小程序搜索框下拉和上滑位置改变

下拉要跟着下拉，凸显上面的下拉动画，上滑的时候固定搜索框到顶部，搜索组件用的vant

.page {

  color: #666;

  background-color: #f6f6f6;

  min-height: 100vh;

  overflow: auto;

  position: relative;

  padding-top: 100rpx;

}

.absolute{
    position: absolute;
}

.search-box {

  width: 100%;

  position: fixed;

  top: 0;

}

  onPageScroll(event) {
    if (event.scrollTop == 0) {
      this.setData({
        absolute: 'absolute'
      })
    } else {
      if (this.data.absolute != '') {
        this.setData({
          absolute: ''
        })
      }
    }
  }

<view class="page">
    <view class="search-box {{absolute}}">
        <van-search value="{{ value }}" shape="round" placeholder="名称" use-action-slot bind:change="onChange" bind:search="onSearch" right-icon="search" left-icon="">
            <view slot="action" bind:tap="filterSel" class="filter-box">
                <van-icon name="/assets/icons/filter.png" size="36rpx" />筛选
            </view>
        </van-search>
    </view>
        <view>listdata</view>
</view>