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vue遞歸元件：樹形控件

1、遞歸元件-簡單樹形控件預覽及問題

vue遞歸元件：樹形控件

在編寫樹形元件時遇到的問題：

  • 元件如何才能遞歸調用？
  • 遞歸元件點選事件如何傳遞？

2、樹形控件基本結構及樣式 

<template>
  <ul class="vue-tree">
    <li class="tree-item">
      <div class="tree-content"><!--節點内容-->
        <div class="expand-arrow"></div><!--展開或收縮節點按鈕-->
        <div class="tree-label">國小</div><!--節點文本内容-->
      </div>
      <ul class="sub-tree"><!--子節點-->
        <li class="tree-item expand">
          <div class="tree-content">
            <div class="expand-arrow"></div>
            <div class="tree-label">國文</div>
          </div>
        </li>
        <li class="tree-item">
          <div class="tree-content">
            <div class="expand-arrow"></div>
            <div class="tree-label">數學</div>
          </div>
        </li>
      </ul>
    </li>
  </ul>
</template>

<style lang="stylus">
.vue-tree{
  list-style: none;
  padding: 0;
  margin: 0;
  .tree-item{
    cursor: pointer;
    transition: background-color .2s;
    .tree-content{
      position: relative;
      padding-left: 28px;
      &:hover{
        background-color: #f0f7ff;
      }
    }
    .expand-arrow{
      position: absolute;
      top: 0;
      left: 0;
      width: 28px;
      height: 28px;
      cursor: pointer;
      &::after{
        position: absolute;
        top: 50%;
        left: 50%;
        display: block;
        content: ' ';
        border-width: 5px;
        border-style: solid;
        border-color: transparent;
        border-left-color: #ccc;
        margin: -5px 0 0 -2.5px;
        transition: all .2s;
      }
    }
    &.expand{
      &>.tree-content{
        background-color: #f0f7ff;
        &>.expand-arrow{
          &::after{
            transform: rotate(90deg);
            margin: -2.5px 0 0 -5px;
          }
        }
      }
    }
    .tree-label{
      height: 28px;
      line-height: 28px;
      font-size: 14px;
    }
    .sub-tree{
      display: none;
      list-style: none;
      padding: 0 0 0 28px;
      margin: 0;
    }
    &.expand>.sub-tree{
      display: block;
    }
    &.no-child{
      &>.tree-content{
        &>.expand-arrow{
          display: none;
        }
      }
    }
  }
}
</style>

3、元件目錄及資料結構

目錄結構

vue-tree

  • VueTree.vue 樹形控件父元件
  • TreeItem.vue 樹形控件遞歸元件

樹形控件資料結構

let treeData = [
  {
    text: "一級", // 顯示的文字
    expand: false, // 預設是否展開
    children: [ // 子節點
      {
        text: "一級-1",
        expand: false,
      },
      {
        text: "一級-2",
        expand: false,
        children: [
          {
            text: "一級-2-1",
            expand: false,
          },
          {
            text: "一級-2-2",
            expand: false,
          }
        ]
      }
    ]
  }
];

3.1、TreeItem.vue 代碼 

<template>
  <li class="tree-item" :class="{expand: isExpand, 'no-child': !treeItemData.children || treeItemData.children.length  === 0}">
    <div class="tree-content" @click="_clickEvent">
      <div class="expand-arrow" @click.stop="expandTree()"></div>
      <div class="tree-label">{{treeItemData.text}}</div>
    </div>
    <ul class="sub-tree" v-if="treeItemData.children && treeItemData.children.length > 0">
      <!--TreeItem元件中調用TreeItem元件-->
      <TreeItem
        v-for="item in treeItemData.children"
        :tree-item-data="item"
        :key="uuid()"
        :tree-click-event="treeClickEvent"></TreeItem>
    </ul>
  </li>
</template>

<script>
  export default {
    name: "TreeItem",
    props: {
      treeItemData: {
        type: Object,
        default(){
          return {};
        }
      },
      // 節點點選事件
      treeClickEvent: {
        type: Function,
        default() {
          return function () {};
        }
      }
    },
    data(){
      return {
        // 節點是否展開
        isExpand: this.treeItemData.expand || false
      }
    },
    methods: {
      // 展開/收縮
      expandTree(flag){
        if(!this.treeItemData.children || this.treeItemData.children.length === 0){
          return;
        }
        if(typeof flag === 'undefined'){
          flag = !this.isExpand;
        }else{

          flag = !!flag;
        }
        this.isExpand = flag;
      },
      // 建立一個唯一id
      uuid(){
        let str = Math.random().toString(32);
        str = str.substr(2);
        return str;
      },
      // 節點點選事件
      _clickEvent(){
        // 如果有傳遞事件函數，則調用事件函數并傳遞目前節點資料及元件
        if(this.treeClickEvent && typeof this.treeClickEvent === 'function'){
          this.treeClickEvent(this.treeItemData, this);
        }
      }
    }
  }
</script>

