{"id":5650,"date":"2022-05-13T17:30:37","date_gmt":"2022-05-13T09:30:37","guid":{"rendered":"http:\/\/39.106.39.94\/?p=5650"},"modified":"2022-05-13T17:30:38","modified_gmt":"2022-05-13T09:30:38","slug":"reducer","status":"publish","type":"post","link":"https:\/\/lilichao.com\/?p=5650","title":{"rendered":"Reducer"},"content":{"rendered":"\n

\u5728React\u7684\u51fd\u6570\u7ec4\u4ef6\u4e2d\uff0c\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7useState()\u6765\u521b\u5efastate\u3002\u8fd9\u79cd\u521b\u5efastate\u7684\u65b9\u5f0f\u4f1a\u7ed9\u6211\u4eec\u8fd4\u56de\u4e24\u4e2a\u4e1c\u897fstate\u548csetState()\u3002state\u7528\u6765\u8bfb\u53d6\u6570\u636e\uff0c\u800csetState()\u7528\u6765\u8bbe\u7f6e\u4fee\u6539\u6570\u636e\u3002\u4f46\u662f\u8fd9\u79cd\u65b9\u5f0f\u4e5f\u5b58\u5728\u7740\u4e00\u4e9b\u4e0d\u8db3\uff0c\u56e0\u4e3a\u6240\u6709\u7684\u4fee\u6539state\u7684\u65b9\u5f0f\u90fd\u5fc5\u987b\u901a\u8fc7setState()\u6765\u8fdb\u884c\uff0c\u5982\u679c\u9047\u5230\u4e00\u4e9b\u590d\u6742\u5ea6\u6bd4\u8f83\u9ad8\u7684state\u65f6\uff0c\u8fd9\u79cd\u65b9\u5f0f\u4f3c\u4e4e\u5c31\u53d8\u5f97\u4e0d\u662f\u90a3\u4e48\u7684\u4f18\u96c5\u3002<\/p>\n\n\n\n

\u4e3e\u4e2a\u4f8b\u5b50\uff0c\u4e4b\u524d\u7684\u300a\u6c49\u5821\u5230\u5bb6\u300b\u7684\u7ec3\u4e60\u4e2d\uff0cApp.js<\/code>\u4e2d\u6709\u4e00\u4e2astate\u53eb\u505acartData<\/code>\u7528\u6765\u5b58\u50a8\u8d2d\u7269\u8f66\u6570\u636e\u3002\u4f46\u662f\u8fd9\u4e2a\u6570\u636e\u672c\u8eab\u662f\u6bd4\u8f83\u590d\u6742\u7684\uff0c\u5b83\u5305\u62ec\u4e86\u591a\u4e2a\u5c5e\u6027\uff1a<\/p>\n\n\n\n

const [cartData, setCartData] = useState<\/em>({\n    items: [],\n    totalAmount: 0,\n    totalPrice: 0\n});<\/pre>\n\n\n\n
\u540c\u65f6\u8d2d\u7269\u8f66\uff0c\u4e5f\u9700\u8981\u591a\u4e2a\u64cd\u4f5c\u65b9\u6cd5\uff0c\u50cf\u662f\u6dfb\u52a0\u98df\u7269\u3001\u5220\u9664\u98df\u7269\u3001\u6e05\u9664\u8d2d\u7269\u8f66\uff0c\u800cuseState()\u53ea\u7ed9\u6211\u4eec\u63d0\u4f9b\u4e86\u4e00\u4e2asetCartData()\u65b9\u6cd5\uff0c\u6240\u4ee5\u6211\u4eec\u4e0d\u5f97\u4e0d\u5728\u7ee7\u7eed\u521b\u5efa\u51fa\u4e09\u4e2a\u4e0d\u540c\u7684\u65b9\u6cd5\u4ee5\u5b9e\u73b0\u51fa\u4e0d\u540c\u7684\u529f\u80fd\uff1a<\/p>\n\n\n\n
