vue navbar tabbar导航条根据位置移动实现定位、颜色过渡动画效果的代码

vant文档：Vant 2 – Mobile UI Components built on Vue

实现效果： 

代码实现：

1.navbar、tabbar顶部导航过渡效果、颜色过渡；

<div class="mallHead">
        <van-nav-bar :title="titleName" fixed @click-left="onClickLeft" :style="style" safe-area-inset-top>
          <template #left>
            <van-icon name="arrow-left" size="22px" color="#024EE0" />
          </template>
        </van-nav-bar>
        <div class="top"></div>
</div>

<div :class="indexTop>220?'menuActive':'dropdown-menu'" >
        <van-dropdown-menu>
          <van-dropdown-item v-model="amountValue" :options="amountOption" />
          <van-dropdown-item v-model="integralValue" :options="integralOption" />
          <van-dropdown-item v-model="goodsValue" :options="goodsOption" />
        </van-dropdown-menu>
</div>

css样式 

.mallHead ::v-deep.van-nav-bar{
  background: none;
  .van-icon-arrow-left{
    color:#fff !important;
  }
  .van-nav-bar__title{
    color:#fff;
  }
}
.mallHead ::v-deep.van-nav-bar::after{
  border: 0;
}

.menuActive{
  box-shadow: none;
  background:#fff;
  width: 100%;
  position: fixed;
  top: 92px;
  left: 0;
  z-index: 1;
}

 2.定义data

data(){
    return {
        style:null,
        indexTop:0,// 滚动条高度
        amountValue:0,
        amountOption:[
            { text: '兑换量从高到底', value: 0 },
            { text: '积分从低到高', value: 1 },
            { text: '积分从高到低', value: 2 },
          ],
        .......
    }
}

3.methods方法定义 

mounted(){
    window.addEventListener('scroll', this.handleScroll,true);
  },
  destroyed() {
    window.removeEventListener('scroll', this.handleScroll);
  },

定义handleScroll方法

Math.abs(Math.round(this.indexTop)) / 100; 自行定义

handleScroll(){
      this.indexTop = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop; // 计算出移动位置
      const opacity = Math.abs(Math.round(this.indexTop)) / 100; // 根据位置移动动态设置背景透明度
      this.style = { background: `rgba(253,85,39,${opacity})`};
}