<view class='top'>
  <view class='top-text'> 选择接收班级</view>
  <!-- 下拉框 -->
  <view class='top-selected' bindtap='bindShowMsg'>
   <text>{{grade_name}}</text>
   <image src='/images/icon/down.png'></image>
  </view>
  <!-- 下拉需要显示的列表 -->
  <view class="select_box" wx:if="{{select}}">
   <view wx:for="{{grades}}" wx:key="unique">
    <view class="select_one" bindtap="mySelect" data-name="{{item}}">{{item}}</view>
   </view>
  </view>
 </view>

/* 顶部 */
.top{
 width: 100vw;
 height: 80rpx;
 padding: 0 20rpx;
 line-height: 80rpx;
 font-size: 34rpx;
 border-bottom: 1px solid #000;
}
.top-text{
 float: left
}
/* 下拉框 */
.top-selected{
  width: 50%;
  display: flex;
  float: right;
  align-items: center;
  justify-content: space-between;
  border: 1px solid #ccc;
  padding: 0 10rpx;
  font-size: 30rpx;
}
/* 下拉内容 */
.select_box {
  background-color: #fff;
  padding: 0 20rpx;
  width: 50%;
  float: right;
  position: relative;
  right: 0;
  z-index: 1;
  overflow: hidden;
  text-align: left;
  animation: myfirst 0.5s;
  font-size: 30rpx;
}
.select_one {
  padding-left: 20rpx;
  width: 100%;
  height: 60rpx;
  position: relative;
  line-height: 60rpx;
  border-bottom: 1px solid #ccc;
}
/* 下拉过度效果 */
@keyframes myfirst {
  from {
    height: 0rpx;
  }
 
  to {
    height: 210rpx;
  }
}
/* 下拉图标 */
.top-selected image{
 height:50rpx;
 width:50rpx;
 position: absolute;
 right: 0rpx;
 top: 20rpx;
}

 /**
  * 页面的初始数据
  */
 data: {
  select:false,
  grade_name:'--请选择--',
  grades: [
    '猛犸机器人1班',
    '猛犸机器人2班',
    '口才1班',
   ]
 },/**
 * 点击下拉框
 */
 bindShowMsg() {
  this.setData({
   select: !this.data.select
  })
 },
/**
 * 已选下拉框
 */
 mySelect(e) {
  console.log(e)
  var name = e.currentTarget.dataset.name
  this.setData({
   grade_name: name,
   select: false
  })
 },