const addItem = (meal) => {\n<\/em>    <\/em>const newCart = {...cartData};\n<\/em>    <\/em>if (newCart.items.indexOf(meal) === -1) {\n<\/em>        <\/em>newCart.items.push(meal);\n<\/em>        <\/em>meal.amount = 1;\n    } else {\n<\/em>        <\/em>meal.amount += 1;\n    }\n<\/em>    <\/em>newCart.totalAmount += 1;\n<\/em>    <\/em>newCart.totalPrice += meal.price;\n<\/em>    <\/em>setCartData(newCart);\n};\n\n<\/em>const removeItem = (meal) => {\n<\/em>    <\/em>const newCart = {...cartData};\n<\/em>    <\/em>meal.amount -= 1;\n<\/em>    <\/em>if (meal.amount === 0) {\n<\/em>        <\/em>newCart.items.splice(newCart.items.indexOf(meal), 1);\n    }\n<\/em>    <\/em>newCart.totalAmount -= 1;\n    newCart.totalPrice -= meal.price;\n    setCartData(newCart);\n};\n\nconst clearCart = () => {\n    const newCart = {...cartData};\n<\/em>    <\/em>newCart.items.forEach(item => delete item.amount);\n    newCart.items = [];\n    newCart.totalAmount = 0;\n    newCart.totalPrice = 0;\n    setCartData(newCart);\n};<\/pre>\n\n\n\n
\u8fd9\u4e09\u4e2a\u51fd\u6570\u5b9a\u4e49\u5728\u4e86App.js<\/code>\u4e2d\uff0c\u662f\u64cd\u4f5ccartData<\/code>\u7684\u4e09\u4e2a\u51fd\u6570\u3002\u5c31\u8fd9\u5e26\u6765\u4e00\u4e9b\u95ee\u9898\uff0c\u9996\u5148\uff0c\u4e09\u4e2a\u65b9\u6cd5\u90fd\u662f\u64cd\u4f5ccartData\u7684\uff0c\u4f46\u662f\u5b83\u4eec\u88ab\u5b9a\u4e49\u5728App.js<\/code>\u4e2d\u548c\u5176\u4ed6\u7684\u51fd\u6570\u6df7\u6742\u5728\u4e86\u4e00\u8d77\uff0c\u7ef4\u62a4\u8d77\u6765\u5e76\u4e0d\u65b9\u4fbf\u3002\u5176\u6b21\uff0c\u4e09\u4e2a\u65b9\u6cd5\u5e76\u4e0d\u662fApp.js<\/code>\u81ea\u5df1\u8c03\u7528\uff0c\u800c\u662f\u901a\u8fc7Context<\/code>\u4f20\u9012\u7ed9\u5176\u4ed6\u7ec4\u4ef6\u8c03\u7528\uff0c\u7531\u4e8e\u662f\u4e09\u4e2a\u51fd\u6570\u6240\u4ee5\u6211\u4eec\u4e0d\u5f97\u4e0d\u5728Context<\/code>\u4e2d\u5206\u522b\u4f20\u9012\u4e09\u4e2a\u5c5e\u6027\uff0c\u4e5f\u4e0d\u65b9\u4fbf\u3002\u518d\u6709\uff0c\u5982\u679c\u540e\u671f\u6211\u9700\u8981\u518d\u6dfb\u52a0\u65b0\u7684\u529f\u80fd\uff0c\u4f9d\u7136\u4e0d\u53ef\u907f\u514d\u7684\u8981\u5b9a\u4e49\u65b0\u7684\u51fd\u6570\uff0c\u5e76\u4e14\u4fee\u6539Context<\/code>\u3002\u603b\u4e4b\uff0c\u5c31\u662f\u5404\u79cd\u4e0d\u4fbf\u5229\uff0c\u8fd9\u79cd\u4e0d\u4fbf\u8fd8\u4f1a\u968f\u7740\u9879\u76ee\u590d\u6742\u7684\u63d0\u5347\u800c\u589e\u52a0\u3002<\/p>\n\n\n\n
Reducer\u6a2a\u7a7a\u51fa\u4e16<\/h2>\n\n\n\n
\u4e3a\u4e86\u89e3\u51b3\u590d\u6742State<\/code>\u5e26\u6765\u7684\u4e0d\u4fbf\uff0cReact<\/code>\u4e3a\u6211\u4eec\u63d0\u4f9b\u4e86\u4e00\u4e2a\u65b0\u7684\u4f7f\u7528State<\/code>\u7684\u65b9\u5f0f\u3002Reducer<\/code>\u6a2a\u7a7a\u51fa\u4e16\uff0creduce\u5355\u8bcd\u4e2d\u6587\u610f\u5473\u51cf\u5c11\uff0c\u800creducer\u6211\u89c9\u5f97\u53ef\u4ee5\u7ffb\u8bd1\u4e3a\u201c\u5f53\u4f60\u7684state\u7684\u8fc7\u4e8e\u590d\u6742\u65f6\uff0c\u4f60