子组件：foods

<div id='app'>

    <div class="box" v-show="showFlag">11111111111111</div>
</div>

<script>

export default({

data(){return{showFlag:false}},

methods:{
    show(){
      this.showFlag = true
    }
}

})

</script>

父组件：parent.vue

<div class="parents">

    <Foods ref='foods'></Foods>

    <button @click='btn'>我是父组件</button>
</div>

<script>

import Foods from 'foods'
   export default {
     methods:{
        btn(){
           this.$refs.foods.show()
         }
     },

   components:{

    Foods      

    }
   }
</script>