wxmini/pages/piano/components/dropdownmenu/dropdownmenu.wxml

<view class="nav">
  <view class="nav-child borders {{source_open? 'active' : ''}}" bindtap="tapSourceNav" hidden='{{dropDownMenuSourceData.length > 0 ? false : true}}' data-nav="2">
    <view class="nav-title">{{selected_source_name.length > 0 ?selected_source_name : dropDownMenuTitle[0]}}</view>
    <view class="flexEmpty"></view>
    <view class="icon"></view>
  </view>

  <view class="container container_hd {{source_open ? 'show' : 'disappear'}} ">
  <view class='z-height'>
    <view>
      <block wx:for="{{dropDownMenuSourceData}}" wx:key="unique">
        <view class="sortitem {{selected_source_id==item.id ? ' active ' : ' '}}" data-model='{{item}}' bindtap='selectSourceItem'> {{item.title}}</view>
      </block>
    </view>
  </view>
</view>
</view>