{"id":5811,"date":"2024-02-09T20:37:32","date_gmt":"2024-02-09T11:37:32","guid":{"rendered":"https:\/\/www.searchlight8.com\/?p=5811"},"modified":"2024-02-09T20:37:32","modified_gmt":"2024-02-09T11:37:32","slug":"react-usereducer","status":"publish","type":"post","link":"https:\/\/www.searchlight8.com\/wp-searchlight8\/react-usereducer\/","title":{"rendered":"[React] useReducer"},"content":{"rendered":"\n

useReducer\u306fReact\u306eHook\u306e\u3072\u3068\u3064\u3067\u3001useState\u306b\u6bd4\u3079\u3066\u3088\u308a\u8907\u96d1\u306a\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u306e\u72b6\u614b\u7ba1\u7406\u3092\u53ef\u80fd\u306b\u3057\u307e\u3059\u3002\u7c21\u5358\u306a\u5229\u7528\u4f8b\u306f\u300c\uff0b\u300d\u300c\uff0d\u300d\u300c\u30ea\u30bb\u30c3\u30c8\u300d\u30dc\u30bf\u30f3\u304c\u3042\u308a\u3001\u6570\u5b57\u306e\u52a0\u7b97\u30fb\u6e1b\u7b97\u30fb\u30ea\u30bb\u30c3\u30c8\u3092\u7ba1\u7406\u3059\u308b\u3088\u3046\u306a\u3068\u304d\u306b\u306a\u308a\u307e\u3059\u3002<\/p>\n\n\n\n

useReducer\u3068useState\u306e\u9055\u3044<\/h3>\n\n\n\n
<\/td>useReducer<\/td>useState<\/td><\/tr>
\u5b9a\u7fa9\u5f0f<\/td>
const [state, dispatch] = useReducer(reducer, initialState);<\/code><\/td>		const [state, setState] = useState(initialState);<\/td><\/tr>
\u5b9f\u88c5<\/td>\u95a2\u6570\u306e\u5b9a\u7fa9\u6642\u306b\u66f4\u65b0\u306e\u65b9\u6cd5\u3092\u6c7a\u3081\u308b\u3002<\/td>\u5024\u306e\u5909\u66f4\u3092\u3057\u305f\u3044\u3068\u304d\u306b\u66f4\u65b0\u306e\u65b9\u6cd5\u3092\u6c7a\u3081\u308b\u3002<\/td><\/tr>
\u5229\u7528\u30b1\u30fc\u30b9<\/td>\u8907\u6570\u306e\u72b6\u614b\u30fb\u8907\u96d1\u306a\u30ed\u30b8\u30c3\u30af\u7ba1\u7406<\/td>\u30b7\u30f3\u30d7\u30eb\u306a\u72b6\u614b\u7ba1\u7406<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

const [state, dispatch] = useReducer(reducer, initialState); <\/strong><\/p>\n\n\n\n

    \n
  • \u5de6\u8fba\u306estate\u306f\u73fe\u5728\u306e\u72b6\u614b<\/li>\n\n\n\n
  • \u5de6\u8fba\u306edispach\u306freducer\u3092\u5b9f\u884c\u3059\u308b\u305f\u3081\u306e\u95a2\u6570<\/li>\n\n\n\n
  • \u53f3\u8fba\u306ereduer\u306fstate\u3092\u66f4\u65b0\u3059\u305f\u3081\u306e\u95a2\u6570\u3002state \u3068action\u3092\u53d7\u3051\u53d6\u308a\u3001\u65b0\u3057\u3044stete\u3092\u8fd4\u3059 <\/li>\n\n\n\n
  • \u53f3\u8fba\u306einitialState\u306fstate\u306e\u521d\u671f\u5024\u3092\u30bb\u30c3\u30c8<\/li>\n\n\n\n
  • \u53f3\u8fba\u306b\u306f\u7701\u7565\u53ef\u80fd\u306a\u7b2c\u4e09\u5f15\u6570 init \u3082\u3042\u308b\u3002\u3053\u308c\u306f\u521d\u671fstate\u3092\u8fd4\u3059\u3002\u6307\u5b9a\u3055\u308c\u3066\u3044\u306a\u3044\u5834\u5408\u306finitialSate\u306b\u306a\u308b\u3002<\/li>\n<\/ul>\n\n\n\n

    useReducer\u3092\u4f7f\u3063\u305f\u30ab\u30a6\u30f3\u30bf\u30fc\u306e\u5b9f\u88c5\u4f8b<\/h3>\n\n\n\n

    \u4e0b\u8a18\u306e\u3088\u3046\u306a\u7c21\u5358\u306a\u30ab\u30a6\u30f3\u30bf\u30fc\u3092\u4f5c\u3063\u3066\u307f\u307e\u3059\u3002\u52a0\u7b97\u30fb\u6e1b\u7b97\u30fb5\u305a\u3064\u52a0\u7b97\u30fb\u30af\u30ea\u30a2\u306e\uff14\u3064\u306e\u30dc\u30bf\u30f3\u3092\u4f5c\u308a\u3001\u30dc\u30bf\u30f3\u3092\u62bc\u3059\u3068\u4e0a\u306e\u30ab\u30a6\u30f3\u30c8\u306e\u8868\u793a\u304c\u5909\u5316\u3057\u307e\u3059\u3002<\/p>\n\n\n\n

