{"id":38378,"date":"2023-04-04T05:11:45","date_gmt":"2023-08-22T09:11:02","guid":{"rendered":"https:\/\/www.silicloud.com\/zh\/blog\/%e3%80%90react%e3%80%91%e4%bd%bf%e7%94%a8usememo%e6%9d%a5%e6%94%b9%e5%96%84contextapiusestate%e7%9a%84%e6%b8%b2%e6%9f%93%e6%80%a7%e8%83%bd\/"},"modified":"2024-04-29T21:49:42","modified_gmt":"2024-04-29T13:49:42","slug":"%e3%80%90react%e3%80%91%e4%bd%bf%e7%94%a8usememo%e6%9d%a5%e6%94%b9%e5%96%84contextapiusestate%e7%9a%84%e6%b8%b2%e6%9f%93%e6%80%a7%e8%83%bd","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/zh\/blog\/%e3%80%90react%e3%80%91%e4%bd%bf%e7%94%a8usememo%e6%9d%a5%e6%94%b9%e5%96%84contextapiusestate%e7%9a%84%e6%b8%b2%e6%9f%93%e6%80%a7%e8%83%bd\/","title":{"rendered":"\u3010React\u3011\u4f7f\u7528useMemo\u6765\u6539\u5584ContextAPI+useState\u7684\u6e32\u67d3\u6027\u80fd"},"content":{"rendered":"

\u9996\u5148<\/h1>\n

\u8bf7\u6ce8\u610f\uff0c\u6211\u53ea\u80fd\u63d0\u4f9b\u82f1\u8bed\u7ffb\u8bd1\u3002<\/p>\n

\u5728React\u7684ContextAPI\u4e2d\uff0c\u5982\u679c\u4e0d\u5c0f\u5fc3\u6ee5\u7528useState\uff0c\u4f1a\u5bfc\u81f4\u6e32\u67d3\u6210\u672c\u589e\u52a0\uff0c\u4ece\u800c\u5bfc\u81f4\u6027\u80fd\u4e0b\u964d\u7684\u53ef\u80fd\u6027\u3002\u56e0\u6b64\uff0c\u672c\u6587\u4ecb\u7ecd\u4e86\u4e00\u79cd\u901a\u8fc7\u4f7f\u7528useMemo\u6765\u9009\u62e9\u6027\u5730\u7f16\u5199\u91cd\u65b0\u6e32\u67d3\u7ec4\u4ef6\u4ee5\u63d0\u9ad8\u6027\u80fd\u7684\u65b9\u6cd5\u3002<\/p>\n

\u7ec4\u4ef6\u7ed3\u6784<\/h1>\n
\"image.png\"<\/div>\n

(\u4e3a\u4e86\u65b9\u4fbf\u7406\u89e3\uff0c\u5728\u8fd9\u91cc\u6211\u4eec\u6839\u636e\u9700\u8981\u4e3a\u7ec4\u4ef6\u5e94\u7528\u4e86\u76f8\u5e94\u7684CSS)<\/p>\n

\u6ca1\u6709\u5bf9\u7b56\u7684\u7248\u672c<\/h1>\n

\u4ee3\u7801\u793a\u4f8b<\/h2>\n
import<\/span> {<\/span> createContext<\/span> }<\/span> from<\/span> \"<\/span>react<\/span>\"<\/span>;<\/span>\r\n\r\n\/\/ Context\u306e\u578b\u3092\u5b9a\u7fa9<\/span>\r\ntype<\/span> ValueContextType<\/span> =<\/span> {<\/span>\r\n  value1<\/span>:<\/span> number<\/span>;<\/span>\r\n  updateValue1<\/span>:<\/span> (<\/span>_<\/span>:<\/span> number<\/span>)<\/span> =><\/span> void<\/span>;<\/span>\r\n  value2<\/span>:<\/span> number<\/span>;<\/span>\r\n  updateValue2<\/span>:<\/span> (<\/span>_<\/span>:<\/span> number<\/span>)<\/span> =><\/span> void<\/span>;<\/span>\r\n  value3<\/span>:<\/span> number<\/span>;<\/span>\r\n  updateValue3<\/span>:<\/span> (<\/span>_<\/span>:<\/span> number<\/span>)<\/span> =><\/span> void<\/span>;<\/span>\r\n};<\/span>\r\n\r\n\/\/ Context\u3092\u4f5c\u6210<\/span>\r\nconst<\/span> ValueContext<\/span> =<\/span> createContext<\/span><<\/span>ValueContextType<\/span>><\/span>(<\/span>null<\/span>!