1. 作用: 让不展示的路由组件保持挂载,不被销毁.
2. 具体代码
2.1 缓存展示区所有组件
<keep-alive>
<router-view><router-view>
</keep-alive>
2.2 缓存一个组件
<keep-alive include='组件名'>
<router-view><router-view>
</keep-alive>
2.3 缓存多个组件
<keep-alive :include="['组件名1','组件名2']">
<router-view><router-view>
</keep-alive>
