Vue render函数实战--实现tabs选项卡组件

用过 Element ui 库的童鞋肯定知道 <el-tabs> 组件，简单、好用、可以自定义标签页，不知道广大童鞋们在刚开始使用 <el-tabs> 组件的时候有没有想过它是如何实现的？我咋刚开始使用 <el-tabs> 组件的时候就有去想过，也想去实现一个超级简单的tabs选项卡组件，无奈当时功力不够，未能实现。最近的一个简单项目中正好要用到选项卡组件，由于项目简单也就没有使用任何第三方库，于是就自己动手写了个选项卡组件。

1、实现tabs选项卡组件的思考

<el-tabs v-model="activeName" @tab-click="handleClick">
    <el-tab-pane label="用户管理" name="first">用户管理</el-tab-pane>
    <el-tab-pane label="配置管理" name="second">配置管理</el-tab-pane>
    <el-tab-pane label="角色管理" name="third">角色管理</el-tab-pane>
    <el-tab-pane label="定时任务补偿" name="fourth">定时任务补偿</el-tab-pane>
</el-tabs>

问题：

1. 如何根据 <el-tab-pane> 来生成标签页？
2. 如何过滤 <el-tabs> 组件中的子元素，使得在使用的时候只显示 <el-tab-pane> ，而不会显示其他组件或 div 之类的元素？

2、实现思路

1. 想根据 <el-tab-pane> 来生成标签页就需要使用到 <slot> ，使用 <slot> 用 <template> 的形式肯定是不行的，因为无法获取到 <slot> 的数量；使用 <template> 的形式行不通，那就只有使用 render函数 了
2. 过滤 <el-tabs> 组件中的子元素也需要使用render函数

3、代码实现

index.js

import PTabs from './PTabs';
import PTabPane from './PTabPane';

export default function tabsInstall(Vue) {
  if(tabsInstall.installed){
    return;
  }
  Vue.component('PTabs', PTabs);
  Vue.component('PTabPane', PTabPane);
}

PTabs.vue

<script>
  import PTabNav from './PTabNav';
  export default {
    name: "PTabs",
    props: {
      value: {
        type: [String, Number],
        default: ''
      },
      beforeClick: {
        type: Function,
        default(){
          return function () {};
        }
      }
    },
    components: {
      PTabNav
    },
    data(){
      return {
        pTabPanes: [],
        currentName: this.value || 0
      }
    },
    methods: {
      addPane(pane){
        this.pTabPanes.push(pane);
        if(!this.currentName){
          this.setCurrentName(this.pTabPanes[0].name);
        }
      },
      removePane(pane){
        let index = this.pTabPanes.indexOf(pane);
        if(index > -1){
          this.pTabPanes.splice(index, 1);
        }
      },
      setCurrentName(name){
        if(this.currentName !== name){
          this.currentName = name;
          this.$emit('input', name);
        }
      },
      // 标签页点击事件
      handTabNavClick(name, pane, e){
        if(this.currentName === name || pane.disabled){
          return;
        }

        let before = this.beforeClick();
        if(before && before.then){
          before.then(() => {
            this.setCurrentName(name);
            this.$emit('tabClick', pane, e);
          })
        }else{
          this.setCurrentName(name);
          this.$emit('tabClick', pane, e);
        }
      }
    },
    watch: {
      value(newVal){
        this.setCurrentName(newVal);
      },
      currentName(){
        this.$nextTick(() => {
          this.$refs.p_tab_nav.scrollToActiveTab();
        });
      }
    },
    render(h) {
      let {$scopedSlots} = this;
      let $default = $scopedSlots.default();
      let qTabPanes = $default.map(item => {
        /* 过滤<PTabs>xxx</PTabs>中传递的xxx内容。这里只接收<PTabPane>组件，因为我们需要根据<PTabPane>组件的数量来生成
         * <PTabNav>组件，如果参差了其它节点则会导致不能正确生成<PTabNav>组件 */
        if(item.componentOptions && item.componentOptions.tag === 'PTabPane'){
          return item;
        }
      });

      let qTab = h('PTabNav', {
        props: {
          // 将tab-pane传递给 <PTabNav>组件，<PTabNav>组件就知道要有多少个tab-item了
          tabPanes: this.pTabPanes,
          handTabNavClick: this.handTabNavClick
        },
        ref: 'p_tab_nav'
      });
      let qTabBody = h('div', {
        staticClass: 'p-tabs_content'
      }, qTabPanes);


      console.log($default)
      return h('div', {
        staticClass: 'p-tabs'
      }, [qTab, qTabBody]);
    },
    mounted() {
      //console.log(this)
      this.$nextTick(() => {
        this.$refs.p_tab_nav.scrollToActiveTab();
      });
    }
  }
</script>