<\/span>);<\/span>\r\n\r\n\/\/ Provider\u3092\u4f5c\u6210<\/span>\r\nconst<\/span> ValueProvider<\/span> =<\/span> ({<\/span> children<\/span> }:<\/span> {<\/span> children<\/span>:<\/span> JSX<\/span>.<\/span>Element<\/span> })<\/span> =><\/span> {<\/span>\r\n  const<\/span> [<\/span>value1<\/span>,<\/span> setValue1<\/span>]<\/span> =<\/span> useState<\/span>(<\/span>0<\/span>);<\/span>\r\n\r\n  const<\/span> updateValue1<\/span> =<\/span> (<\/span>value<\/span>:<\/span> number<\/span>)<\/span> =><\/span> {<\/span>\r\n    setValue1<\/span>(<\/span>value<\/span>);<\/span>\r\n  };<\/span>\r\n\r\n  const<\/span> [<\/span>value2<\/span>,<\/span> setValue2<\/span>]<\/span> =<\/span> useState<\/span>(<\/span>0<\/span>);<\/span>\r\n\r\n  const<\/span> updateValue2<\/span> =<\/span> (<\/span>value<\/span>:<\/span> number<\/span>)<\/span> =><\/span> {<\/span>\r\n    setValue2<\/span>(<\/span>value<\/span>);<\/span>\r\n  };<\/span>\r\n\r\n  const<\/span> [<\/span>value3<\/span>,<\/span> setValue3<\/span>]<\/span> =<\/span> useState<\/span>(<\/span>0<\/span>);<\/span>\r\n\r\n  const<\/span> updateValue3<\/span> =<\/span> (<\/span>value<\/span>:<\/span> number<\/span>)<\/span> =><\/span> {<\/span>\r\n    setValue3<\/span>(<\/span>value<\/span>);<\/span>\r\n  };<\/span>\r\n  \r\n  return <\/span>(<\/span>\r\n    <<\/span>ValueContext<\/span>.<\/span>Provider<\/span> value<\/span>=<\/span>{<\/span>{<\/span>\r\n      value1<\/span>,<\/span>\r\n      updateValue1<\/span>;<\/span>\r\n      value2<\/span>,<\/span>\r\n      updateValue2<\/span>;<\/span>\r\n      value3<\/span>,<\/span>\r\n      updateValue3<\/span>;<\/span>\r\n    }<\/span>}<\/span>><\/span>\r\n      {<\/span>children<\/span>}<\/span>\r\n    <\/<\/span>ValueContext<\/span>.<\/span>Provider<\/span>><\/span>\r\n  );<\/span>\r\n};<\/span>\r\n\r\n\/\/ Context\u3068Provider\u3092\u30a8\u30af\u30b9\u30dd\u30fc\u30c8<\/span>\r\nexport<\/span> {<\/span> ValueContext<\/span>,<\/span> ValueProvider<\/span> };<\/span>\r\n<\/code><\/pre>\n
