<view id='location_id' style="  padding: 0 40rpx; border:1rpx solid #DCDCDC;"></view>
<view class="{{ hideTop == true ? 'topnav' : '' }}">
 
  <view class="list-location" bindtap="showLocation">位置
     <van-icon name="arrow-down" />
  </view>
  <view style=" margin-top: 20rpx; padding: 0 40rpx; border:1rpx solid #DCDCDC;"></view>
</view>

.topnav{
    position: fixed;
    top: 0rpx;
    z-index:99;
    background: rgb(255,255,255);
    width: 100%;
}

//页面滚动监听
  onPageScroll: function (e) {
    let vm = this;
    var query = wx.createSelectorQuery()
    query.select('#location_id').boundingClientRect()
    query.selectViewport().scrollOffset()
    query.exec(function (res) {
      if (res[0].top < 0){  //res[0].top为location_id距离顶部的位置
        vm.setData({
          hideTop: true
        })
      }else{
        vm.setData({
          hideTop: false
        })
      }
    })
  },