20180821 Vue父组件向子组件传递事件/调用事件

今天写Vue父组件向子组件传递事件/调用事件  的时候，

我怎么都不能成功。最后发先是  this.$refs.child 是个数组。 因为我这个子组件调用了多次

---

父组件app.vue

<template>
      <div id="app">
        <!--父组件-->
        <input v-model="msg">
        <button v-on:click="notify">广播事件</button>
        <!--子组件-->
        <popup ref="child" ></popup>
      </div>
    </template>
    <script>
      import popup from '@/components/popup'
      export default {
        name: 'app',
        data: function () {
          return {
            msg: ''
          }
        },
        components: {
          popup
        },
        methods: {
          notify: function () {
            if (this.msg.trim()) {
              this.$refs.child.parentMsg(this.msg)
            }
          }
        }
      }
    </script>
    <style>
      #app {
        font-family: 'Avenir', Helvetica, Arial, sans-serif;
        -webkit-font-smoothing: antialiased;
        -moz-osx-font-smoothing: grayscale;
        text-align: center;
        color: #2c3e50;
        margin-top: 60px;
      }
    </style>

　　子组件popup.vue

     <template>
         <div>
           <ul>
             <li v-for="item in messages">父组件输入了：{{item}}</li>
           </ul>
         </div>
     </template>
     <style>
         body {
             background-color: #ffffff;
         }
     </style>
     <script>
       export default{
         name: 'popup',
         data: function () {
           return {
             messages: []
           }
         },
         methods: {
           parentMsg: function (msg) {
             this.messages.push(msg)
           }
         }
       }
     </script>