前言

项目中要实现类似与vant的DropdownMenu:下拉菜单。看了vans 的效果 其实也没什么难度，于是动手鲁了一个这样的组件。
项目的技术栈为react全家桶+material UI + ant Design mobile。

vans的效果

我自己实现的效果

思路

常规做法获取dom元素，动态修改选中dom的innerHtml。
当然这种方式不是react推荐的

我的做法既然react不推荐直接操作dom元素，那可以采用动态动态修改class的方式达到效果，例如：

let cls ="normal"
div未被选中时
<div className={cls}/> 
div被选中时
cls+=" current"
<div className ={cls}>

实现步骤

顶部tab采用三个div的方式布局，由于需要动态修改tab上的标题，所以定义一个数组，reducer中的tab数据结构如下

let tabs = {};
tabs[TABKAY.AREA] = {
key: TABKAY.AREA,
text: "全部区域",
obj: {}
};
tabs[TABKAY.SORT] = {
key: TABKAY.SORT,
text: "综合排序",
obj: {}
};
tabs[TABKAY.FILTER] = {
key: TABKAY.FILTER,
text: "筛选",
obj: SX
};
const initialState = {
areas: [{ id: "", name: "全部区域" }],
tabs: tabs,
actionKey: TABKAY.AREA,// 标识了当前选中tab
closePanel: true // 标识panel div 是否显示
};

tabUI组件的页面容器渲染方法

renderTabs() {
const { tabs, actionKey, closePanel } = this.props;
//---------
if (!closePanel) {
 fixedBody();
} else {
 looseBody();
}
//---------

let aray = [];
for (let key in tabs) {
 let item = tabs[key];
 let cls = item.key + " item";
 if (item.key === actionKey && !closePanel) {
  cls += " current";
 }

 aray.push(
  <div className={cls} key={item.key} onClick={() => this.onChangeTab(item.key)}>
   {item.text}
  </div>);
}

return aray;
}

样式：这里边有个技巧，就是利用了css元素选择器的伪类的方式巧妙实现了箭头以及箭头的旋转动画

.item {
flex: 1;
font-size: 15px;
border-right: 0.5px solid #eaeaea;
text-align: center;

&:last-child {
 border: none;
}

&.AREA:after, &.SORT:after, &.FILTER:after {
 content: "";
 display: inline-block;
 width: 5px;
 height: 5px;
 margin-bottom: 2px;
 margin-left: 6px;
 border: 2px solid #666;
 border-width: 0 2px 2px 0;
 transform: rotate(45deg);
 -webkit-transform: rotate(45deg);
 -webkit-transition: .3s;
 transition: .3s;
}

&.current {
 color: #0084ff;
}

&.current:after {
 border-color: #0084ff;
 transform: rotate(225deg);
 -webkit-transform: rotate(225deg);
}

chrome 查看元素

全部区域tab被选中：

综合tab被选中

每次点击不同的tab时 都会自动的渲染current这个css样式，这样就实现了下拉菜单的功能。

完整代码

/**
 * Class:
 * Author: miyaliunian
 * Date: 2019/5/26
 * Description: tabs 选择器
 * 医院列表
 */
import React, { Component } from "react";
import { ZHPX, TABKAY } from "@api/Constant";
//Util
import { fixedBody, looseBody } from "@utils/fixRollingPenetration";
//Redux
import { connect } from "react-redux";
import { bindActionCreators } from "redux";
import { actions as tabActions, getTabs, getAreasList, getActionKey, getClosePanel } from "@reduxs/modules/tabs";
import { actions as hospitalActions,} from "@reduxs/modules/hospital";

//样式
import "./tabs.less";

class Tabs extends Component {
 
 /**
  * 变化当前点击的item状态 同时filter 请求
  * @param filterItem 当前选中的元素
  * @param key  哪个tab是选中状态
  */
 changeDoFilter(filterItem, key, event) {
  const { tabActions: { changeFilter }, hospitalActions:{filterHosiContentList} } = this.props;
  event.stopPropagation();
  changeFilter(filterItem, key, (filter) => {
   filterHosiContentList(filter);
  });
 }

 /**
  * 筛选tab确定按钮
  * @param event
  */
 filterPanel(event) {
  const {tabActions:{closePanelAction}, tabs,hospitalActions:{filterHosiContentList}} = this.props;
  event.stopPropagation();
  closePanelAction(()=>{
   filterHosiContentList(tabs)
  })
 }

 /**
  * 点击切换Tab
  * @param key
  */
 onChangeTab(key) {
  const { actionKey,tabActions: { changeTab } } = this.props;
  let closePanel = false;
  //如果前后点击的是同一个tab 就关闭panel
  if (actionKey === key && !this.props.closePanel) {
   closePanel = true;
  }
  closePanel ? looseBody() : fixedBody();
  changeTab(key, closePanel);
 }

