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<!DOCTYPE HTML> <html lang="zh-cn" > <head> <meta charset="UTF-8"> <meta content="text/html; charset=utf-8" http-equiv="Content-Type"> <title>Action · Vuex</title> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta name="description" content=""> <meta name="generator" content="GitBook 3.2.3"> <link rel="stylesheet" href="../gitbook/style.css"> <link rel="stylesheet" href="../gitbook/gitbook-plugin-prism/prism.css"> <link rel="stylesheet" href="../gitbook/gitbook-plugin-search/search.css"> <link rel="stylesheet" href="../gitbook/gitbook-plugin-theme-vuejs/vue.css"> <meta name="HandheldFriendly" content="true"/> <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no"> <meta name="apple-mobile-web-app-capable" content="yes"> <meta name="apple-mobile-web-app-status-bar-style" content="black"> <link rel="apple-touch-icon-precomposed" sizes="152x152" href="../gitbook/images/apple-touch-icon-precomposed-152.png"> <link rel="shortcut icon" 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<ul> <li>Action 提交的是 mutation，而不是直接变更状态。</li> <li>Action 可以包含任意异步操作。</li> </ul> 让我们来注册一个简单的 action： <pre class="language-"><code class="lang-js">const store = new Vuex.Store({ state: { count: 0 }, mutations: { increment (state) { state.count++ } }, actions: { increment (context) { context.commit('increment') } } }) </code></pre> Action 函数接受一个与 store 实例具有相同方法和属性的 context 对象，因此你可以调用 <code>context.commit</code> 提交一个 mutation，或者通过 <code>context.state</code> 和 <code>context.getters</code> 来获取 state 和 getters。当我们在之后介绍到 <a href="modules.html">Modules</a> 时，你就知道 context 对象为什么不是 store 实例本身了。 实践中，我们会经常用到 ES2015 的 <a href="https://github.com/lukehoban/es6features#destructuring" target="_blank">参数解构</a> 来简化代码（特别是我们需要调用 <code>commit</code> 很多次的时候）： <pre class="language-"><code class="lang-js">actions: { increment ({ commit }) { commit('increment') } } </code></pre> <h3 id="分发-action">分发 Action</h3> Action 通过 <code>store.dispatch</code> 方法触发： <pre class="language-"><code class="lang-js">store.dispatch('increment') </code></pre> 乍一眼看上去感觉多此一举，我们直接分发 mutation 岂不更方便？实际上并非如此，还记得 mutation 必须同步执行这个限制么？Action 就不受约束！我们可以在 action 内部执行异步操作： <pre class="language-"><code class="lang-js">actions: { incrementAsync ({ commit }) { setTimeout(() => { commit('increment') }, 1000) } } </code></pre> Actions 支持同样的载荷方式和对象方式进行分发： <pre class="language-"><code class="lang-js">// 以载荷形式分发 store.dispatch('incrementAsync', { amount: 10 }) // 以对象形式分发 store.dispatch({ type: 'incrementAsync', amount: 10 }) </code></pre> 来看一个更加实际的购物车示例，涉及到调用异步 API 和分发多重 mutation： <pre class="language-"><code class="lang-js">actions: { checkout ({ commit, state }, products) { // 把当前购物车的物品备份起来 const savedCartItems = [...state.cart.added] // 发出结账请求，然后乐观地清空购物车 commit(types.CHECKOUT_REQUEST) // 购物 API 接受一个成功回调和一个失败回调 shop.buyProducts( products, // 成功操作 () => commit(types.CHECKOUT_SUCCESS), // 失败操作 () => commit(types.CHECKOUT_FAILURE, savedCartItems) ) } } </code></pre> 注意我们正在进行一系列的异步操作，并且通过提交 mutation 来记录 action 产生的副作用（即状态变更）。 <h3 id="在组件中分发-action">在组件中分发 Action</h3> 你在组件中使用 <code>this.$store.dispatch('xxx')</code> 分发 action，或者使用 <code>mapActions</code> 辅助函数将组件的 methods 映射为 <code>store.dispatch</code> 调用（需要先在根节点注入 <code>store</code>）： <pre class="language-"><code class="lang-js">import { mapActions } from 'vuex' export default { // ... methods: { ...mapActions([ 'increment', // 将 `this.increment()` 映射为 `this.$store.dispatch('increment')` // `mapActions` 也支持载荷： 'incrementBy' // 将 `this.incrementBy(amount)` 映射为 `this.$store.dispatch('incrementBy', amount)` ]), ...mapActions({ add: 'increment' // 将 `this.add()` 映射为 `this.$store.dispatch('increment')` }) } } </code></pre> <h3 id="组合-action">组合 Action</h3> Action 通常是异步的，那么如何知道 action 什么时候结束呢？更重要的是，我们如何才能组合多个 action，以处理更加复杂的异步流程？ 首先，你需要明白 <code>store.dispatch</code> 可以处理被触发的 action 的处理函数返回的 Promise，并且 <code>store.dispatch</code> 仍旧返回 Promise： <pre class="language-"><code class="lang-js">actions: { actionA ({ commit }) { return new Promise((resolve, reject) => { setTimeout(() => { commit('someMutation') resolve() }, 1000) }) } } </code></pre> 现在你可以： <pre class="language-"><code class="lang-js">store.dispatch('actionA').then(() => { // ... }) </code></pre> 在另外一个 action 中也可以： <pre class="language-"><code class="lang-js">actions: { // ... actionB ({ dispatch, commit }) { return dispatch('actionA').then(() => { commit('someOtherMutation') }) } } </code></pre> 最后，如果我们利用 <a href="https://tc39.github.io/ecmascript-asyncawait/" target="_blank">async / await</a>，我们可以如下组合 action： <pre class="language-"><code class="lang-js">// 假设 getData() 和 getOtherData() 返回的是 Promise actions: { async actionA ({ commit }) { commit('gotData', await getData()) }, async actionB ({ dispatch, commit }) { await dispatch('actionA') // 等待 actionA 完成 commit('gotOtherData', await getOtherData()) } } </code></pre> <blockquote> 一个 <code>store.dispatch</code> 在不同模块中可以触发多个 action 函数。在这种情况下，只有当所有触发函数完成后，返回的 Promise 才会执行。 </blockquote> </section> </div> 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