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<!DOCTYPE HTML> <html lang="ja" > <head> <meta charset="UTF-8"> <meta content="text/html; charset=utf-8" http-equiv="Content-Type"> <title>ゲッター · 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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例えば項目のリストをフィルタリングしたりカウントするときのように、ストアの状態を算出したいときがあります。 <pre class="language-"><code class="lang-js">computed: { doneTodosCount () { return this.$store.state.todos.filter(todo => todo.done).length } } </code></pre> もしこの関数を複数のコンポーネントで利用したくなったら、関数をコピーするか、あるいは関数を共用のヘルパーに切り出して複数の場所でインポートする必要があります。しかし、どちらも理想的とはいえません。 Vuex を利用するとストア内に "ゲッター" を定義することができます。それらをストアの算出プロパティと考えることができます。算出プロパティと同様に、ゲッターの結果はその依存関係に基づいて計算され、依存関係の一部が変更されたときにのみ再評価されます。 ゲッターは第1引数として、state を受け取ります: <pre class="language-"><code class="lang-js">const store = new Vuex.Store({ state: { todos: [ { id: 1, text: '...', done: true }, { id: 2, text: '...', done: false } ] }, getters: { doneTodos: state => { return state.todos.filter(todo => todo.done) } } }) </code></pre> ゲッターは <code>store.getters</code> オブジェクトから取り出されます: <pre class="language-"><code class="lang-js">store.getters.doneTodos // -> [{ id: 1, text: '...', done: true }] </code></pre> ゲッターは第2引数として他のゲッターを受け取ります: <pre class="language-"><code class="lang-js">getters: { // ... doneTodosCount: (state, getters) => { return getters.doneTodos.length } } </code></pre> <pre class="language-"><code class="lang-js">store.getters.doneTodosCount // -> 1 </code></pre> どのコンポーネントの内部でも簡単にゲッターを利用することができます: <pre class="language-"><code class="lang-js">computed: { doneTodosCount () { return this.$store.getters.doneTodosCount } } </code></pre> 関数を返り値にすることで、ゲッターに引数を渡すこともできます。これは特にストアの中の配列を検索する時に役立ちます： <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-ヘルパー"><code>mapGetters</code> ヘルパー</h3> <code>mapGetters</code> ヘルパーはストアのゲッターをローカルの算出プロパティにマッピングさせます: <pre class="language-"><code class="lang-js">import { mapGetters } from 'vuex' export default { // ... computed: { // ゲッターを、スプレッド演算子（object spread operator）を使って computed に組み込む ...mapGetters([ 'doneTodosCount', 'anotherGetter', // ... ]) } } </code></pre> ゲッターを異なる名前でマッピングさせたいときはオブジェクトを使います: <pre class="language-"><code class="lang-js">...mapGetters({ // `this.doneCount` を `store.getters.doneTodosCount` にマッピングさせる 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 " 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