\u5c31\u53ef\u4ee5\u4f7f\u7528\u7684\u53ef\u4ee5\u5bf9state\u8fdb\u884c\u6574\u5408\u7684\u5de5\u5177\u201d\u3002\u5f53\u7136\u8fd9\u662f\u4e2a\u73a9\u7b11\u8bdd\uff0c\u4e2a\u4eba\u8ba4\u4e3aReducer<\/code>\u53ef\u4ee5\u7ffb\u8bd1\u4e3a\u201c\u6574\u5408\u5668\u201d\uff0c\u5b83\u7684\u4f5c\u7528\u5c31\u662f\u5c06\u90a3\u4e9b\u548c\u540c\u4e00\u4e2astate<\/code>\u76f8\u5173\u7684\u6240\u6709\u51fd\u6570\u90fd\u6574\u5408\u5230\u4e00\u8d77\uff0c\u65b9\u4fbf\u5728\u7ec4\u4ef6\u4e2d\u8fdb\u884c\u8c03\u7528\u3002<\/p>\n\n\n\n
\u5f53\u7136\u5de5\u5177\u90fd\u6709\u5176\u4f7f\u7528\u573a\u666f\uff0cReducer<\/code>\u4e5f\u4e0d\u4f8b\u5916\uff0c\u5b83\u53ea\u9002\u7528\u4e8e\u90a3\u4e9b\u6bd4\u8f83\u590d\u6742\u7684state<\/code>\uff0c\u5bf9\u4e8e\u7b80\u5355\u7684state<\/code>\u4f7f\u7528Reducer<\/code>\u53ea\u80fd\u662f\u5f92\u589e\u70e6\u607c\u3002\u4f46\u662f\u7531\u4e8e\u521d\u5b66\uff0c\u6211\u4eec\u4f1a\u5148\u7528\u4e00\u4e2a\u7b80\u5355\u7684\u6848\u4f8b\u6765\u5bf9\u5176\u8fdb\u884c\u6f14\u793a\uff0c\u5b9e\u9645\u5e94\u7528\u6211\u4eec\u540e\u8fb9\u4f1a\u4ee5cartData<\/code>\u4f5c\u4e3a\u6f14\u793a\u3002<\/p>\n\n\n\n
\u548cState<\/code>\u76f8\u540cReducer<\/code>\u4e5f\u662f\u4e00\u4e2a\u94a9\u5b50\u51fd\u6570\uff0c\u8bed\u6cd5\u5982\u4e0b\uff1a<\/p>\n\n\n\n
const [state, dispatch] = useReducer(reducer, initialArg, init);<\/code><\/pre>\n\n\n\n
\u5b83\u7684\u8fd4\u56de\u503c\u548cuseState()<\/code>\u7c7b\u4f3c\uff0c\u7b2c\u4e00\u4e2a\u53c2\u6570\u662fstate<\/code>\u7528\u6765\u8bfb\u53d6state<\/code>\u7684\u503c\uff0c\u7b2c\u4e8c\u4e2a\u53c2\u6570\u540c\u6837\u662f\u4e00\u4e2a\u51fd\u6570\uff0c\u4e0d\u540c\u4e8esetState()<\/code>\u8fd9\u4e2a\u51fd\u6570\u6211\u4eec\u53ef\u4ee5\u79f0\u5b83\u662f\u4e00\u4e2a\u201c\u6d3e\u53d1\u5668\u201d\uff0c\u901a\u8fc7\u5b83\u53ef\u4ee5\u5411reducer()<\/code>\u53d1\u9001\u4e0d\u540c\u7684\u6307\u4ee4\uff0c\u63a7\u5236reducer()<\/code>\u505a\u4e0d\u540c\u7684\u64cd\u4f5c\u3002<\/p>\n\n\n\n
\u5b83\u7684\u53c2\u6570\u6709\u4e09\u4e2a\uff0c\u7b2c\u4e09\u4e2a\u6211\u4eec\u6682\u4e14\u5ffd\u7565\uff0c\u53ea\u770b\u524d\u4e24\u4e2a\u3002reducer()<\/code>\u662f\u4e00\u4e2a\u51fd\u6570\uff0c\u4e5f\u662f\u6211\u4eec\u6240\u8c13\u7684\u201c\u6574\u5408\u5668\u201d\u3002\u5b83\u7684\u8fd4\u56de\u503c\u4f1a\u6210\u4e3a\u65b0\u7684state<\/code>\u503c\u3002\u5f53\u6211\u4eec\u8c03\u7528dispatch()<\/code>\u65f6\uff0cdispatch()<\/code>\u4f1a\u5c06\u6d88\u606f\u53d1\u9001\u7ed9reducer()<\/code>\uff0creducer()<\/code>\u53ef\u4ee5\u6839\u636e\u4e0d\u540c\u7684\u6d88\u606f\u5bf9state<\/code>\u8fdb\u884c\u4e0d\u540c\u7684\u5904\u7406\u3002initialArg<\/code>\u5c31\u662fstate<\/code>\u7684\u521d\u59cb\u503c\uff0c\u548cuseState()<\/code>\u53c2\u6570\u4e00\u6837\u3002<\/p>\n\n\n\n
