- 1、通過本文可以瞭解到vue3 keepalive功能
- 2、通過本文可以瞭解到vue3 keepalive使用場景
- 3、通過本文可以學習到vue3 keepalive真實的使用過程
- 4、通過本文可以學習vue3 keepalive原始碼除錯
- 5、通過本文可以學習到vue3 keepalive原始碼的精簡分析
1、keepalive功能
- keepalive是vue3中的一個全域性元件
- keepalive 本身不會渲染出來,也不會出現在dom節點當中,但是它會被渲染為vnode,通過vnode可以跟蹤到keepalive中的cache和keys,當然也是在開發環境才可以,build打包以後沒有暴露到vnode中(這個還要再確認一下)
- keepalive 最重要的功能就是快取元件
- keepalive 通過LRU快取淘汰策略來更新元件快取,可以更有效的利用記憶體,防止記憶體溢位,原始碼中的最大快取數max為10,也就是10個元件之後,就開始淘汰最先被快取的元件了
2、keepalive使用場景
- 這裡先假設一個場景: A頁面是首頁=> B頁面列表頁面(需要快取的頁面)===> C 詳情頁
由C詳情頁到到B頁面的時候,要返回到B的快取頁面,包括頁面的基礎資料和列表的滾動條位置資訊
如果由B頁面返回到A頁面,則需要將B的快取頁清空 - 上述另外一個場景:進入頁面直接快取,然後就結束了,這個比較簡單本文就不討論了
3、在專案中的使用過程
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keepalive元件總共有三個引數
- include:可傳字串、正規表示式、陣列,名稱匹配成功的元件會被快取
- exclude:可傳字串、正規表示式、陣列,名稱匹配成功的元件不會被快取
- max:可傳數字,限制快取元件的最大數量,預設為10
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首先在App.vue根程式碼中新增引入keepalive元件,通過這裡可以發現,我這裡快取的相當於整個頁面,當然你也可以進行更細粒度的控制頁面當中的某個區域元件
<template> <router-view v-slot="{ Component }"> <keep-alive :include="keepAliveCache"> <component :is="Component" :key="$route.name" /> </keep-alive> </router-view> </template> <script lang="ts" setup> import { computed } from "vue"; import { useKeepAliverStore } from "@/store"; const useStore = useKeepAliverStore(); const keepAliveCache = computed(() => { return useStore.caches; }); </script>
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通過App.vue可以發現,通過pinia(也就是vue2中使用的vuex)儲存要快取的頁面元件, 來處理include快取,和儲存頁面元件中的滾動條資訊資料
import { defineStore } from "pinia"; export const useKeepAliverStore = defineStore("useKeepAliverStore", { state: () => ({ caches: [] as any, scrollList: new Map(), // 快取頁面元件如果又滾動條的高度 }), actions: { add(name: string) { this.caches.push(name); }, remove(name: string) { console.log(this.caches, 'this.caches') this.caches = this.caches.filter((item: any) => item !== name); console.log(this.caches, 'this.caches') }, clear() { this.caches = [] } } });
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元件路由剛剛切換時,通過beforeRouteEnter將元件寫入include, 此時元件生命週期還沒開始。如果都已經開始執行元件生命週期了,再寫入就意義了。所以這個鉤子函式就不能寫在setup中,要單獨提出來寫。當然你也可以換成路由的其他鉤子函式處理beforeEach,但這裡面使用的話,好像使用不了pinia,這個還需要進一步研究一下。
import { useRoute, useRouter, onBeforeRouteLeave } from "vue-router"; import { useKeepAliverStore } from "@/store"; const useStore = useKeepAliverStore() export default { name:"record-month", beforeRouteEnter(to, from, next) { next(vm => { if(from.name === 'Home' && to.name === 'record-month') { useStore.add(to.name) } }); } } </script>
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元件路由離開時判斷,是否要移出快取,這個鉤子就直接寫在setup中就可以了。
onBeforeRouteLeave((to, from) => { console.log(to.name, "onBeforeRouteLeave"); if (to.name === "new-detection-detail") { console.log(to, from, "進入詳情頁面不做處理"); } else { useStore.remove(from.name) console.log(to, from, "刪除元件快取"); } });
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在keepalive兩個鉤子函式中進行處理scroll位置的快取,onActivated中獲取快取中的位置, onDeactivated記錄位置到快取
onActivated(() => { if(useStore.scrollList.get(routeName)) { const top = useStore.scrollList.get(routeName) refList.value.setScrollTop(Number(top)) } }); onDeactivated(() => { const top = refList.value.getScrollTop() useStore.scrollList.set(routeName, top) });
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這裡定義一個方法,設定scrollTop使用了原生javascript的api
const setScrollTop = (value: any) => { const dom = document.querySelector('.van-pull-refresh') dom!.scrollTop = value }
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同時高度怎麼獲取要先註冊scroll事件,然後通過getScrollTop 獲取當前滾動條的位置進行儲存即可