 /**
  * 渲染顶部tab
  */
 renderTabs() {
  const { tabs, actionKey, closePanel } = this.props;
  //---------
  if (!closePanel) {
   fixedBody();
  } else {
   looseBody();
  }
  //---------

  let aray = [];
  for (let key in tabs) {
   let item = tabs[key];
   let cls = item.key + " item";
   if (item.key === actionKey && !closePanel) {
    cls += " current";
   }

   aray.push(
    <div className={cls} key={item.key} onClick={() => this.onChangeTab(item.key)}>
     {item.text}
    </div>);
  }

  return aray;
 }

 /**
  * 全部区域
  * @returns {*}
  */
 renderAreaContent() {
  const { areasList } = this.props;
  return areasList.map((item, index) => {
   let cls = item.active + " area-item";
   return (
    <li key={index} className={"area-item"} onClick={(e) => this.changeDoFilter(item, TABKAY.AREA, e)}>
     {item.name}
    </li>
   );
  });
 }


 /**
  * 全部排序
  * @returns {any[]}
  */
 renderSORTContent() {
  let sortList = ZHPX;
  return sortList.map((item, index) => {
   let cls = item.action ? "type-item active" : "type-item";

   return (
    <li key={index} className={cls} onClick={(e) => this.changeDoFilter(item, TABKAY.SORT, e)}>
     {item.name}
    </li>
   );
  });
 }


 /**
  * 筛选
  * @returns {*}
  */

 renderFilterInnerContent(items/*filterList*/) {
  return items.map((item, index) => {
   let cls = "cate-box";
   if (item.active) {
    cls += " active";
   }

   return (
    <div key={index} className={cls} onClick={(e) => this.changeDoFilter(item, TABKAY.FILTER, e)}>
     {item.name}
    </div>
   );
  });

 }

 renderFILTERContent() {
  let filterList = [];
  const { tabs } = this.props;
  filterList = tabs[TABKAY.FILTER].obj;
  return filterList.map((item, index) => {
   return (
    <li key={index} className={"filter-item"}>
     <p className={"filter-title"}>{index == 0 ? `医院类型: ${item.groupTitle}` : `医院等级: ${item.groupTitle}`}</p>
     <div className={"item-content"}>
      {this.renderFilterInnerContent(item.items, filterList)}
     </div>
    </li>
   );
  });
 }

 /**
  * 渲染过滤面板
  */
 renderContent() {
  const { tabs, actionKey } = this.props;
  let array = [];
  for (let key in tabs) {
   let item = tabs[key];
   let cls = item.key + "-panel";
   if (item.key === actionKey) {
    cls += " current";
   }

   // 全部区域
   if (item.key === TABKAY.AREA) {
    array.push(
     <ul key={item.key} className={cls}>
      {this.renderAreaContent()}
     </ul>
    );
   } else if (item.key === TABKAY.SORT) {
    // 综合排序
    array.push(
     <ul key={item.key} className={cls}>
      {this.renderSORTContent()}
     </ul>
    );
   } else if (item.key === TABKAY.FILTER) {
    // 筛选
    array.push(
     <ul key={item.key} className={cls}>
      {this.renderFILTERContent()}
      <div className={"filterBtn"} onClick={(e) => this.filterPanel(e)}>
       确定
      </div>
     </ul>
    );
   }

  }
  return array;
 }


 render() {
  const { closePanel, tabActions: { closePanelAction } } = this.props;
  let cls = "panel";
  if (!closePanel) {
   cls += " show";
  } else {
   cls = "panel";
  }
  return (
   <div className={"tab-header"}>
    <div className={"tab-header-top border-bottom"}>
     {this.renderTabs()}
    </div>
    <div className={cls} onClick={() => closePanelAction(()=>{})}>
     <div className={"panel-inner"}>
      {this.renderContent()}
     </div>
    </div>
   </div>
  );
 }


 componentDidMount() {
  const { areasList, tabActions: { loadAreas } } = this.props;
  if (areasList && areasList.length !== 1) {
   return;
  }
  loadAreas();
 }
}

const mapStateToProps = state => {
 return {
  areasList: getAreasList(state),
  tabs: getTabs(state),
  actionKey: getActionKey(state),
  closePanel: getClosePanel(state)
 };
};

const mapDispatchToProps = dispatch => {
 return {
  tabActions: bindActionCreators(tabActions, dispatch),
  hospitalActions: bindActionCreators(hospitalActions, dispatch)
 };
};

export default connect(mapStateToProps, mapDispatchToProps)(Tabs);