<template>
 <el-select :value="valueTitle" :clearable="clearable" @clear="clearHandle">
  <el-option :value="valueTitle" :label="valueTitle">
   <el-tree id="tree-option"
    ref="selectTree"
    :accordion="accordion"
    :data="options"
    :props="props"
    :node-key="props.value"  
    :default-expanded-keys="defaultExpandedKey"
    @node-click="handleNodeClick">
   </el-tree>
  </el-option>
 </el-select>
</template>

<script>
export default {
 name: "el-tree-select",
 props:{
  /* 配置项 */
  props:{
   type: Object,
   default:()=>{
    return {
     value:'id',       // ID字段名
     label: 'title',     // 显示名称
     children: 'children'  // 子级字段名
    }
   }
  },
  /* 选项列表数据(树形结构的对象数组) */
  options:{
   type: Array,    
   default: ()=>{ return [] }
  },
  /* 初始值 */
  value:{
   type: Number,
   default: ()=>{ return null }
  },
  /* 可清空选项 */
  clearable:{
   type:Boolean,
   default:()=>{ return true }
  },
  /* 自动收起 */
  accordion:{
   type:Boolean,
   default:()=>{ return false }
  },
 },
 data() {
  return {
   valueId:this.value,  // 初始值
   valueTitle:'',
   defaultExpandedKey:[]  
  }
 },
 mounted(){
  this.initHandle()
 },
 methods: {
  // 初始化值
  initHandle(){
   if(this.valueId){
    this.valueTitle = this.$refs.selectTree.getNode(this.valueId).data[this.props.label]   // 初始化显示
    this.$refs.selectTree.setCurrentKey(this.valueId)    // 设置默认选中
    this.defaultExpandedKey = [this.valueId]   // 设置默认展开
   } 
   this.$nextTick(()=>{
    let scrollWrap = document.querySelectorAll('.el-scrollbar .el-select-dropdown__wrap')[0]
    let scrollBar = document.querySelectorAll('.el-scrollbar .el-scrollbar__bar')
    scrollWrap.style.cssText = 'margin: 0px; max-height: none; overflow: hidden;'
    scrollBar.forEach(ele => ele.style.width = 0)
   })
 
  },
  // 切换选项
  handleNodeClick(node){
   this.valueTitle = node[this.props.label]
   this.valueId = node[this.props.value]
   this.$emit('getValue',this.valueId)
   this.defaultExpandedKey = []
  },
  // 清除选中
  clearHandle(){
   this.valueTitle = ''
   this.valueId = null
   this.defaultExpandedKey = []
   this.clearSelected()
   this.$emit('getValue',null)
  },
  /* 清空选中样式 */
  clearSelected(){
   let allNode = document.querySelectorAll('#tree-option .el-tree-node')
   allNode.forEach((element)=>element.classList.remove('is-current'))
  }
 },
 watch: {
  value(){
   this.valueId = this.value
   this.initHandle()
  }
 },
};
</script>

<style scoped>
 .el-scrollbar .el-scrollbar__view .el-select-dropdown__item{
  height: auto;
  max-height: 274px;
  padding: 0;
  overflow: hidden;
  overflow-y: auto;
 }
 .el-select-dropdown__item.selected{
  font-weight: normal;
 }
 ul li >.el-tree .el-tree-node__content{
  height:auto;
  padding: 0 20px;
 }
 .el-tree-node__label{
  font-weight: normal;
 }
 .el-tree >.is-current .el-tree-node__label{
  color: #409EFF;
  font-weight: 700;
 }
 .el-tree >.is-current .el-tree-node__children .el-tree-node__label{
  color:#606266;
  font-weight: normal;
 }
</style>