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vue3使用keep-alive组件，包含动态组件使用

组件不使用keep-alive

• Father

<template>
  <div>
    Father
    <el-button @click="tabChange">change page</el-button>
    <Child :msg="cutTab" v-if="cutTab"></Child>
    <Child2 :msg="cutTab" v-else></Child2>
  </div>
</template>

<script setup lang="ts" name="Father">
const cutTab = ref(false);

const tabChange = () => {
  cutTab.value = !cutTab.value;
}
</script>

• Child

<template>
  <div class="c1">
    Child +
    {{ props.msg }}
    <el-input v-model="input" placeholder="Please input" />
  </div>
</template>

<script setup lang="ts" name="Child">
const props = defineProps({
  msg: {
    type: Boolean,
    default: false,
  },
})
const input = ref('')
</script>

• Child2

<template>
  <div class="c2">
    Child2 +
    {{ props.msg }}
    <el-input v-model="input" placeholder="Please input" />
  </div>
</template>

<script setup lang="ts" name="Child2">
const props = defineProps({
  msg: {
    type: Boolean,
    default: false,
  },
})
const input = ref('')
</script>

组件中使用

• include：包含
• exclude：排除

v-if切换

    <keep-alive>
      <Child :msg="cutTab" v-if="cutTab"></Child>
      <Child2 :msg="cutTab" v-else></Child2>
    </keep-alive>

    <keep-alive include="Child2">
      <Child :msg="cutTab" v-if="cutTab"></Child>
      <Child2 :msg="cutTab" v-else></Child2>
    </keep-alive>

component动态组件切换

因注释导致的意外错误

• <KeepAlive> expects exactly one child component
  

    <keep-alive include="Child2">
      <!-- <Child :msg="cutTab" v-if="cutTab"></Child>
      <Child2 :msg="cutTab" v-else></Child2> -->
      <component :is="com"></component>
    </keep-alive>

keep-alive组件内不要使用注释，会被解析为子节点

• 添加div进行包裹

    <keep-alive include="Child2">
      <div>
        <!-- <Child :msg="cutTab" v-if="cutTab"></Child>
        <Child2 :msg="cutTab" v-else></Child2> -->
        <component :is="com"></component>s
      </div>
    </keep-alive>

• 移除注释

    <keep-alive include="Child2">
      <component :is="com"></component>
    </keep-alive>

动态组件的使用

[Vue warn]: Vue received a Component which was made a reactive object. This can lead to unnecessary performance overhead, and should be avoided by marking the component with 'markRaw' or using 'shallowRef' instead of 'ref'.

在 Vue 3 中，如果用 ref 或 reactive 将一个组件包装成响应式对象，可能会引发不必要的性能开销。因为这会使 Vue 尝试去追踪组件的变化，而实际上组件实例并不需要被追踪。组件本身不应该是响应式的，只有它的 props 和 state 才应该是响应式的。

所以，当需要引用一个组件时，应该使用 shallowRef或者 markRaw，这样可以避免将整个组件变成响应式的，只会跟踪引用的变化

• 使用markRaw

const com = ref(markRaw(Child2));

const comChange = () => {
  if(com.value === Child2){
    com.value = markRaw(Child);
  }else{
    com.value = markRaw(Child2);
  }
}

• 使用shallowRef

const com = shallowRef(Child2);

const comChange = () => {
  if(com.value === Child2){
    com.value = Child;
  }else{
    com.value = Child2;
  }
}

完整示例

<template>
  <div>
    Father
    <el-button @click="comChange">change component</el-button>
    <keep-alive include="Child2">
      <component :is="com"></component>
    </keep-alive>
  </div>
</template>

<script setup lang="ts" name="Father">
import Child from "@/views/Child.vue";
import Child2 from "@/views/Child2.vue";

const cutTab = ref(false);
const com = ref(markRaw(Child2));

const comChange = () => {
  if(com.value === Child2){
    com.value = markRaw(Child);
  }else{
    com.value = markRaw(Child2);
  }
}

</script>

可以看到只有Child2组件是有缓存的，Child是有销毁和生成的

路由不使用keep-alive

• 组件

<template>
  <div>
    Father
    <div class="nav">
      <router-link to="/Father/Child">去Child页面</router-link>
      <el-divider direction="vertical" />
      <router-link to="/Father/Child2">去Child2页面</router-link>
    </div>
    <router-view></router-view>
  </div>
</template>

• 路由index.ts

import { createRouter, createWebHashHistory, createWebHistory } from 'vue-router'
import Home from '@/views/Home.vue'

const routes = [
  {
    path: '/Father',
    name: 'Father',
    component: () => import('@/views/Father.vue'),
    children: [
      {
        path: 'Child',
        name: 'Child',
        component: () => import('@/views/Child.vue'),
      },
      {
        path: 'Child2',
        name: 'Child2',
        component: () => import('@/views/Child2.vue'),
      }
    ],
  }, 
]

const router = createRouter({
  history: createWebHashHistory(),
  routes
})

export default router

路由中使用

• Vue Router 4（与 Vue 3 配套的路由库）引入了一个新的 API 来实现路由级别的 <keep-alive>。这就是 <router-view> 组件的 v-slot API

  • 需要注意的是v-if不要加在keep-alive上，会直接销毁keep-alive，需要加在component上
  • 实现页面部分刷新，页面进入时执行的生命周期为：created->mounted->activated

<template>
  <div>
    Father
    <div class="nav">
      <router-link to="/Father/Child">去Child页面</router-link>
      <el-divider direction="vertical" />
      <router-link to="/Father/Child2">去Child2页面</router-link>
    </div>
    <router-view v-slot="{ Component }">
      <keep-alive >
        <component :is="Component" v-if="$route.meta.keepAlive"/>
      </keep-alive>
      <component :is="Component" v-if="!$route.meta.keepAlive"/>
    </router-view>
  </div>
</template>

• 路由index.ts

  • 在对应的路由上添加meta属性来设置页面是否要使用缓存

...
const routes = [
  {
    path: '/Father',
    name: 'Father',
    component: () => import('@/views/Father.vue'),
    children: [
      {
        path: 'Child',
        name: 'Child',
        component: () => import('@/views/Child.vue'),
      },
      {
        path: 'Child2',
        name: 'Child2',
        meta: {
          keepAlive: true,  // 需要被keep-alive
        },
        component: () => import('@/views/Child2.vue'),
      }
    ],
  }, 
]
...

keep-alive生命周期

有keep-alive组件会多出两个生命周期，分别在mounted之后和unMounted之前

onActivated(() => {
  console.log('Component is activated')
})

onDeactivated(() => {
  console.log('Component is deactivated')
})