17：vue3 组件保持存活状态

<KeepAlive> 是一个内置组件，它的功能是在多个组件间动态切换时缓存被移除的组件实例

1、不使用KeepAlive，组件不保持存活，验证如下：

A组件

 1 <template>
 2     <h3>ComponentA</h3>
 3     <p>{{ message }}</p>
 4     <button @click="updateHandle">更新数据</button>
 5 </template>
 6 <script>
 7 export default{
 8     data(){
 9         return {
10             message:"老数据"
11         }
12     },
13     beforeUnmount(){
14         console.log("组件卸载之前");
15     },
16     unmounted(){
17         console.log("组件卸载之后");
18     },
19     methods: {
20         updateHandle(){
21             this.message="新数据"
22         }
23     }
24 }
25 </script>

B组件

1 <template>
2     <h3>ComponentB</h3>
3 </template>

App.vue

 1 <template>
 2   <h3>动态组件(A、B两个组件动态切换)</h3>
 3   <component :is="tabComponent"></component>
 4   <button @click="changeHandle">切换组件</button>
 5 </template>
 6 
 7 <script>
 8 import ComponentA from "./components/ComponentA.vue"
 9 import ComponentB from "./components/ComponentB.vue"
10 
11 export default{
12     data(){
13       return{
14         tabComponent:"ComponentA"
15       }
16     },
17     methods:{
18       changeHandle(){
19         this.tabComponent=this.tabComponent=="ComponentA"?"ComponentB":"ComponentA"
20       }
21    },
22    components:{
23     ComponentA,
24     ComponentB
25    }
26     
27 }
28 </script>