import<\/span> {<\/span> useContext<\/span> }<\/span> from<\/span> \"<\/span>react<\/span>\"<\/span>;<\/span>\r\nimport<\/span> {<\/span> ValueContext<\/span> }<\/span> from<\/span> \"<\/span>.\/Context.tsx<\/span>\"<\/span>;<\/span>\r\nimport<\/span> Child1<\/span> from<\/span> \"<\/span>.\/Child1<\/span>\"<\/span>;<\/span>\r\nimport<\/span> Child2<\/span> from<\/span> \"<\/span>.\/Child2<\/span>\"<\/span>;<\/span>\r\n\r\n\/\/ Parent\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8<\/span>\r\nconst<\/span> Parent<\/span> =<\/span> ()<\/span> =><\/span> {<\/span>\r\n  console<\/span>.<\/span>log<\/span>(<\/span>\"<\/span>re-rendered Parent<\/span>\"<\/span>);<\/span>\r\n  const<\/span> {<\/span> value1<\/span>,<\/span> updateValue1<\/span> }<\/span> =<\/span> useContext<\/span>(<\/span>ValueContext<\/span>);<\/span>\r\n\r\n  return <\/span>(<\/span>\r\n    <<\/span>div<\/span>><\/span>\r\n      <<\/span>h2<\/span>><\/span>Parent<\/<\/span>h2<\/span>><\/span>\r\n      <<\/span>p<\/span>><\/span>{<\/span>value1<\/span>}<\/span><\/<\/span>p<\/span>><\/span>\r\n      <<\/span>button<\/span> type<\/span>=<\/span>\"button\"<\/span> onClick<\/span>=<\/span>{<\/span>()<\/span> =><\/span> {<\/span>\r\n        updateValue1<\/span>(<\/span>value1<\/span> +<\/span> 1<\/span>);<\/span>\r\n      }<\/span>}<\/span>><\/span>+<\/<\/span>button<\/span>><\/span>\r\n      <<\/span>Child1<\/span> \/><\/span>\r\n      <<\/span>Child2<\/span> \/><\/span>\r\n    <\/<\/span>div<\/span>><\/span>\r\n  );<\/span>\r\n};<\/span>\r\n\r\nexport<\/span> default<\/span> Parent<\/span>;<\/span>\r\n<\/code><\/pre>\n
import<\/span> {<\/span> useContext<\/span> }<\/span> from<\/span> \"<\/span>react<\/span>\"<\/span>;<\/span>\r\nimport<\/span> {<\/span> ValueContext<\/span> }<\/span> from<\/span> \"<\/span>.\/Context.tsx<\/span>\"<\/span>;<\/span>\r\n\r\n\/\/ Child1\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8<\/span>\r\nconst<\/span> Child1<\/span> =<\/span> ()<\/span> =><\/span> {<\/span>\r\n  console<\/span>.<\/span>log<\/span>(<\/span>\"<\/span>re-rendered Child1<\/span>\"<\/span>);<\/span>\r\n  const<\/span> {<\/span> value2<\/span>,<\/span> updateValue2<\/span> }<\/span> =<\/span> useContext<\/span>(<\/span>ValueContext<\/span>);<\/span>\r\n\r\n  return <\/span>(<\/span>\r\n    <<\/span>div<\/span>><\/span>\r\n      <<\/span>h2<\/span>><\/span>Child1<\/<\/span>h2<\/span>><\/span>\r\n      <<\/span>p<\/span>><\/span>{<\/span>value2<\/span>}<\/span><\/<\/span>p<\/span>><\/span>\r\n      <<\/span>button<\/span> type<\/span>=<\/span>\"button\"<\/span> onClick<\/span>=<\/span>{<\/span>()<\/span> =><\/span> {<\/span>\r\n        updateValue2<\/span>(<\/span>value2<\/span> +<\/span> 1<\/span>);<\/span>\r\n      }<\/span>}<\/span>><\/span>+<\/<\/span>button<\/span>><\/span>\r\n    <\/<\/span>div<\/span>><\/span>\r\n  );<\/span>\r\n};<\/span>\r\n\r\nexport<\/span> default<\/span> Child1<\/span>;<\/span>\r\n<\/code><\/pre>\n
