How to expand all collapse panels

Method ： The default expansion value of the folding panel is activeNames, Just traverse all el-collapse-iteme, Put it name Value is inserted into the
activeNames Then you can .

<template>
  <div>
    <el-collapse v-model="activeNames">
      <div v-for="(item,index) in moduleFiles">
      <el-collapse-item :title="item.totle" :name="index">
        <div>{
    {
    item.content}}</div>
      </el-collapse-item>
     </div> 
    </el-collapse>
  </div>
</template>
 data() {
    
      return {
    
        moduleFiles:[
          {
    title:" study hard ",content:" Reading is not just about strengthening yourself , And for the rise of China "},
          {
    title:" study hard ",content:" Reading is not just about strengthening yourself , And for the rise of China "},
          {
    title:" study hard ",content:" Reading is not just about strengthening yourself , And for the rise of China "},
          {
    title:" study hard ",content:" Reading is not just about strengthening yourself , And for the rise of China "},
        ],
        activeNames:[],
     }
    },
mounted(){
    
 const open =[];
      for(let i=0;i<this.moduleFiles.length;i++){
    
        open.push(i);
      }
      this.activeNames = open;
}

give the result as follows ：