3.1.1、解決 元件如何才能遞歸調用？ 問題

在元件模闆内調用自身必須明确定義元件的name屬性，并且遞歸調用時元件名稱就是name屬性。如在TreeItem.vue元件中元件的name名稱為'TreeItem'，那麼在template中調用時元件名稱就必須是<TreeItem>。

當然也可以全局注冊元件，具體可以檢視vue官方文檔 遞歸元件

3.1.2、解決 遞歸元件點選事件如何傳遞？ 問題

我這裡的解決方案是使用props将事件函數傳遞進來，在點選節點的時候調用事件函數，并把相應的資料傳遞進去。

之前也嘗試過使用$emit的形式并把資料傳遞過去，由于是遞歸元件，這樣一直$emit，到最外層時傳遞的資料就變了，比如傳遞是第3層節點的資料，到最後執行時資料就變成第1層節點的資料了

4、VueTree.vue 元件 

<template>
  <ul class="vue-tree">
    <TreeItem
        v-for="(item, index) in treeData"
        :key="index"
        :treeItemData="item"
        :tree-click-event="treeClickEvent"></TreeItem>
  </ul>
</template>

<script>
  import TreeItem from "./TreeItem";
  export default {
    name: "VueTreeMenu",
    components: {
      TreeItem
    },
    props: {
     // 樹形控件資料
      treeData: {
        type: Array,
        default(){
          return [];
        }
      },
      // 節點點選事件
      treeClickEvent: {
        type: Function,
        default() {
          return function () {};
        }
      }
    }
  }
</script>

<style lang="stylus">
.vue-tree{
  list-style: none;
  padding: 0;
  margin: 0;
  .tree-item{
    cursor: pointer;
    transition: background-color .2s;
    .tree-content{
      position: relative;
      padding-left: 28px;
      &:hover{
        background-color: #f0f7ff;
      }
    }
    .expand-arrow{
      position: absolute;
      top: 0;
      left: 0;
      width: 28px;
      height: 28px;
      cursor: pointer;
      &::after{
        position: absolute;
        top: 50%;
        left: 50%;
        display: block;
        content: ' ';
        border-width: 5px;
        border-style: solid;
        border-color: transparent;
        border-left-color: #ccc;
        margin: -5px 0 0 -2.5px;
        transition: all .2s;
      }
    }
    &.expand{
      &>.tree-content{
        background-color: #f0f7ff;
        &>.expand-arrow{
          &::after{
            transform: rotate(90deg);
            margin: -2.5px 0 0 -5px;
          }
        }
      }
    }
    .tree-label{
      height: 28px;
      line-height: 28px;
      font-size: 14px;
    }
    .sub-tree{
      display: none;
      list-style: none;
      padding: 0 0 0 28px;
      margin: 0;
    }
    &.expand>.sub-tree{
      display: block;
    }
    &.no-child{
      &>.tree-content{
        /*padding-left: 0;*/
        &>.expand-arrow{
          display: none;
        }
      }
    }
  }
}
</style>

5、使用樹形元件 

<template>
  <div class="app" id="app">
    <VueTree :tree-data="treeData2" :tree-click-event="treeClickEvent"></VueTree>
  </div>
</template>

<script>
import VueTree from "./components/vue-tree/VueTree";

export default {
  name: 'app',
  data(){
    return {
      treeData2: [
        {
          text: "一級", // 顯示的文字
          expand: false, // 預設是否展開
          children: [
            {
              text: "二級-1",
              expand: false,
            },
            {
              text: "二級-2",
              expand: false,
              children: [
                {
                  text: "三級-1",
                  expand: false,
                },
                {
                  text: "三級-2",
                  expand: false,
                  children: [
                    {
                      text: "四級-1",
                      expand: false,
                    }
                  ]
                }
              ]
            }
          ]
        },
        {
          text: "一級-2",
          expand: false
        }
      ]
    }
  },
  methods: {
    treeClickEvent(item, treeItem){
      console.log(item);
    }
  },
  components: {
    VueTree
  }
}
</script>
資料 遞歸 樹形控件 點選事件 遞歸調用
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