import<\/span> {<\/span> useContext<\/span> }<\/span> from<\/span> \"<\/span>react<\/span>\"<\/span>;<\/span>\r\nimport<\/span> {<\/span> ValueContext<\/span> }<\/span> from<\/span> \"<\/span>.\/Context.tsx<\/span>\"<\/span>;<\/span>\r\n\r\n\/\/ Child2\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8<\/span>\r\nconst<\/span> Child2<\/span> =<\/span> ()<\/span> =><\/span> {<\/span>\r\n  console<\/span>.<\/span>log<\/span>(<\/span>\"<\/span>re-rendered Child2<\/span>\"<\/span>);<\/span>\r\n  const<\/span> {<\/span> value3<\/span>,<\/span> updateValue3<\/span> }<\/span> =<\/span> useContext<\/span>(<\/span>ValueContext<\/span>);<\/span>\r\n\r\n  return <\/span>(<\/span>\r\n    <<\/span>div<\/span>><\/span>\r\n      <<\/span>h2<\/span>><\/span>Child2<\/<\/span>h2<\/span>><\/span>\r\n      <<\/span>p<\/span>><\/span>{<\/span>value3<\/span>}<\/span><\/<\/span>p<\/span>><\/span>\r\n      <<\/span>button<\/span> type<\/span>=<\/span>\"button\"<\/span> onClick<\/span>=<\/span>{<\/span>()<\/span> =><\/span> {<\/span>\r\n        updateValue3<\/span>(<\/span>value3<\/span> +<\/span> 1<\/span>);<\/span>\r\n      }<\/span>}<\/span>><\/span>+<\/<\/span>button<\/span>><\/span>\r\n    <\/<\/span>div<\/span>><\/span>\r\n  );<\/span>\r\n};<\/span>\r\n\r\nexport<\/span> default<\/span> Child2<\/span>;<\/span>\r\n<\/code><\/pre>\n
export<\/span> default<\/span> function<\/span> MyApp<\/span>()<\/span> {<\/span>\r\n  return <\/span>(<\/span>\r\n    <<\/span>ValueProvider<\/span>><\/span>\r\n      <<\/span>Parent<\/span> \/><\/span>\r\n    <\/<\/span>ValueProvider<\/span>><\/span>\r\n  );<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
\u95ee\u9898\u70b9<\/h2>\n
\u5f53value1\u88ab\u66f4\u65b0\u65f6\uff0cChild1\u3001Child2\u7ec4\u4ef6\u4e5f\u4f1a\u91cd\u65b0\u6e32\u67d3\u3002<\/h3>\n
\u5728React\u4e2d\uff0c\u5f53\u7236\u7ec4\u4ef6\u91cd\u65b0\u6e32\u67d3\u65f6\uff0c\u5b50\u7ec4\u4ef6\u4e5f\u4f1a\u91cd\u65b0\u6e32\u67d3\uff0c\u8fd9\u662fReact\u7684\u539f\u5219\u3002\u5c3d\u7ba1\u8fd9\u4e0d\u4e00\u5b9a\u662f\u95ee\u9898\uff0c\u4f46\u968f\u7740\u5e94\u7528\u89c4\u6a21\u7684\u589e\u5927\uff0c\u53ef\u80fd\u4f1a\u5bfc\u81f4\u6027\u80fd\u4e0b\u964d\u7684\u53ef\u80fd\u6027\u3002<\/p>\n