<style lang="stylus">
.p-tabs{
  .p-tabs_header{
    position: relative;
    margin-bottom: 15px;
    &.is-scrollable{
      padding-left: 20px;
      padding-right: 20px;
    }
  }
  .p-tabs_nav-prev,
  .p-tabs_nav-next{
    position: absolute;
    top: 0;
    width: 20px;
    height: 100%;
    display: none;
    &::before{
      position: absolute;
      content: ' ';
      font-size: 0;
      line-height: 0;
      width: 10px;
      height: 10px;
      top: 50%;
      left: 50%;
      border-top: 1px solid #eee;
      border-left: 1px solid #eee;
      margin: -5px 0 0 -5px;
    }
    cursor: pointer;
    &.disabled{
      cursor: default;
      border-color: #aaa;
    }
  }
  .p-tabs_nav-prev{
    left: 0;
    &:before{
      transform: rotate(-45deg);
    }
  }
  .p-tabs_nav-next{
    right: 0;
    &:before{
      transform: rotate(135deg);
    }
  }
  .p-tabs_header{
    &.is-scrollable{
      .p-tabs_nav-prev,
      .p-tabs_nav-next{
        display: block;
      }
    }
  }
  .p-tabs_nav-scroll{
    overflow: hidden;
  }
  .p-tabs_nav-list{
    position: relative;
    float: left;
    white-space: nowrap;
    transition: transform .3s;
  }
  .p-tabs_nav-item{
    display: inline-block;
    height: 40px;
    line-height: 40px;
    padding: 0 20px;
    color: #fff;
    cursor: pointer;
    &.active,
    &:hover{
      color: #ffb845;
    }
    &.disabled{
      cursor: not-allowed;
      color: #aaa;
      &:hover{
        color: #aaa;
      }
    }
  }
  .p-tabs_content{
    position: relative;
    overflow: hidden;
  }
  .p-tabs-pane{
    color: #fff;
  }
}
</style>

PTabPane.vue

<template>
  <div class="p-tabs-pane" v-show="show">
    <slot></slot>
  </div>
</template>

<script>
  export default {
    name: "PTabPane",
    props: {
      label: {
        type: String,
        default: ''
      },
      name: {
        type: [String, Number],
        default: ''
      },
      disabled: {
        type: Boolean,
        default: false
      }
    },
    data(){
      return {
        loaded: false
      }
    },
    computed: {
      show(){
        if(this.$parent.currentName === this.name){
          if(!this.loaded){
            this.loaded = true;
          }
          return true;
        }
        return false;
      }
    },
    watch: {
      label(){
        // label更新的时候强制更新父组件，以触发PTabNav才能更新
        this.$parent.$forceUpdate();
      }
    },
    mounted() {
      // 当当前组件创建的时候将当前组件添加到父组件的pTabPanes中，以触发PTabNav才能更新
      this.$parent.addPane(this);
    },
    destroyed() {
      if(this.$el && this.$el.parentNode){
        this.$el.parentNode.removeChild(this.$el);
      }
      // 当当前组件销毁时需从父组件中的pTabPanes中移除当前组件，以触发PTabNav才能更新
      this.$parent.removePane(this);
    }
  }
</script>

PTabNav.vue

<script>
  function noop() {};

  export default {
    name: "PTabNav",
    props: {
      tabPanes: {
        type: Array,
        default(){
          return [];
        }
      },
      handTabNavClick: {
        type: Function,
        default(){
          return function () {};
        }
      }
    },
    data(){
      return {
        navPrevDisabled: true,
        navNextDisabled: true,
        // 控制左右箭头显示
        scrollable: false,
        listOffset: 0
      }
    },
    methods: {
      navPrevClickEvent(){
        if(!this.navPrevDisabled){
          let navScrollW = this.$refs.nav_scroll.offsetWidth;
          let navListW = this.$refs.nav_list.offsetWidth;
          let maxTransformX = 0;
          let transformX = this.listOffset - navScrollW;
          if(transformX < maxTransformX){
            transformX = maxTransformX;
          }
          if(transformX === this.listOffset){
            return;
          }
          console.log('上一页按钮点击了', transformX);
          this.listOffset = transformX;
          if(transformX === 0){
            this.navPrevDisabled = true;
            this.navNextDisabled = false;
          }else if(transformX === (navListW - navScrollW)){
            this.navPrevDisabled = false;
            this.navNextDisabled = true;
          }else{
            this.navPrevDisabled = false;
            this.navNextDisabled = false;
          }
        }
      },
      navNextClickEvent(){
        if(!this.navNextDisabled){
          let navScrollW = this.$refs.nav_scroll.offsetWidth;
          let navListW = this.$refs.nav_list.offsetWidth;
          let maxTransformX = navListW - navScrollW;
          let transformX = this.listOffset + navScrollW;
          if(transformX > maxTransformX){
            transformX = maxTransformX;
          }
          if(transformX === this.listOffset){
            return;
          }
          console.log('下一页按钮点击了', transformX);
          this.listOffset = transformX;
          if(transformX === 0){
            this.navPrevDisabled = true;
            this.navNextDisabled = false;
          }else if(transformX === (navListW - navScrollW)){
            this.navPrevDisabled = false;
            this.navNextDisabled = true;
          }else{
            this.navPrevDisabled = false;
            this.navNextDisabled = false;
          }
        }
      },
      // 计算 .p-tabs_nav-list 是否溢出
      calculateListSpilled(){
        let navScrollW = this.$refs.nav_scroll.offsetWidth;
        let navListW = this.$refs.nav_list.offsetWidth;
        if(navScrollW < navListW){
          this.scrollable = true;
        }else{
          if(this.listOffset > 0){
            this.listOffset = 0;
          }
          this.scrollable = false;
        }
      },
      // 滚动条滚动到激活的tab
      scrollToActiveTab(){
        if(this.scrollable){
          this.$nextTick(() => {
            let navScrollW = this.$refs.nav_scroll.offsetWidth;
            let navList = this.$refs.nav_list;
            let activeTab = navList.querySelector('.active');
            let activeTabOffsetLeft = 0;
            if(activeTab){
              activeTabOffsetLeft = activeTab.offsetLeft;
            }