    \"\"<\/figure>\n\n\n\n

    <\/p>\n\n\n\n

    import { useReducer } from \"react\";\n\nconst reducer = (prev, { type, plusNum }) => {\n  switch (type) {\n    case \"plus\":\n      return ++prev;\n    case \"minus\":\n      return --prev;\n    case \"addNum\":\n      return prev + plusNum;\n    case \"clear\":\n      return 0;\n    default:\n      throw new Error(\"action\u3092\u6b63\u3057\u304f\u8a2d\u5b9a\u3057\u3066\u304f\u3060\u3055\u3044\u3002\");\n  }\n};\n\nconst Sample = () => {\n  const [state, dispatch] = useReducer(reducer, 0);\n  const countUp = () => {\n    dispatch({ type: \"plus\" });\n  };\n  const countDown = () => {\n    dispatch({ type: \"minus\" });\n  };\n  const countPlusNum = () => {\n    dispatch({ type: \"addNum\", plusNum: 5 });\n  };\n  const countClear = () => {\n    dispatch({ type: \"clear\" });\n  };\n  return (\n    <>\n      <p>\u30ab\u30a6\u30f3\u30c8: {state}<\/p>\n      <button onClick={countUp}>+<\/button>\n      <button onClick={countDown}>-<\/button>\n      <button onClick={countPlusNum}>+5<\/button>\n      <button onClick={countClear}>\u30af\u30ea\u30a2<\/button>\n    <\/>\n  );\n};\n\nexport default Sample;<\/pre><\/div>\n\n\n\n
    const reducer = (prev, { type, plusNum }) => {} \u306e\u5f62\u3067reducer\u306e\u4e2d\u8eab\u3092\u8a18\u8ff0\u3057\u307e\u3059\u3002<\/p>\n\n\n\n
    \u7b2c\u4e00\u5f15\u6570\u300cprev\u300d\u306f\u524d\u306e\u5024<\/p>\n\n\n\n
    \u7b2c\u4e8c\u5f15\u6570\u306f\u300cdispach\u30bf\u30a4\u30d7, \u4efb\u610f\u306e\u30d7\u30ed\u30d1\u30c6\u30a3\u300d\u306b\u306a\u3063\u3066\u3044\u307e\u3059\u3002\u4eca\u56de\u306f\u4efb\u610f\u306e\u30d7\u30ed\u30d1\u30c6\u30a3\u306f\u52a0\u7b97\u3059\u308b\u6570\u304c\u5165\u3063\u3066\u3044\u307e\u3059\u30021\u3092\u52a0\u7b97\u30fb\u6e1b\u7b97\u3059\u308b\u306e\u306fprev+1\u3084prev-1\u3067\u8a08\u7b97\u3057\u30012\u4ee5\u4e0a\u306e\u6570\u3092\u52a0\u7b97\u3059\u308b\u3068\u304d\u306fplusNum\u306b\u6570\u5b57\u3092\u8a2d\u5b9a\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n\n\n\n
    <\/p>\n\n\n\n
    \"\"<\/figure>\n\n\n\n
    \u3000reducer\u3067\u306f\u300c\u73fe\u5728\u306e\u5024\uff08\u524d\u306e\u5024\uff09\u300d\u300cdispatch\u30bf\u30a4\u30d7\u300d\u300c\u4efb\u610f\u306e\u30d7\u30ed\u30d1\u30c6\u30a3\uff08\u5024\uff09\u300d\u3092\u53d7\u3051\u53d6\u308acase\u6587\u3067\u51e6\u7406\u3057\u3066\u5024\u3092\u8fd4\u3057\u307e\u3059\u3002<\/p>\n\n\n\n
    \u51e6\u7406\u306e\u307e\u3068\u3081<\/h3>\n\n\n\n
      \n
    • \uff11\uff0e\u767a\u706b\u70b9\u3092\u4f5c\u308b\uff08\u4eca\u56de\u306f\u30dc\u30bf\u30f3\u306eonClick\uff09<\/li>\n\n\n\n
    • \uff12\uff0e\u767a\u706b\u70b9\u306b\u5bfe\u5fdc\u3059\u308b\u95a2\u6570\u3092\u4f5c\u308b dispatch{(type : ” “)}  \u3092\u5b9f\u884c\u3002<\/li>\n\n\n\n
    • \uff13\uff0ereducer\u95a2\u6570\u3067\u524d\u306e\u5024\u3092\u5909\u66f4\u3059\u308b\u51e6\u7406\u3092\u5b9f\u884c<\/li>\n\n\n\n
    • \uff14\uff0estate\u304c\u65b0\u3057\u3044\u5024\u306b\u66f4\u65b0\u3055\u308c\u308b<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"
      useReducer\u306fReact\u306eHoo…<\/p>\n","protected":false},"author":1,"featured_media":2897,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[323],"tags":[324,446],"class_list":["post-5811","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-react","tag-react","tag-usereducer","wpcat-323-id"],"_links":{"self":[{"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/posts\/5811","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/comments?post=5811"}],"version-history":[{"count":10,"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/posts\/5811\/revisions"}],"predecessor-version":[{"id":5862,"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/posts\/5811\/revisions\/5862"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/media\/2897"}],"wp:attachment":[{"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/media?parent=5811"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/categories?post=5811"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.searchlight8.com\/wp-searchlight8\/wp-json\/wp\/v2\/tags?post=5811"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}