\u3010\u6587\u732e\u53c2\u8003\u3011<\/p>\n
 <\/p>\n
\u5f53value2\u548cvalue3\u66f4\u65b0\u65f6\uff0cParent\u7ec4\u4ef6\u4e5f\u4f1a\u91cd\u65b0\u6e32\u67d3\u3002<\/h3>\n
\u5f53value2\u3001value3\u7684\u503c\u66f4\u65b0\u65f6\uff0c\u53ea\u5e0c\u671b\u91cd\u65b0\u6e32\u67d3\u53d1\u751f\u66f4\u6539\u7684\u5b50\u7ec4\u4ef6\uff0c\u4f46\u4e0d\u5e0c\u671b\u53d1\u751f\u4e0d\u5fc5\u8981\u7684\u91cd\u65b0\u6e32\u67d3\uff0c\u5305\u62ec\u7236\u7ec4\u4ef6\u548c\u5144\u5f1f\u7ec4\u4ef6\u7684\u91cd\u65b0\u6e32\u67d3\u3002\u6211\u8ba4\u4e3a\u8fd9\u4e2a\u95ee\u9898\u66f4\u52a0\u91cd\u8981\u3002<\/p>\n
\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\u91cd\u65b0\u6e32\u67d3\u7684\u539f\u56e0\u662fContext\u7684\u503c\u53d1\u751f\u53d8\u5316\u65f6\uff0c\u7531\u4e8e\u4f7f\u7528\u4e86ContextAPI\u673a\u5236\uff0c\u8c03\u7528\u4e86useContext\u7684\u6240\u6709\u7ec4\u4ef6\u90fd\u4f1a\u91cd\u65b0\u6e32\u67d3\u3002\u8c22\u8c22@honey32\u7684\u6307\u6b63\u3002<\/p>\n
\u3010\u5f15\u7528\u4e8e\u516c\u5f00\u6587\u4ef6\u3011<\/p>\n
 <\/p>\n
\u5f53Provider\u7684value\u5c5e\u6027\u66f4\u6539\u65f6\uff0c\u6240\u6709\u4f5c\u4e3aProvider\u540e\u4ee3\u7684\u6d88\u8d39\u8005\u5c06\u91cd\u65b0\u6e32\u67d3\u3002\u4eceProvider\u5230\u5176\u540e\u4ee3\u6d88\u8d39\u8005\u7684\u4f20\u64ad\uff08\u5305\u62ec.contextType\u548cuseContext\uff09\u4e0d\u53d7shouldComponentUpdate\u65b9\u6cd5\u9650\u5236\uff0c\u56e0\u6b64\u5373\u4f7f\u7956\u5148\u7ec4\u4ef6\u8df3\u8fc7\u66f4\u65b0\uff0c\u6d88\u8d39\u8005\u4e5f\u4f1a\u66f4\u65b0\u3002<\/p><\/blockquote>\n
\u5728\u6240\u6709\u662fProvider\u7684\u5b50\u5b59\u7684Consumer\u4e2d\uff0c\u6bcf\u5f53Provider\u7684value prop\u53d1\u751f\u53d8\u5316\u65f6\uff0c\u5b83\u4eec\u90fd\u4f1a\u91cd\u65b0\u6e32\u67d3\u3002\u4eceProvider\u4f20\u64ad\u5230\u5176\u5b50\u5b59Consumer\u7684\u66f4\u65b0\u4e0d\u53d7shouldComponentUpdate\u65b9\u6cd5\u7684\u5f71\u54cd\uff0c\u56e0\u6b64\u5373\u4f7f\u7956\u5148\u7ec4\u4ef6\u8df3\u8fc7\u4e86\u66f4\u65b0\uff0cConsumer\u4e5f\u4f1a\u88ab\u66f4\u65b0\u3002<\/p>\n
\u5728\u8fd9\u91cc\u6240\u8bf4\u7684Provider\u7684\u4ef7\u503c\u4e3b\u5f20\u662f<\/p>\n
<<\/span>ValueContext<\/span>.<\/span>Provider<\/span> value<\/span>=<\/span>{<\/span>{<\/span>\r\n  value1<\/span>,<\/span>\r\n  updateValue1<\/span>;<\/span>\r\n  value2<\/span>,<\/span>\r\n  updateValue2<\/span>;<\/span>\r\n  value3<\/span>,<\/span>\r\n  updateValue3<\/span>;<\/span>\r\n}<\/span>}<\/span>><\/span>\r\n<\/code><\/pre>\n
