Detailed explanation of city selector city switching in WeChat applet development

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) {
  // 生命周期函数--监听页面加载
  var searchLetter = city.searchLetter;
  var cityList = city.cityList();
  // console.log(cityInfo);

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

  //添加要匹配的字母范围值
  //1、更加屏幕高度设置子元素的高度
  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 () {
  // 生命周期函数--监听页面初次渲染完成

 },
 onShow: function () {
  // 生命周期函数--监听页面显示

 },
 onHide: function () {
  // 生命周期函数--监听页面隐藏

 },
 onUnload: function () {
  // 生命周期函数--监听页面卸载

 },
 onPullDownRefresh: function () {
  // 页面相关事件处理函数--监听用户下拉动作

 },
 onReachBottom: function () {
  // 页面上拉触底事件的处理函数

 },
 onShareAppMessage: function () {
  // 用户点击右上角分享
  return {
   title: &#39;title&#39;, // 分享标题
   desc: &#39;desc&#39;, // 分享描述
   path: &#39;path&#39; // 分享路径
  }
 },
 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) { //向上移动
   if (pageY < tHeight) {
    // showLetter=this.mateLetter(pageY,this);
    this.nowLetter(pageY, this);
   }
  } else {//向下移动
   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) {//当前选中的信息
  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 })
 }
})