            let transformX = activeTabOffsetLeft + activeTab.offsetWidth - navScrollW;

            transformX = transformX < 0 ? 0 : transformX;
            this.listOffset = transformX;
            if(transformX === 0){
              this.navPrevDisabled = true;
              this.navNextDisabled = false;
            }else if(transformX === (navList.offsetWidth - navScrollW)){
              this.navPrevDisabled = false;
              this.navNextDisabled = true;
            }else{
              this.navPrevDisabled = false;
              this.navNextDisabled = false;
            }
          });
        }
      }
    },
    computed: {
      listOffsetTran(){
        console.log('dddd',`translateX(-${this.listOffset}px);`)
        return {
          transform: `translateX(-${this.listOffset}px)`
        }
      }
    },
    render(h) {
    /*dom结构
    <div class="p-tabs_header is-scrollable">
        <span class="p-tabs_nav-prev disabled"></span>
        <span class="p-tabs_nav-next"></span>
      <div class="p-tabs_nav-scroll">
        <div class="p-tabs_nav-list">
          <div class="p-tabs_nav-item active">全部</div>
          <div class="p-tabs_nav-item disabled">技术教学</div>
          <div class="p-tabs_nav-item">新手教学</div>
        </div>
      </div>
    </div>
    */
      let navPrev = h('span', {
        staticClass: 'p-tabs_nav-prev',
        'class': {
          disabled: this.navPrevDisabled
        },
        on: {
          click: this.navPrevClickEvent
        }
      });
      let navNext = h('span', {
        staticClass: 'p-tabs_nav-next',
        'class': {
          disabled: this.navNextDisabled
        },
        on: {
          click: this.navNextClickEvent
        }
      });
      // 生成标签页
      let navItems = this.tabPanes.map(item => {
        let $labelSlot = item.$scopedSlots.label ? item.$scopedSlots.label() : null;
        let labelContent = $labelSlot ? $labelSlot : item.label;
        return h('div', {
          staticClass: 'p-tabs_nav-item',
          'class': {
            active: this.$parent.currentName === item.name,
            disabled: item.disabled,
          },
          on: {
            click: (e) => {
              this.handTabNavClick(item.name, item, e);
            }
          }
        }, [labelContent]);
      });
      let navScroll = h('div', {
        staticClass: 'p-tabs_nav-scroll',
        ref: 'nav_scroll'
      }, [
        h('div', {
          staticClass: 'p-tabs_nav-list',
          ref: 'nav_list',
          style: this.listOffsetTran
        }, [navItems])
      ]);

      return h('div', {
        staticClass: 'p-tabs_header',
        'class': {
          'is-scrollable': this.scrollable
        },
      }, [navPrev, navNext, navScroll]);
    },
    updated(){
      this.calculateListSpilled();
    },
    mounted() {
      this.calculateListSpilled();
    }
  }
</script>

4、使用

main.js

// 引入tabs组件
import tabs from './components/p-tabs';
// 全局注册p-tabs组件
Vue.use(tabs);

页面中使用

<PTabs v-model="activeName">
    <PTabPane label="用户管理" name="first">用户管理</PTabPane>
    <PTabPane label="配置管理" name="second">配置管理</PTabPane>
    <PTabPane label="角色管理" name="third">角色管理</PTabPane>
    <PTabPane label="定时任务补偿" name="fourth">定时任务补偿</PTabPane>
</PTabs>