<view class="container">
  <view class='anit {{show == 1?"show":(show == 2?"hide":"")}}'>请选择商品</view>
  <view bindtap='anniu'>点击弹出提示</view>
</view>

.container {
  height: 100%;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: space-between;
  padding: 200rpx 0;
  box-sizing: border-box;
} 
.anit{
  width: 100%;
  height: 70rpx;
  background: red;
  position: absolute;
  color: white;
  font-size: 30rpx;
  line-height: 70rpx;
  top: -70rpx;
  text-align: center;
}
.show{
  top: 0rpx;
  animation: show 0.2s;
  animation-timing-function:ease;
}
@keyframes show
{
from {top:-70rpx;}
to {top:0rpx;}
}
.hide{
  top: -70rpx;
  animation: hide 0.2s;
  animation-timing-function:ease;
}
@keyframes hide
{
from {top:0rpx;}
to {top:-70rpx;}
}

Page({
  data: {
    show: 0
  },
  onLoad: function () {
  },
  anniu:function(e){
    let that = this;
    this.setData({
      show:1
    })
    setTimeout(function () {
      that.setData({
        show: 2
      })
    }, 2000)
  }
})