.area;
    datas['provinceCode'] = this.provinceCode;
    datas['cityCode'] = this.cityCode;
    datas['areaCode'] = this.areaCode;

    return datas;
  }
}

 // var cityStr = await rootBundle.loadString('assets/city.json');
    // List datas = json.decode(cityStr) as List;
  showModalBottomSheet(
      context: context,
      isScrollControlled: true,
      builder: (ctx) {
        return CityPickerView(
          // params: datas,
          onResult: (res) {
            print(res.toJson());
            setState(() {
              citySelect = res.toJson().toString();
            });
          },
        );
      },
    );