<view style="width: 90%; height: 300rpx; background: #f0f0f0; margin: 30rpx auto;"></view>
<view style="width: 90%; height: 300rpx; background: #f0f0f0; margin: 30rpx auto;"></view>


<view class="navbar-wrap">
 <view class="column {{isFixedTop" id="navbar">
  <view class="block active">新品推荐</view>
  <view class="block">限时优惠</view>
  <view class="block">火爆热搜</view>
  <view class="block">猜你喜欢</view>
 </view>
 <!-- 用于吸顶后 占位用的 -->
 <view class="column" wx:if="{{isFixedTop}}"></view>
</view>


<block wx:for="{{20}}" wx:key="list">
 <view style="width: 100%; height: 120rpx; background: #f0f0f0; margin: 20rpx auto;"></view>
</block>

view, text {
 box-sizing: border-box;
 -moz-box-sizing: border-box;
 -webkit-box-sizing: border-box;
}

.navbar-wrap {
 width: 100%;
}

.navbar-wrap .column {
 width: 100%;
 height: 80rpx;
 display: flex;
 flex-direction: row;
 align-items: center;
 justify-content: space-around;
 background: #fff;
 border-bottom: solid 1px #eee;

 top: 0;
 left: 0;
 z-index: 100;
}

.navbar-wrap .column.fixed {
 position: fixed;
}

/* 以下的代码不重要 */

.navbar-wrap .column .block {
 width: 25%;
 height: 80rpx;
 line-height: 80rpx;
 text-align: center;
 font-size: 30rpx;
 color: #333;
 letter-spacing: 1px;
 position: relative;
}

.navbar-wrap .column .block::after {
 content: "";
 width: 60%;
 height: 3px;
 border-radius: 2px;
 position: absolute;
 bottom: 0;
 left: 50%;
 transform: translateX(-50%);
 background: transparent;
}

.navbar-wrap .column .block.active {
 color: #1490ce;
 font-weight: bold;
}

.navbar-wrap .column .block.active::after {
 background: linear-gradient(160deg, rgba(8, 220, 230, 0.7) 10%, rgba(0, 140, 255, 0.7) 90%);
}

Page({
 data: {
  navbarInitTop: 0, //导航栏初始化距顶部的距离
  isFixedTop: false, //是否固定顶部
 },

 /**
  * 生命周期函数--监听页面加载
  */
 onLoad: function(options) {

 },

 /**
  * 生命周期函数--监听页面显示
  */
 onShow: function() {
  var that = this;

  if (that.data.navbarInitTop == 0) {

   //获取节点距离顶部的距离
   wx.createSelectorQuery().select('#navbar').boundingClientRect(function(rect) {
    if (rect && rect.top > 0) {
     var navbarInitTop = parseInt(rect.top);
     that.setData({
      navbarInitTop: navbarInitTop
     });
    }
   }).exec();

  }
 },

 /**
  * 监听页面滑动事件
  */
 onPageScroll: function(e) {
  var that = this;
  var scrollTop = parseInt(e.scrollTop); //滚动条距离顶部高度

  //判断'滚动条'滚动的距离 和 '元素在初始时'距顶部的距离进行判断
  var isSatisfy = scrollTop >= that.data.navbarInitTop ? true : false;
  //为了防止不停的setData, 这儿做了一个等式判断。 只有处于吸顶的临界值才会不相等
  if (that.data.isFixedTop === isSatisfy) {
   return false;
  }

  that.setData({
   isFixedTop: isSatisfy
  });
 }


})