\u8fd9\u6307\u7684\u662f\u8fd9\u4e00\u90e8\u5206\u3002<\/p>\n
\u6362\u8a00\u4e4b\uff0c\u4e00\u65e6\u4e0a\u4e0b\u6587\u7684\u5c5e\u6027\u503c\u88ab\u66f4\u65b0<\/p>\n
const<\/span> {<\/span> (<\/span>\u7565<\/span>)<\/span> }<\/span> =<\/span> useContext<\/span>(<\/span>ValueContext<\/span>);<\/span>\r\n<\/code><\/pre>\n
\u6240\u6709\u5305\u542b\u8fd9\u6bb5\u4ee3\u7801\u7684\u7ec4\u4ef6\u90fd\u4f1a\u88ab\u66f4\u65b0\u3002\u8003\u8651\u5230React\u7684\u8bbe\u8ba1\u601d\u60f3\uff0c\u8fd9\u662f\u4e00\u4e2a\u81ea\u7136\u800c\u7136\u7684\u7ed3\u679c\uff0c\u4f46\u8fd9\u53ef\u80fd\u4f1a\u5bfc\u81f4\u6027\u80fd\u4e0b\u964d\u3002<\/p>\n
\u3010\u53c2\u8003\u62a5\u9053\u3011<\/p>\n
 <\/p>\n
\u6539\u5584\u8ba1\u5212<\/h2>\n
\u901a\u8fc7\u4f7f\u7528React\u7684\u6807\u51c6API useMemo\uff0c\u53ef\u4ee5\u5c06\u7ec4\u4ef6\u8fd4\u56de\u7684DOM\uff08\u786e\u5207\u5730\u8bf4\u662fReact\u5143\u7d20\uff09\u8fdb\u884c\u8bb0\u5fc6\u5316\uff0c\u4ee5\u51cf\u5c11\u4e0d\u5fc5\u8981\u7684\u6e32\u67d3\u3002<\/p>\n
\u6709\u89e3\u51b3\u65b9\u6848\u7684\u7248\u672c<\/h1>\n
\u4ee3\u7801\u793a\u4f8b<\/h2>\n
import<\/span> {<\/span> useContext<\/span>,<\/span> useMemo<\/span> }<\/span> from<\/span> \"<\/span>react<\/span>\"<\/span>;<\/span>\r\nimport<\/span> {<\/span> ValueContext<\/span> }<\/span> from<\/span> \"<\/span>.\/Context.tsx<\/span>\"<\/span>;<\/span>\r\nimport<\/span> Child1<\/span> from<\/span> \"<\/span>.\/Child1<\/span>\"<\/span>;<\/span>\r\nimport<\/span> Child2<\/span> from<\/span> \"<\/span>.\/Child2<\/span>\"<\/span>;<\/span>\r\n\r\n\/\/ Parent\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8<\/span>\r\nconst<\/span> Parent<\/span> =<\/span> ()<\/span> =><\/span> {<\/span>\r\n  const<\/span> {<\/span> value1<\/span>,<\/span> updateValue1<\/span> }<\/span> =<\/span> useContext<\/span>(<\/span>ValueContext<\/span>);<\/span>\r\n\r\n  return<\/span> useMemo<\/span>(()<\/span> =><\/span> {<\/span> \/\/ React\u8981\u7d20\u3092\u30e1\u30e2\u5316<\/span>\r\n    console<\/span>.<\/span>log<\/span>(<\/span>\"<\/span>re-rendered Parent<\/span>\"<\/span>);<\/span>\r\n\r\n    return <\/span>(<\/span>\r\n      <<\/span>div<\/span>><\/span>\r\n        <<\/span>h2<\/span>><\/span>Parent<\/<\/span>h2<\/span>><\/span>\r\n        <<\/span>p<\/span>><\/span>{<\/span>value1<\/span>}<\/span><\/<\/span>p<\/span>><\/span>\r\n        <<\/span>button<\/span> type<\/span>=<\/span>\"button\"<\/span> onClick<\/span>=<\/span>{<\/span>()<\/span> =><\/span> {<\/span>\r\n          