vue中的keep-alive用法指南

<template>
  <keep-alive>
    <component :is="view"></component>
  </keep-alive>
</template>
<script>
export default {
  data() {
    return {
      view: 'homeComponent'
    };
  }
};
</script>

<keep-alive include="ComponentA, ComponentB" exclude="ComponentC">
  <router-view></router-view>
</keep-alive>

<keep-alive :max="6">
  <router-view></router-view>
</keep-alive>

export default {
  activated() {
    console.log('组件被激活了');
  },
  deactivated() {
    console.log('组件被缓存了');
  }
};

export default {
  name: 'KeepAlive',
  abstract: true, // 这是一个抽象组件，表示它不会直接渲染到 DOM 上
  props: {
    include: patternTypes, // 要缓存的组件
    exclude: patternTypes, // 不缓存的组件
    max: [String, Number] // 最大缓存数
  },
  created () {
    this.cache = Object.create(null); // 缓存对象
    this.keys = []; // 用来记录缓存的顺序
  },
  destroyed () {
    for (const key in this.cache) {
      pruneCacheEntry(this.cache, key, this.keys);
    }
  },
  watch: {
    include (val) {
      pruneCache(this, name => matches(val, name));
    },
    exclude (val) {
      pruneCache(this, name => !matches(val, name));
    }
  },
  render () {
    const slot = this.$slots.default;
    const vnode = getFirstComponentChild(slot); // 获取第一个子组件
    if (vnode) {
      const componentOptions = vnode.componentOptions;
      const name = getComponentName(componentOptions);
      if (name && (
        (this.include && !matches(this.include, name)) ||
        (this.exclude && matches(this.exclude, name))
      )) {
        return vnode; // 如果不匹配 include/exclude，直接返回，不缓存
      }
      const key = vnode.key == null
        ? componentOptions.Ctor.cid + (componentOptions.tag ? `::${componentOptions.tag}` : '')
        : vnode.key;
      if (this.cache[key]) {
        vnode.componentInstance = this.cache[key].componentInstance; // 从缓存中取出实例
        remove(this.keys, key); // 移除旧的位置
        this.keys.push(key); // 重新放到最后，更新 LRU 位置
      } else {
        this.cache[key] = vnode; // 缓存新实例
        this.keys.push(key);
        // 如果超过最大缓存数，移除最早的实例
        if (this.max && this.keys.length > parseInt(this.max)) {
          pruneCacheEntry(this.cache, this.keys[0], this.keys, this._vnode);
        }
      }
      vnode.data.keepAlive = true; // 标记组件为 keep-alive
    }
    return vnode || (slot && slot[0]); // 返回 vnode
  }
};