vuex-help

<!DOCTYPE HTML> <html lang="zh-cn" > <head> <meta charset="UTF-8"> <meta content="text/html; charset=utf-8" http-equiv="Content-Type"> <title>Getter · 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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href="getting-started.html"> 开始 </a> </li> <li class="chapter " data-level="1.6" data-path="core-concepts.html"> <a href="core-concepts.html"> 核心概念 </a> <ul class="articles"> <li class="chapter " data-level="1.6.1" data-path="state.html"> <a href="state.html"> State </a> </li> <li class="chapter active" data-level="1.6.2" data-path="getters.html"> <a href="getters.html"> Getter </a> </li> <li class="chapter " data-level="1.6.3" data-path="mutations.html"> <a href="mutations.html"> Mutation </a> </li> <li class="chapter " data-level="1.6.4" data-path="actions.html"> <a href="actions.html"> Action </a> </li> <li class="chapter " data-level="1.6.5" data-path="modules.html"> <a href="modules.html"> Module </a> </li> </ul> </li> <li class="chapter " data-level="1.7" data-path="structure.html"> <a href="structure.html"> 项目结构 </a> </li> <li class="chapter " data-level="1.8" data-path="plugins.html"> <a href="plugins.html"> 插件 </a> </li> <li class="chapter " data-level="1.9" 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中派生出一些状态，例如对列表进行过滤并计数： <pre class="language-"><code class="lang-js">computed: { doneTodosCount () { return this.$store.state.todos.filter(todo => todo.done).length } } </code></pre> 如果有多个组件需要用到此属性，我们要么复制这个函数，或者抽取到一个共享函数然后在多处导入它——无论哪种方式都不是很理想。 Vuex 允许我们在 store 中定义“getter”（可以认为是 store 的计算属性）。就像计算属性一样，getter 的返回值会根据它的依赖被缓存起来，且只有当它的依赖值发生了改变才会被重新计算。 Getter 接受 state 作为其第一个参数： <pre class="language-"><code class="lang-js">const store = new Vuex.Store({ state: { todos: [ { id: 1, text: '...', done: true }, { id: 2, text: '...', done: false } ] }, getters: { doneTodos: state => { return state.todos.filter(todo => todo.done) } } }) </code></pre> Getter 会暴露为 <code>store.getters</code> 对象： <pre class="language-"><code class="lang-js">store.getters.doneTodos // -> [{ id: 1, text: '...', done: true }] </code></pre> Getter 也可以接受其他 getter 作为第二个参数： <pre class="language-"><code class="lang-js">getters: { // ... doneTodosCount: (state, getters) => { return getters.doneTodos.length } } </code></pre> <pre class="language-"><code class="lang-js">store.getters.doneTodosCount // -> 1 </code></pre> 我们可以很容易地在任何组件中使用它： <pre class="language-"><code class="lang-js">computed: { doneTodosCount () { return this.$store.getters.doneTodosCount } } </code></pre> 你也可以通过让 getter 返回一个函数，来实现给 getter 传参。在你对 store 里的数组进行查询时非常有用。 <pre class="language-"><code class="lang-js">getters: { // ... getTodoById: (state) => (id) => { return state.todos.find(todo => todo.id === id) } } </code></pre> <pre class="language-"><code class="lang-js">store.getters.getTodoById(2) // -> { id: 2, text: '...', done: false } </code></pre> <h3 id="mapgetters-辅助函数"><code>mapGetters</code> 辅助函数</h3> <code>mapGetters</code> 辅助函数仅仅是将 store 中的 getter 映射到局部计算属性： <pre class="language-"><code class="lang-js">import { mapGetters } from 'vuex' export default { // ... computed: { // 使用对象展开运算符将 getter 混入 computed 对象中 ...mapGetters([ 'doneTodosCount', 'anotherGetter', // ... ]) } } </code></pre> 如果你想将一个 getter 属性另取一个名字，使用对象形式： <pre class="language-"><code class="lang-js">mapGetters({ // 映射 `this.doneCount` 为 `store.getters.doneTodosCount` doneCount: 'doneTodosCount' }) </code></pre> </section> </div> <div class="search-results"> <div class="has-results"> <h1 class="search-results-title"> results matching ""</h1> <ul class="search-results-list"></ul> </div> <div class="no-results"> <h1 class="search-results-title">No results matching ""</h1> </div> </div> </div> </div> </div> <script src="//m.servedby-buysellads.com/monetization.js" type="text/javascript"></script> <div class="bsa-cpc"></div> <script> (function(){ if(typeof _bsa !== 'undefined' && _bsa) { _bsa.init('default', 'CKYD62QM', 'placement:vuejsorg', { target: '.bsa-cpc', align: 'horizontal', disable_css: 'true' }); } })(); </script> </div> <a href="state.html" class="navigation navigation-prev " aria-label="Previous page: State"> </a> <a href="mutations.html" class="navigation navigation-next " aria-label="Next page: Mutation"> </a> </div> <script> var 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