updateValue1<\/span>(<\/span>value1<\/span> +<\/span> 1<\/span>);<\/span>\r\n        }<\/span>}<\/span>><\/span>+<\/<\/span>button<\/span>><\/span>\r\n        <<\/span>Child1<\/span> \/><\/span>\r\n        <<\/span>Child2<\/span> \/><\/span>\r\n      <\/<\/span>div<\/span>><\/span>\r\n    );<\/span>\r\n  },<\/span> [<\/span>value1<\/span>]);<\/span> \/\/ value1\u304c\u66f4\u65b0\u3055\u308c\u305f\u3068\u304d\u306e\u307f\u518d\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0<\/span>\r\n};<\/span>\r\n\r\nexport<\/span> default<\/span> Parent<\/span>;<\/span>\r\n<\/code><\/pre>\n
import<\/span> {<\/span> useContext<\/span>,<\/span> useMemo<\/span> }<\/span> from<\/span> \"<\/span>react<\/span>\"<\/span>;<\/span>\r\nimport<\/span> {<\/span> ValueContext<\/span> }<\/span> from<\/span> \"<\/span>.\/Context.tsx<\/span>\"<\/span>;<\/span>\r\n\r\n\/\/ Child1\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8<\/span>\r\nconst<\/span> Child1<\/span> =<\/span> ()<\/span> =><\/span> {<\/span>\r\n  const<\/span> {<\/span> value2<\/span>,<\/span> updateValue2<\/span> }<\/span> =<\/span> useContext<\/span>(<\/span>ValueContext<\/span>);<\/span>\r\n\r\n  return<\/span> useMemo<\/span>(()<\/span> =><\/span> {<\/span> \/\/ React\u8981\u7d20\u3092\u30e1\u30e2\u5316<\/span>\r\n    console<\/span>.<\/span>log<\/span>(<\/span>\"<\/span>re-rendered Child1<\/span>\"<\/span>);<\/span>\r\n\r\n    return <\/span>(<\/span>\r\n      <<\/span>div<\/span>><\/span>\r\n        <<\/span>h2<\/span>><\/span>Child1<\/<\/span>h2<\/span>><\/span>\r\n        <<\/span>p<\/span>><\/span>value2: {<\/span>value2<\/span>}<\/span><\/<\/span>p<\/span>><\/span>\r\n        <<\/span>button<\/span> type<\/span>=<\/span>\"button\"<\/span> onClick<\/span>=<\/span>{<\/span>()<\/span> =><\/span> {<\/span>\r\n          updateValue2<\/span>(<\/span>value2<\/span> +<\/span> 1<\/span>);<\/span>\r\n        }<\/span>}<\/span>><\/span>+<\/<\/span>button<\/span>><\/span>\r\n      <\/<\/span>div<\/span>><\/span>\r\n    );<\/span>\r\n  },<\/span> [<\/span>value2<\/span>]);<\/span> \/\/ value2\u304c\u66f4\u65b0\u3055\u308c\u305f\u3068\u304d\u306e\u307f\u518d\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0<\/span>\r\n};<\/span>\r\n\r\nexport<\/span> default<\/span> Child1<\/span>;<\/span>\r\n<\/code><\/pre>\n