\u4e0a\u4ee3\u7801\uff1a<\/p>\n\n\n\n
import {useReducer<\/em>, useState<\/em>} from 'react';\n\nconst reducer = (state, action) => {\n    switch(action.type){\n        case 'add':\n            return state + 1;\n        case 'sub':\n            return state - 1;\n    }\n};\n\nfunction App<\/em>() {\n\n<\/em>    <\/em>const [count, countDispath] = useReducer<\/em>(reducer,1);\n\n    return (\n        <div className=\"App\">\n            {count}\n\n            <div>\n                <button onClick={()=>countDispath({type:'sub'})}>-<\/button>\n                <button onClick={()=>countDispath({type:'add'})}>+<\/button>\n            <\/div>\n        <\/div>\n    );\n}\n\nexport default App<\/em>;<\/pre>\n\n\n\n
\u4e0d\u77e5\u9053\u4ee3\u7801\u4f60\u80fd\u4e0d\u770b\u61c2\uff0c\u4e0d\u8fc7\u6211\u4e5f\u662f\u4e0d\u60f3\u5206\u6790\u4e86\uff0c\u4e0d\u5199\u4e86\u770b\u89c6\u9891\u5427\u3002<\/p>\n\n\n\n
\u4fee\u6539\u8d2d\u7269\u8f66<\/h2>\n\n\n\n
\u4fee\u6539App.js<\/code><\/p>\n\n\n\n
...\u7565...\nconst cartReducer = (state, action) => {\n    const newCart = {...state};\n    switch (action.type){\n        case 'ADD_ITEM':\n            if (newCart.items.indexOf(action.meal) === -1) {\n                newCart.items.push(action.meal);\n                action.meal.amount = 1;\n            } else {\n                action.meal.amount += 1;\n            }\n            newCart.totalAmount += 1;\n            newCart.totalPrice += action.meal.price;\n            return newCart;\n        case 'REMOVE_ITEM':\n            action.meal.amount -= 1;\n            if (action.meal.amount === 0) {\n                newCart.items.splice(newCart.items.indexOf(action.meal), 1);\n            }\n            newCart.totalAmount -= 1;\n            newCart.totalPrice -= action.meal.price;\n            return newCart;\n        case 'CLEAR_CART':\n            newCart.items.forEach(item => delete item.amount);\n            newCart.items = [];\n            newCart.totalAmount = 0;\n            newCart.totalPrice = 0;\n            return newCart;\n        default:\n            return state;\n    }\n};\n\nconst App <\/em>= () => {\n\n    ...\u7565...\n\n    <\/em>const [cartData, cartDispatch] = useReducer<\/em>(cartReducer, {\n        items: [],\n        totalAmount: 0,\n        totalPrice: 0\n    });\n\n    ...\u7565...