<view class='select_box'>
 <view class='select' catchtap='selectTap'>
  <text class='select_text'>{{selectData[index]}}</text>
  <image class='select_img {{show&&"select_img_rotate"}}' src='/image/gobottom.png'></image>   
 </view>
 <view class='option_box' style='height:{{show"border:0;"}}' wx:for='{{selectData}}' wx:key='this' data-index='{{index}}' catchtap='optionTap'>{{item}}</text>
 </view>
</view>
<!--
 show&&"select_img_rotate"-----给显示框右边的下拉箭头添加动画

 height:{{show"border:0;"-----取消下拉选项的最后一个的下边框
 -->

page{
 background: #f3f7f7;
}
.select_box{
 background: #fff;
 width: 80%;
 margin: 30rpx auto;
 position: relative;
}
.select{
 box-sizing: border-box;
 width: 100%;
 height: 70rpx;
 border:1px solid #efefef;
 border-radius: 8rpx;
 display: flex;
 align-items: center;
 padding: 0 20rpx;
}
.select_text{
 font-size: 30rpx;
 flex: 1;
}
.select_img{
 width: 40rpx;
 height: 40rpx;
 display: block;
 transition:transform 0.3s;
}
.select_img_rotate{
 transform:rotate(180deg); 
}
.option_box{
 position: absolute;
 top: 70rpx;
 width: 100%;
 border:1px solid #efefef;
 box-sizing: border-box;
 height: 0;
 overflow-y: auto;
 border-top: 0;
 background: #fff;
 transition: height 0.3s;
}
.option{
 display: block;
 line-height: 40rpx;
 font-size: 30rpx;
 border-bottom: 1px solid #efefef;
 padding: 10rpx;
}

Page({

 data: {
 show:false,//控制下拉列表的显示隐藏，false隐藏、true显示
 selectData:['1','2','3','4','5','6'],//下拉列表的数据
 index:0//选择的下拉列表下标
 },
 // 点击下拉显示框
 selectTap(){
 this.setData({
  show: !this.data.show
 });
 },
 // 点击下拉列表
 optionTap(e){
 let Index=e.currentTarget.dataset.index;//获取点击的下拉列表的下标
 this.setData({
  index:Index,
  show:!this.data.show
 });
 },
 onLoad: function (options) {
 
 }

})