小程序自定义组件实现城市选择功能

<scroll-view class='cityList' scroll-y scroll-into-view='{{currentIndex}}' scroll-top='{{scrollTop}}'>
   <view wx:for='{{allCities}}'>
     <view class='letter-class' id="id{{index}}">{{item.letter}}</view>
     <view class='item-class' wx:for='{{item.cityList}}' wx:for-item='cityItem' bindtap='citySelectEvent' data-city='{{cityItem.name}}' data-letter='{{cityItem.key}}'>{{cityItem.name}}</view>
   </view>
</scroll-view>
 
<view class='citySlide' catchtouchstart='slideStart' catchtouchmove='slideMove' catchtouchend='slideEnd'>
   <view class='citySlideItem' wx:for='{{allCities}}' data-index='{{index}}'>{{item.letter}}</view>
</view>
 
<text class='letterText' hidden='{{isLetterHidden}}' style='top:{{letterTop}}px;left:{{letterLeft}}px'>{{letterText}}</text>

<scroll-view class='cityList' scroll-y scroll-into-view='{{currentIndex}}' scroll-top='{{scrollTop}}'>
  .
  .
  .
//id不能以数字开头
<view class='letter-class' id="id{{index}}">{{item.letter}}</view>

/**
   * 组件的初始数据
   */
   data: {
     currentIndex: 'id0'
   }

.citySlide {
   display: flex;
   flex-direction: column;
   width: 60rpx;
   height: calc(100% - 80px);
   position: absolute;
   top: 40px;
   right: 16rpx;
   align-items: center;
   justify-content: center;
   background-color: #ccc;
   opacity: 0.6;
}

 wx.getSystemInfo({
        success: function (res) {
          letterLineHeight = (res.windowHeight - 80) / that.data.allCities.length;
          that.setData({
             letterTop: res.windowHeight / 2 - 30,
             letterLeft: res.windowWidth / 2 - 30
          });
        }
     })

slideStart: function (e) {
  //手指触摸的y坐标值
  var touchY = e.touches[0].clientY;
  //布局距离屏幕顶端距离
  var offsetTop = e.currentTarget.offsetTop;
  var index = parseInt((touchY - offsetTop) / letterLineHeight);
  this.setData({
    currentIndex: 'id' + index,
    isLetterHidden: false,
    letterText: this.data.allCities[index].letter
  });
},
 
slideMove: function (e) {
  var touchY = e.touches[0].clientY;
  var offsetTop = e.currentTarget.offsetTop;
  var index = parseInt((touchY - offsetTop) / letterLineHeight);
  this.setData({
    currentIndex: 'id' + index,
    isLetterHidden: false,
    letterText: this.data.allCities[index].letter
  });
},
 
slideEnd: function (e) {
  var that = this;
  wx: setTimeout(function () {
    that.setData({
       isLetterHidden: true
    });
  }, 200);
}