Vue中的keep-aliveinclude

一、什么是Vue中的keep-aliveinclude

Vue中的keep-aliveinclude是一个内置组件，它与Vue的动态组件结合使用可以将多个组件缓存起来，提高应用的性能和交互体验。

二、如何使用Vue中的keep-aliveinclude

使用Vue中的keep-aliveinclude需要先安装Vue，并在Vue实例中注册该组件。

Vue.component('keep-aliveinclude', {
  name: 'keep-aliveinclude',
  abstract: true,
  props: {
    include: patternTypes,
    exclude: patternTypes,
    max: [String, Number]
  },
  created: function created() {
    this.cache = Object.create(null);
    this.keys = [];
  },
  destroyed: function destroyed() {
    for (var key in this.cache) {
      pruneCacheEntry(this.cache, key, this.keys);
    }
  },
  mounted: function mounted() {
    var this$1 = this;
    this.$watch('include', function (val) {
      pruneCache(this$1, function (name) {
        return matches(val, name);
      });
    });
    this.$watch('exclude', function (val) {
      pruneCache(this$1, function (name) {
        return !matches(val, name);
      });
    });
  },
  render: function render() {
    var slot = this.$slots.default;
    var vnode = getFirstComponentChild(slot);
    var componentOptions = vnode && vnode.componentOptions;
    if (componentOptions) {
      // check pattern
      var name = getComponentName(componentOptions);
      var include = this.include;
      var exclude = this.exclude;
      if (
        // not included
        (include && (!name || !matches(include, name))) ||
        // excluded
        (exclude && name && matches(exclude, name))
      ) {
        return vnode;
      }
      var key =
        vnode.key == null
          // same constructor may get registered as different local components
          // so cid alone is not enough (#3269)
          ? componentOptions.Ctor.cid + (componentOptions.tag ? '::' + componentOptions.tag : '')
          : vnode.key;
      if (this.cache[key]) {
        vnode.componentInstance = this.cache[key].componentInstance;
        // make current key freshest
        remove(this.keys, key);
        this.keys.push(key);
      } else {
        this.cache[key] = vnode;
        this.keys.push(key);
        // prune oldest entry
        if (this.max && this.keys.length > parseInt(this.max)) {
          pruneCacheEntry(this.cache, this.keys[0], this.keys, this._vnode);
        }
      }
      vnode.data.keepAlive = true;
    }
    return vnode || (slot && slot[0]);
  }
})

在使用该组件时需要给include或exclude属性传递一个用来匹配要缓存的组件的字符串或正则表达式。

<keep-aliveinclude :include="'home|about|contact'">
  <router-view></router-view>
</keep-aliveinclude>

三、Vue中的keep-aliveinclude的优势

1. 减少组件的重复渲染

使用Vue中的keep-aliveinclude可以将多个组件缓存起来，避免在切换路由时重复渲染同一个组件。当再次访问该组件时，直接从缓存中获取组件，节省了重新渲染的时间。

2. 优化页面切换的性能

Vue中的keep-aliveinclude可以将多个组件缓存起来，当在多个组件之间切换时，保持之前组件的状态，不会销毁组件和组件实例，同时也不会销毁该组件相关的DOM元素，这样可以优化页面切换的性能，提升用户体验。

3. 控制缓存组件的数量

Vue中的keep-aliveinclude可以控制缓存组件的数量，避免占用过多的内存资源。

四、结语

Vue中的keep-aliveinclude是一个非常方便的组件，可以提高应用的性能和交互体验。在实际项目中，使用该组件可以有效地减少组件的重复渲染和优化页面切换的性能，提升用户体验。