微信小程序中实现吸顶效果(流畅、不卡顿)

<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?'fixed':''}}" 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
    });
  }


})