<template>
  <div>
    <Sweiper v-model="selected">
      <!--v-model是个语法糖，相当于value和input事件-->
      <Sweiper-item  name="item1">
        <div class="item">
          <img :src="getImg('01')" alt="">
        </div>
      </Sweiper-item>
      <Sweiper-item name="item2">
        <div class="item">
          <img :src="getImg('02')" alt="">
        </div>
      </Sweiper-item>
      <Sweiper-item name="item3">
        <div class="item">
          <img :src="getImg('03')" alt="">
        </div>
      </Sweiper-item>
    </Sweiper>
  </div>
</template>
这里的图片没有通过数组用v-for循环，方便大家看其结构形式
<script>
  import Sweiper from "../components/Sweiper.vue";
  import SweiperItem from "../components/SweiperItem.vue";
  export default {
    name: "mySweiper",
    components: {
      Sweiper,
      SweiperItem
    },
    data() {
      return {
        selected: "item1",//默认第一张
      }
    },
    methods:{
      getImg(url){
        return "img/"+url+".jpg"
      },

    },
    mounted(){
      /*setInterval(()=>{
       this.selected="item2"
  },3000)
  此时因为mounted只执行一次，所以还是不变，需要在Sweiper写一个watch监听
    }*/这一步注释是因为换到Sweiper组件中写了
  }
</script>
<style >
  .item{
    /*border: 1px solid black;*/
  }
  .item>img{
    width: 100%;
    /*height: 0.1rem;*/
  }
</style>

<template>
  <div class="Sweiper">
    <slot></slot>
  </div>
</template>
<script>

  export default {
    name: "Sweiper",
    data() {
      return{
        current:''
      }
    },
    props:{
      value:{
        type:String,
        default:""
      },
    },
    mounted(){
      //自动轮播时查找name值用indexOf的方法遍历出当前轮播的下表
      this.names=this.$children.map(child=>{
       return child.name
      });
      this. showImg();
      this. paly()
    },
    methods:{
      showImg(){
        this.current=this.value||this.$children[0].name;
        //当前实例的直接子组件
        this.$children.map(vm=>{
          vm.selected=this.current
        })
      },

      paly(){
        //每次轮播把图片做调整
        this.timer=setInterval(()=>{
          //indexOf返回某个指定字符串首次出现的位置
          const index=this.names.indexOf(this.current);
          let newIndex=index+1;
          //严谨一点
          if (newIndex===this.names.length){
             newIndex=0;
          }
          this.$emit("input",this.names[newIndex])
        },3000)
      }
    },
    watch:{
      //监听value值，发生变化就改变selected
      value(){
        this. showImg()
      }
    },
    beforeDestroy() {
      //实列销毁前
      clearInterval(this.timer)
    }
  };
</script>
<style>
  .Sweiper{
    /*border: 1px solid black;*/
    width: 100%;
    height: 4rem;
    overflow: hidden;
    margin: 0 auto;
    position: relative;
  }
</style>

<template>
  <transition>
    <div class="Sweiper-item" v-show="isShow">
      <slot></slot>
    </div>
  </transition>
</template>
<script>
  export  default {
    name:"SweiperItem",
    data(){
      return{
        selected:""
      }
    },
    props:{
      name:{
        type:String,
        required:true
      },
    },
    mounted(){

    },
    computed:{
      isShow(){
        return this.selected===this.name;
      }
    }
  };

</script>
<style>
  .v-enter-active,.v-leave-active{
    transition: all 1s linear;
  }
  .v-leave-to{
    transform:translate(-100%);
  }
  .v-enter{
    transform: translate(100%);
  }
  .v-enter-active{
    position: absolute;
    top:0;
    left: 0;
  }
</style>