onMounted(() => { scrollDom.value = document.querySelector('.van-pull-refresh') as HTMLElement const throttledFun = useThrottleFn(() => { console.log(scrollDom.value?.scrollTop, 'addEventListener') state.scrollTop = scrollDom.value!.scrollTop }, 500) if(scrollDom.value) { scrollDom.value.addEventListener('scroll',throttledFun) } }) const getScrollTop = () => { console.log('scrollDom.vaue', scrollDom.value?.scrollTop) return state.scrollTop }
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上面註冊scroll事件中使用了一個useThrottleFn,這個類庫是@vueuse/core中提供的,其中封裝了很多工具都非常不錯,用興趣的可以研究研究
https://vueuse.org/shared/usethrottlefn/#usethrottlefn
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此時也可以檢視找到例項的vnode查詢到keepalive,是在keepalive緊挨著的子元件裡
const instance = getCurrentInstance() console.log(instance.vnode.parent) // 這裡便是keepalive元件vnode // 如果是在開發環境中可以檢視到cache物件 instance.vnode.parent.__v_cache // vue原始碼中,在dev環境對cache進行暴露,生產環境是看不到的 if (__DEV__ || __FEATURE_PROD_DEVTOOLS__) { ;(instance as any).__v_cache = cache }
4、vue3 keepalive原始碼除錯
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1、克隆程式碼
git clone git@github.com:vuejs/core.git
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2、安裝依賴
pnpm i
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3、如果不能使用pnpm,可以先通過npm安裝一下
npm i pnpm -g
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4、安裝完成以後,找到根目錄package.json檔案中的scripts
- 參考https://juejin.cn/post/6991653445161713671
// 在dev命令後新增 --source-map是從已轉換的程式碼,對映到原始的原始檔 "dev": "node scripts/dev.js --sourcemap"
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5、執行pnpm run dev則會build vue原始碼
pnpm run dev //則會出現以下,代表成功了(2022年5月27日),後期vue原始碼作者可能會更新,相應的提示可能發生變更,請注意一下 > @3.2.36 dev H:\github\sourceCode\core > node scripts/dev.js --sourcemap watching: packages\vue\dist\vue.global.js //到..\..\core\packages\vue\dist便可以看到編譯成功,以及可以檢視到examples樣例demo頁面
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6、然後在 ....\core\packages\vue\examples\composition中新增一個aehyok.html檔案,將如下程式碼進行拷貝,然後通過chrome瀏覽器開啟,F12,找到原始碼的Tab頁面,通過快捷鍵Ctrl+ P 輸入KeepAlive便可以找到這個元件,然後通過左側行標右鍵就可以新增斷點,進行除錯,也可以通過右側的【呼叫堆疊】進行快速跳轉程式碼進行除錯。
<script src="../../dist/vue.global.js"></script> <script type="text/x-template" id="template-1"> <div>template-1</div> <div>template-1</div> </script> <script type="text/x-template" id="template-2"> <div>template-2</div> <div>template-2</div> </script> <script> const { reactive, computed } = Vue const Demo1 = { name: 'Demo1', template: '#template-1', setup(props) { } } const Demo2 = { name: 'Demo2', template: '#template-2', setup(props) { } } </script> <!-- App template (in DOM) --> <div id="demo"> <div>Hello World</div> <div>Hello World</div> <div>Hello World</div> <button @click="changeClick(1)">元件一</button> <button @click="changeClick(2)">元件二</button> <keep-alive :include="includeCache"> <component :is="componentCache" :key="componentName" v-if="componentName" /> </keep-alive> </div> <!-- App script --> <script> Vue.createApp({ components: { Demo1, Demo2 }, data: () => ({ includeCache: [], componentCache: '', componentName: '', }), methods:{ changeClick(type) { if(type === 1) { if(!this.includeCache.includes('Demo1')) { this.includeCache.push('Demo1') } console.log(this.includeCache, '000') this.componentCache = Demo1 this.componentName = 'Demo1' } if(type === 2) { if(!this.includeCache.includes('Demo2')) { this.includeCache.push('Demo2') } console.log(this.includeCache, '2222') this.componentName = 'Demo2' this.componentCache = Demo2 } } } }).mount('#demo') </script>
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7、除錯原始碼發現 keepalive中的render函式(或者說時setup中的return 函式)在子元件切換時就會去執行,變更邏輯快取
- 第一次進入頁面初始化keepalive元件會執行一次,
- 然後點選元件一,再次執行render函式
- 然後點選元件二,會再次執行render函式
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8、除錯截圖說明
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9、除錯操作,小視訊觀看
5、vue3 keealive原始碼粗淺分析