import<\/span> {<\/span> useContext<\/span>,<\/span> useMemo<\/span> }<\/span> from<\/span> \"<\/span>react<\/span>\"<\/span>;<\/span>\r\nimport<\/span> {<\/span> ValueContext<\/span> }<\/span> from<\/span> \"<\/span>.\/Context.tsx<\/span>\"<\/span>;<\/span>\r\n\r\n\/\/ Child2\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8<\/span>\r\nconst<\/span> Child2<\/span> =<\/span> ()<\/span> =><\/span> {<\/span>\r\n  const<\/span> {<\/span> value3<\/span>,<\/span> updateValue3<\/span> }<\/span> =<\/span> useContext<\/span>(<\/span>ValueContext<\/span>);<\/span>\r\n\r\n  return<\/span> useMemo<\/span>(()<\/span> =><\/span> {<\/span> \/\/ React\u8981\u7d20\u3092\u30e1\u30e2\u5316<\/span>\r\n    console<\/span>.<\/span>log<\/span>(<\/span>\"<\/span>re-rendered Child2<\/span>\"<\/span>);<\/span>\r\n\r\n    return <\/span>(<\/span>\r\n      <<\/span>div<\/span>><\/span>\r\n        <<\/span>h2<\/span>><\/span>Child2<\/<\/span>h2<\/span>><\/span>\r\n        <<\/span>p<\/span>><\/span>value3: {<\/span>value3<\/span>}<\/span><\/<\/span>p<\/span>><\/span>\r\n        <<\/span>button<\/span> type<\/span>=<\/span>\"button\"<\/span> onClick<\/span>=<\/span>{<\/span>()<\/span> =><\/span> {<\/span>\r\n          updateValue3<\/span>(<\/span>value3<\/span> +<\/span> 1<\/span>);<\/span>\r\n        }<\/span>}<\/span>><\/span>+<\/<\/span>button<\/span>><\/span>\r\n      <\/<\/span>div<\/span>><\/span>\r\n    );<\/span>\r\n  },<\/span> [<\/span>value3<\/span>]);<\/span> \/\/ value3\u304c\u66f4\u65b0\u3055\u308c\u305f\u3068\u304d\u306e\u307f\u518d\u30ec\u30f3\u30c0\u30ea\u30f3\u30b0<\/span>\r\n};<\/span>\r\n\r\nexport<\/span> default<\/span> Child2<\/span>;<\/span>\r\n<\/code><\/pre>\n
\u6267\u884c\u7ed3\u679c<\/h2>\n
\u4ec5\u91cd\u65b0\u6e32\u67d3\u4e86\u53d1\u751f\u53d8\u5316\u7684\u7ec4\u4ef6\u3002\u51c6\u786e\u5730\u8bf4\uff0c\u7ec4\u4ef6\u51fd\u6570\u672c\u8eab\u4f1a\u6267\u884c\uff0c\u4f46\u53ea\u8981useMemo\u7684\u7b2c2\u4e2a\u53c2\u6570\u503c\u4e0d\u53d8\uff0c\u5c31\u4e0d\u4f1a\u53d1\u751f\u91cd\u65b0\u6e32\u67d3\u7684\u8ba1\u7b97\uff0c\u56e0\u6b64\u53ef\u4ee5\u63d0\u9ad8\u6027\u80fd\u3002<\/p>\n
\u6700\u540e<\/h1>\n
\u6211\u5bf9React\u8fd8\u662f\u4e00\u4e2a\u521d\u5b66\u8005\uff0c\u6240\u4ee5\u5982\u679c\u6709\u4efb\u4f55\u9519\u8bef\u6216\u9700\u8981\u4fee\u6539\u7684\u5730\u65b9\uff0c\u8bf7\u52a1\u5fc5\u5728\u8bc4\u8bba\u4e2d\u6307\u51fa\uff0c\u8c22\u8c22\u60a8\u7684\u5e2e\u52a9\u3002<\/p>\n
\u76f8\u5173\u6587\u7ae0<\/h2>\n
 <\/p>\n","protected":false},"excerpt":{"rendered":"
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