Vue动态组件

前面的话

　　让多个组件使用同一个挂载点，并动态切换，这就是动态组件。本文将详细介绍Vue动态组件

概述

　　通过使用保留的 <component> 元素，动态地绑定到它的 is 特性，可以实现动态组件

<div id="example">
  <button @click="change">切换页面</button>
  <component :is="currentView"></component>
</div>

<script>
var home = {template:'<div>我是主页</div>'};
var post = {template:'<div>我是提交页</div>'};
var archive = {template:'<div>我是存档页</div>'};
new Vue({
  el: '#example',
  components: {
    home,
    post,
    archive,
  },
  data:{
    index:0,
    arr:['home','post','archive'],
  },
  computed:{
    currentView(){
        return this.arr[this.index];
    }
  },
  methods:{
    change(){
      this.index = (++this.index)%3;
    }
  }
})
</script>

　　也可以直接绑定到组件对象上

<div id="example">
  <button @click="change">切换页面</button>
  <component :is="currentView"></component>
</div>

<script>
new Vue({
  el: '#example',
  data:{
    index:0,
    arr:[
      {template:`<div>我是主页</div>`},
      {template:`<div>我是提交页</div>`},
      {template:`<div>我是存档页</div>`}
    ],
  },
  computed:{
    currentView(){
        return this.arr[this.index];
    }
  },
  methods:{
    change(){
      this.index = (++this.index)%3;
    }
  }
})
</script>

缓存

　　<keep-alive> 包裹动态组件时，会缓存不活动的组件实例，而不是销毁它们。和 <transition> 相似，<keep-alive> 是一个抽象组件：它自身不会渲染一个 DOM 元素，也不会出现在父组件链中

【基础用法】

<div id="example">
  <button @click="change">切换页面</button>
  <keep-alive>
    <component :is="currentView"></component>  
  </keep-alive>
</div>

<script>
new Vue({
  el: '#example',
  data:{
    index:0,
    arr:[
      {template:`<div>我是主页</div>`},
      {template:`<div>我是提交页</div>`},
      {template:`<div>我是存档页</div>`}
    ],
  },
  computed:{
    currentView(){
        return this.arr[this.index];
    }
  },
  methods:{
    change(){
      let len = this.arr.length;
      this.index = (++this.index)% len;
    }
  }
})
</script>

【条件判断】

　　如果有多个条件性的子元素，<keep-alive> 要求同时只有一个子元素被渲染

<div id="example">
  <button @click="change">切换页面</button>
  <keep-alive>
    <home v-if="index===0"></home>
    <posts v-else-if="index===1"></posts>
    <archive v-else></archive>  
  </keep-alive>
</div>

<script>
new Vue({
  el: '#example',
  components:{
    home:{template:`<div>我是主页</div>`},
    posts:{template:`<div>我是提交页</div>`},
    archive:{template:`<div>我是存档页</div>`},
  },
  data:{
    index:0,
  },
  methods:{
    change(){
      let len = Object.keys(this.$options.components).length;
      this.index = (++this.index)%len;
    }
  }
})
</script>

【activated 和 deactivated】 

　　activated 和 deactivated 在 <keep-alive> 树内的所有嵌套组件中触发

<div id="example">
  <button @click="change">切换页面</button>
  <keep-alive>
    <component :is="currentView" @pass-data="getData"></component> 
  </keep-alive>
  <p>{{msg}}</p>
</div>

<script>
new Vue({
  el: '#example',
  data:{
    index:0,
    msg:'',    
    arr:[
      { 
        template:`<div>我是主页</div>`,
        activated(){
          this.$emit('pass-data','主页被添加');
        },
        deactivated(){
          this.$emit('pass-data','主页被移除');
        },        
      },
      {template:`<div>我是提交页</div>`},
      {template:`<div>我是存档页</div>`}
    ],
  },
  computed:{
    currentView(){
        return this.arr[this.index];
    }
  },
  methods:{
    change(){
      var len = this.arr.length;
      this.index = (++this.index)% len;
    },
    getData(value){
      this.msg = value;
      setTimeout(()=>{
        this.msg = '';
      },500)
    }
  }
})
</script>

【include和exclude】

　　include 和 exclude 属性允许组件有条件地缓存。二者都可以用逗号分隔字符串、正则表达式或一个数组来表示

<!-- 逗号分隔字符串 -->
<keep-alive include="a,b">
  <component :is="view"></component>
</keep-alive>
<!-- 正则表达式 (使用 v-bind) -->
<keep-alive :include="/a|b/">
  <component :is="view"></component>
</keep-alive>
<!-- Array (use v-bind) -->
<keep-alive :include="['a', 'b']">
  <component :is="view"></component>
</keep-alive>

　　匹配首先检查组件自身的 name 选项，如果 name 选项不可用，则匹配它的局部注册名称（父组件 components 选项的键值）。匿名组件不能被匹配

  <keep-alive include="home,archive">
    <component :is="currentView"></component> 
  </keep-alive>

　　上面的代码，表示只缓存home和archive，不缓存posts

<div id="example">
  <button @click="change">切换页面</button>
  <keep-alive include="home,archive">
    <component :is="currentView"></component> 
  </keep-alive>
</div>
<script src="https://unpkg.com/vue"></script>
<script>
new Vue({
  el: '#example',
  data:{
    index:0,   
    arr:[
      {name:'home',template:`<div>我是主页</div>`},
      {name:'posts',template:`<div>我是提交页</div>`},
      {name:'archive',template:`<div>我是存档页</div>`}
    ],
  },
  computed:{
    currentView(){
        return this.arr[this.index];
    }
  },
  methods:{
    change(){
      var len = this.arr.length;
      this.index = (++this.index)% len;
    },
  }
})
</script>