- 通過檢視vue3 KeepAlive.ts原始碼,原始碼路徑:https://github.com/vuejs/core/blob/main/packages/runtime-core/src/components/KeepAlive.ts
// 在setup初始化中,先獲取keepalive例項 // getCurrentInstance() 可以獲取當前元件的例項 const instance = getCurrentInstance()! // KeepAlive communicates with the instantiated renderer via the // ctx where the renderer passes in its internals, // and the KeepAlive instance exposes activate/deactivate implementations. // The whole point of this is to avoid importing KeepAlive directly in the // renderer to facilitate tree-shaking. const sharedContext = instance.ctx as KeepAliveContext // if the internal renderer is not registered, it indicates that this is server-side rendering, // for KeepAlive, we just need to render its children /// SSR 判斷,暫時可以忽略掉即可。 if (__SSR__ && !sharedContext.renderer) { return () => { const children = slots.default && slots.default() return children && children.length === 1 ? children[0] : children } } // 通過Map儲存快取vnode, // 通過Set儲存快取的key(在外面設定的key,或者vnode的type) const cache: Cache = new Map() const keys: Keys = new Set() let current: VNode | null = null if (__DEV__ || __FEATURE_PROD_DEVTOOLS__) { ;(instance as any).__v_cache = cache } const parentSuspense = instance.suspense const { renderer: { p: patch, m: move, um: _unmount, o: { createElement } } } = sharedContext // 建立了隱藏容器 const storageContainer = createElement('div') // 在例項上註冊兩個鉤子函式 activate, deactivate sharedContext.activate = (vnode, container, anchor, isSVG, optimized) => { const instance = vnode.component! move(vnode, container, anchor, MoveType.ENTER, parentSuspense) // in case props have changed patch( instance.vnode, vnode, container, anchor, instance, parentSuspense, isSVG, vnode.slotScopeIds, optimized ) queuePostRenderEffect(() => { instance.isDeactivated = false if (instance.a) { invokeArrayFns(instance.a) } const vnodeHook = vnode.props && vnode.props.onVnodeMounted if (vnodeHook) { invokeVNodeHook(vnodeHook, instance.parent, vnode) } }, parentSuspense) if (__DEV__ || __FEATURE_PROD_DEVTOOLS__) { // Update components tree devtoolsComponentAdded(instance) } } sharedContext.deactivate = (vnode: VNode) => { const instance = vnode.component! move(vnode, storageContainer, null, MoveType.LEAVE, parentSuspense) queuePostRenderEffect(() => { if (instance.da) { invokeArrayFns(instance.da) } const vnodeHook = vnode.props && vnode.props.onVnodeUnmounted if (vnodeHook) { invokeVNodeHook(vnodeHook, instance.parent, vnode) } instance.isDeactivated = true }, parentSuspense) if (__DEV__ || __FEATURE_PROD_DEVTOOLS__) { // Update components tree devtoolsComponentAdded(instance) } } // 元件解除安裝 function unmount(vnode: VNode) { // reset the shapeFlag so it can be properly unmounted resetShapeFlag(vnode) _unmount(vnode, instance, parentSuspense, true) } // 定義 include和exclude變化時,對快取進行動態處理 function pruneCache(filter?: (name: string) => boolean) { cache.forEach((vnode, key) => { const name = getComponentName(vnode.type as ConcreteComponent) if (name && (!filter || !filter(name))) { pruneCacheEntry(key) } }) } function pruneCacheEntry(key: CacheKey) { const cached = cache.get(key) as VNode if (!current || cached.type !== current.type) { unmount(cached) } else if (current) { // current active instance should no longer be kept-alive. // we can't unmount it now but it might be later, so reset its flag now. resetShapeFlag(current) } cache.delete(key) keys.delete(key) } // 可以發現通過include 可以配置被顯示的元件, // 當然也可以設定exclude來配置不被顯示的元件, // 元件切換時隨時控制快取 watch( () => [props.include, props.exclude], ([include, exclude]) => { include && pruneCache(name => matches(include, name)) exclude && pruneCache(name => !matches(exclude, name)) }, // prune post-render after `current` has been updated { flush: 'post', deep: true } ) // 定義當前元件Key // cache sub tree