template这样写：

<div class="outer-container">
    <div class="inner-container" v-for="(item,index) in treeLists" v-key="item.id">
        <div class="classifyRow" @click="vm.changeClassify(item.id, index)" :class="{'activity':index == classifyIndex}">{{item.name}}
        </div>
    </div>
</div>

changeClassify: (type, index) => {
    this.classifyIndex = index;
}

通过控制每一次点击改变classifyIndex 的值，来让 activity 为 true ，非常简单