程式碼：

uitls下的city.js為資料來源JS 直接引入

      switchcity.js

var city = require('../../utils/city.js');


Page({
  data: {
    searchLetter: [],
    showLetter: "",
    winHeight: 0,
    tHeight:0,
    bHeight:0,
    startPageY:0,
    cityList:[],
    isShowLetter:false,
    scrollTop:0,
    city:""
  },
  onLoad: function (options) {
    // 生命週期函式--監聽頁面載入
    var searchLetter = city.searchLetter;
    var cityList=city.cityList();
    // console.log(cityInfo);

    var sysInfo = wx.getSystemInfoSync();
    console.log(sysInfo);
    var winHeight = sysInfo.windowHeight;

    //新增要匹配的字母範圍值
    //1、更加螢幕高度設定子元素的高度
    var itemH = winHeight / searchLetter.length;
    var tempObj = [];
    for (var i = 0; i < searchLetter.length; i++) {
      var temp = {};
      temp.name = searchLetter[i];
      temp.tHeight = i * itemH;
      temp.bHeight = (i + 1) * itemH;

      tempObj.push(temp)
    }
    
    this.setData({
      winHeight: winHeight,
      itemH: itemH,
      searchLetter: tempObj,
      cityList:cityList
    })

    console.log(this.data.cityInfo);
  },
  onReady: function () {
    // 生命週期函式--監聽頁面初次渲染完成

  },
  onShow: function () {
    // 生命週期函式--監聽頁面顯示

  },
  onHide: function () {
    // 生命週期函式--監聽頁面隱藏

  },
  onUnload: function () {
    // 生命週期函式--監聽頁面解除安裝

  },
  onPullDownRefresh: function () {
    // 頁面相關事件處理函式--監聽使用者下拉動作

  },
  onReachBottom: function () {
    // 頁面上拉觸底事件的處理函式

  },
  onShareAppMessage: function () {
    // 使用者點選右上角分享
    return {
      title: 'title', // 分享標題
      desc: 'desc', // 分享描述
      path: 'path' // 分享路徑
    }
  },
  searchStart: function (e) {
    var showLetter = e.currentTarget.dataset.letter;
    var pageY = e.touches[0].pageY;
    this.setScrollTop(this,showLetter);
    this.nowLetter(pageY,this);
      this.setData({
        showLetter: showLetter,
        startPageY: pageY,
        isShowLetter:true,
      })
  },
  searchMove: function (e) {
    var pageY = e.touches[0].pageY;
    var startPageY=this.data.startPageY;
    var tHeight=this.data.tHeight;
    var bHeight=this.data.bHeight;
    var showLetter = 0;
    console.log(pageY);
    if(startPageY-pageY>0){ //向上移動
        if(pageY<tHeight){
          // showLetter=this.mateLetter(pageY,this);
          this.nowLetter(pageY,this);
        }
    }else{//向下移動
        if(pageY>bHeight){
            // showLetter=this.mateLetter(pageY,this);
            this.nowLetter(pageY,this);
        }
    }
  },
  searchEnd: function (e) {
    // console.log(e);
    // var showLetter=e.currentTarget.dataset.letter;
    var that=this;
    setTimeout(function(){
      that.setData({
      isShowLetter:false
    })
    },1000)
    
  },
  nowLetter: function (pageY, that) {//當前選中的資訊
    var letterData = this.data.searchLetter;
    var bHeight = 0;
    var tHeight = 0;
    var showLetter="";
    for (var i = 0; i < letterData.length; i++) {
      if (letterData[i].tHeight <= pageY && pageY<= letterData[i].bHeight) {
        bHeight = letterData[i].bHeight; 
        tHeight = letterData[i].tHeight;
        showLetter = letterData[i].name;
        break;
      }
    }

    this.setScrollTop(that,showLetter);

    that.setData({
      bHeight:bHeight,
      tHeight:tHeight,
      showLetter:showLetter,
      startPageY:pageY
      })
  },
  bindScroll:function(e){
    console.log(e.detail)
  },
  setScrollTop:function(that,showLetter){
      var scrollTop=0;
      var cityList=that.data.cityList;
      var cityCount=0;
      var initialCount=0;
      for(var i=0;i<cityList.length;i++){
         if(showLetter==cityList[i].initial){
           scrollTop=initialCount*30+cityCount*41;
            break;
         }else{
            initialCount++;
            cityCount+=cityList[i].cityInfo.length;
         }
      }

      that.setData({
        scrollTop:scrollTop
      })
  },
  bindCity:function(e){
    var city=e.currentTarget.dataset.city;
    this.setData({city:city})
  }
})

switchcity.wxml

<view class="searchLetter touchClass">
    <view wx:for="{{searchLetter}}" style="height:{{itemH}}px" wx:key="index" data-letter="{{item.name}}" catchtouchstart="searchStart" catchtouchmove="searchMove" catchtouchend="searchEnd">{{item.name}}</view>
</view>

<block wx:if="{{isShowLetter}}">
<view class="showSlectedLetter">
    {{showLetter}}
</view>
</block>
<view>當前選擇城市：{{city}}</view>
<scroll-view scroll-y="true" style="height:{{winHeight}}px" bindscroll="bindScroll" scroll-top="{{scrollTop}}">
    <view class="selection" wx:for="{{cityList}}" wx:key="{{item.initial}}">
        <view class="item_letter">{{item.initial}}</view>
        <view class="item_city" wx:for="{{item.cityInfo}}" wx:for-item="ct" wx:key="{{ct.id}}" data-city="{{ct.city}}" bindtap="bindCity">
              {{ct.city}}  
        </view>
    </view>
</scroll-view>
 

css:

.searchLetter{
    position: fixed;
    right: 0;
    width: 40px;
    height: 100%;
    text-align: center;
    justify-content: center;
    display: flex;
    flex-direction: column;
    color: #666;
    z-index: 1
}
.searchLetter view{
    height: 70rpx;
}
.touchClass{
    background-color: rgba(0, 0, 0,0.5);
    color: #fff;
}
.showSlectedLetter{
    background-color: rgba(0, 0, 0,0.5);
    color: #fff;
    display: flex;
    justify-content: center;
    align-items: center;
    position: fixed;
    top:50%;
    left: 50%;
    margin: -50px;
    width: 100px;
    height: 100px;
    border-radius:10px; 
    font-size: 26px;
    z-index: 1
}
.selection{
    display: flex;
    width: 100%;
    flex-direction: column;
}
.item_letter{
    display: flex;
    background-color: #f8f8f8;
    height: 30px;
    padding-left: 10px;
    align-items: center;
}
.item_city{
    display: flex;
    background-color: #fff;
    height: 40px;
    padding-left: 10px;
    align-items: center;
    border-bottom: 1px solid #f8f8f8
}
 

歡迎各位交流批評