after render let pendingCacheKey: CacheKey | null = null // 這是一個重要的方法,設定快取 const cacheSubtree = () => { // fix #1621, the pendingCacheKey could be 0 if (pendingCacheKey != null) { cache.set(pendingCacheKey, getInnerChild(instance.subTree)) } } onMounted(cacheSubtree) onUpdated(cacheSubtree) // 元件解除安裝的時候,對快取列表進行迴圈判斷處理 onBeforeUnmount(() => { cache.forEach(cached => { const { subTree, suspense } = instance const vnode = getInnerChild(subTree) if (cached.type === vnode.type) { // current instance will be unmounted as part of keep-alive's unmount resetShapeFlag(vnode) // but invoke its deactivated hook here const da = vnode.component!.da da && queuePostRenderEffect(da, suspense) return } unmount(cached) }) }) // 同時在keepAlive元件setup生命週期中,return () => {} 渲染的時候,對元件進行判斷邏輯處理,同樣對include和exclude判斷渲染。 // 判斷keepalive元件中的子元件,如果大於1個的話,直接警告處理了 // 另外如果渲染的不是虛擬dom(vNode),則直接返回渲染即可。 return () => { // eslint-disable-next-line no-debugger console.log(props.include, 'watch-include') pendingCacheKey = null if (!slots.default) { return null } const children = slots.default() const rawVNode = children[0] if (children.length > 1) { if (__DEV__) { warn(`KeepAlive should contain exactly one component child.`) } current = null return children } else if ( !isVNode(rawVNode) || (!(rawVNode.shapeFlag & ShapeFlags.STATEFUL_COMPONENT) && !(rawVNode.shapeFlag & ShapeFlags.SUSPENSE)) ) { current = null return rawVNode } // 接下來處理時Vnode虛擬dom的情況,先獲取vnode let vnode = getInnerChild(rawVNode) // 節點型別 const comp = vnode.type as ConcreteComponent // for async components, name check should be based in its loaded // inner component if available // 獲取元件名稱 const name = getComponentName( isAsyncWrapper(vnode) ? (vnode.type as ComponentOptions).__asyncResolved || {} : comp ) //這個算是最熟悉的通過props傳遞進行的引數,進行解構 const { include, exclude, max } = props // include判斷 元件名稱如果沒有設定, 或者元件名稱不在include中, // exclude判斷 元件名稱有了,或者匹配了 // 對以上兩種情況都不進行快取處理,直接返回當前vnode虛擬dom即可。 if ( (include && (!name || !matches(include, name))) || (exclude && name && matches(exclude, name)) ) { current = vnode return rawVNode } // 接下來開始處理有快取或者要快取的了 // 先獲取一下vnode的key設定,然後看看cache快取中是否存在 const key = vnode.key == null ? comp : vnode.key const cachedVNode = cache.get(key) // 這一段可以忽略了,好像時ssContent相關,暫時不管了,沒看明白?? // clone vnode if it's reused because we are going to mutate it if (vnode.el) { vnode = cloneVNode(vnode) if (rawVNode.shapeFlag & ShapeFlags.SUSPENSE) { rawVNode.ssContent = vnode } } // 上面判斷了,如果沒有設定key,則使用vNode的type作為key值 pendingCacheKey = key //判斷上面快取中是否存在vNode // if 存在的話,就將快取中的vnode複製給當前的vnode // 同時還判斷了元件是否為過渡元件 transition,如果是的話 需要註冊過渡元件的鉤子 // 同時先刪除key,然後再重新新增key // else 不存在的話,就新增到快取即可 // 並且要判斷一下max最大快取的數量是否超過了,超過了,則通過淘汰LPR演算法,刪除最舊的一個快取 // 最後又判斷了一下是否為Suspense。也是vue3新增的高階元件。 if (cachedVNode) { // copy over mounted state vnode.el = cachedVNode.el vnode.component = cachedVNode.component if (vnode.transition) { // recursively update transition hooks on subTree setTransitionHooks(vnode, vnode.transition!) } // avoid vnode being mounted as fresh vnode.shapeFlag |= ShapeFlags.COMPONENT_KEPT_ALIVE // make this key the freshest keys.delete(key) keys.add(key) } else { keys.add(key) // prune oldest entry if (max && keys.size > parseInt(max as string, 10)) { pruneCacheEntry(keys.values().next().value) } } // avoid vnode being unmounted vnode.shapeFlag |= ShapeFlags.COMPONENT_SHOULD_KEEP_ALIVE current = vnode return isSuspense(rawVNode.type) ? rawVNode : vnode
6、總結
通過這次檢視vue3 keepalive原始碼發現,其實也沒那麼難,當然這次檢視原始碼也只是粗略檢視,並沒有看的那麼細,主要還是先解決問題。動動手除錯一下,有時候真的就是不逼一下自己都不知道自己有多麼的優秀。原來我也能稍微看看原始碼了。以後有空可以多看看vue3原始碼,學習一下vue3的精髓。瞭解vue3更為細節的一些知識點。
https://github.com/aehyok/vue-qiankun
本文涉及到的程式碼後續會整理到該程式碼倉庫中
https://github.com/aehyok/2022
最後自己每天工作中的筆記記錄倉庫,主要以文章連結和問題處理方案為主。