<\/em>\n\n    return (\n        <CartContext.Provider value={{...cartData, cartDispatch}}>\n            <div>\n                <FilterMeals onFilter={filterHandler}\/>\n                <Meals\n                    mealsData={mealsData}\n                \/>\n                <Cart\/>\n\n            <\/div>\n        <\/CartContext.Provider>\n    );\n};\n\nexport default App<\/em>;<\/pre>\n\n\n\n
\u5728\u5176\u4ed6\u7ec4\u4ef6\u4e2d\uff0c\u9700\u8981\u64cd\u4f5c\u8d2d\u7269\u8f66\u65f6\uff0c\u53ea\u9700\u5148\u83b7\u53d6CartContext<\/code>\u7136\u540e\u901a\u8fc7ctx.cartDispath<\/code>\u64cd\u4f5c\u8d2d\u7269\u8f66\uff1a<\/p>\n\n\n\n
const ctx = useContext<\/em>(CartContext); \/\/ \u52a0\u8f7dcontext\nctx.cartDispatch({type:'CLEAR_CART'}); \/\/ \u6e05\u7a7a\u8d2d\u7269\u8f66\nctx.cartDispatch({type:'ADD_ITEM', meal:props.meal}); \/\/ \u6dfb\u52a0\u98df\u7269\nctx.cartDispatch({type:'REMOVE_ITEM', meal:props.meal}); \/\/ \u5220\u9664\u98df\u7269<\/pre>\n","protected":false},"excerpt":{"rendered":"
\u5728React\u7684\u51fd\u6570\u7ec4\u4ef6\u4e2d\uff0c\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7useState()\u6765\u521b\u5efastate\u3002\u8fd9\u79cd\u521b\u5efastate\u7684\u65b9\u5f0f\u4f1a\u7ed9\u6211\u4eec\u8fd4 […]<\/p>\n","protected":false},"author":1,"featured_media":5654,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[198],"tags":[200,202,199,201,203],"_links":{"self":[{"href":"https:\/\/lilichao.com\/index.php?rest_route=\/wp\/v2\/posts\/5650"}],"collection":[{"href":"https:\/\/lilichao.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lilichao.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lilichao.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/lilichao.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5650"}],"version-history":[{"count":5,"href":"https:\/\/lilichao.com\/index.php?rest_route=\/wp\/v2\/posts\/5650\/revisions"}],"predecessor-version":[{"id":5848,"href":"https:\/\/lilichao.com\/index.php?rest_route=\/wp\/v2\/posts\/5650\/revisions\/5848"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/lilichao.com\/index.php?rest_route=\/wp\/v2\/media\/5654"}],"wp:attachment":[{"href":"https:\/\/lilichao.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5650"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lilichao.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5650"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lilichao.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5650"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}