{"id":39602,"date":"2023-02-02T19:09:38","date_gmt":"2024-02-04T04:54:36","guid":{"rendered":"https:\/\/www.silicloud.com\/zh\/blog\/%e5%ad%a6%e4%b9%a0angular%e7%9a%84asyncpipe\/"},"modified":"2024-04-29T12:48:17","modified_gmt":"2024-04-29T04:48:17","slug":"%e5%ad%a6%e4%b9%a0angular%e7%9a%84asyncpipe","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/zh\/blog\/%e5%ad%a6%e4%b9%a0angular%e7%9a%84asyncpipe\/","title":{"rendered":"\u5b66\u4e60Angular\u7684AsyncPipe"},"content":{"rendered":"

\u8fd9\u7bc7\u6587\u7ae0\u662f2022\u5e74Angular\u5723\u8bde\u65e5\u5386\u4e0a\u7b2c20\u5929\u7684\u6587\u7ae0\u3002
\n\u8fd9\u662f\u5173\u4e8e\u5b66\u4e60AsyncPipe\u7684\u8bb0\u5f55\u3002<\/p>\n

\u5f02\u6b65\u7ba1\u9053\u662f\u4ec0\u4e48\uff1f<\/h1>\n

\u9996\u5148\uff0c\u6211\u5011\u5148\u78ba\u8a8d\u5b98\u65b9\u7db2\u9801\u3002<\/p>\n

 <\/p>\n

\u5f02\u6b65\u7ba1\u9053\u8ba2\u9605 Observable \u6216 Promise\uff0c\u5e76\u8fd4\u56de\u5176\u5df2\u53d1\u51fa\u7684\u6700\u65b0\u503c\u3002\u5f53\u6709\u65b0\u503c\u88ab\u53d1\u51fa\u65f6\uff0c\u5f02\u6b65\u7ba1\u9053\u6807\u8bb0\u8be5\u7ec4\u4ef6\u4ee5\u8fdb\u884c\u53d8\u66f4\u68c0\u67e5\u3002\u5f53\u7ec4\u4ef6\u88ab\u9500\u6bc1\u65f6\uff0c\u5f02\u6b65\u7ba1\u9053\u4f1a\u81ea\u52a8\u53d6\u6d88\u8ba2\u9605\uff0c\u4ee5\u907f\u514d\u6f5c\u5728\u7684\u5185\u5b58\u6cc4\u6f0f\u3002\u5f53\u8868\u8fbe\u5f0f\u7684\u5f15\u7528\u53d1\u751f\u53d8\u5316\u65f6\uff0c\u5f02\u6b65\u7ba1\u9053\u4f1a\u81ea\u52a8\u53d6\u6d88\u8ba2\u9605\u65e7\u7684 Observable \u6216 Promise\uff0c\u5e76\u8ba2\u9605\u65b0\u7684\u3002<\/p><\/blockquote>\n

    \n
  1. \n
      \u901a\u8fc7\u8ba2\u9605Observable\uff08\u6216Promise\uff09\uff0c\u8fd4\u56de\u6700\u65b0\u7684\u503c\u3002<\/ol>\n<\/li>\n<\/ol>\n

      \u5f53\u7ec4\u4ef6\u88ab\u9500\u6bc1\u65f6\uff0cAsyncPipe\u4f1a\u81ea\u52a8\u53d6\u6d88\u8ba2\u9605\u3002
      \n\u5f53\u5f15\u7528\u7684\u8868\u8fbe\u5f0f\u53d1\u751f\u53d8\u5316\u65f6\uff0cAsyncPipe\u4f1a\u81ea\u52a8\u53d6\u6d88\u8ba2\u9605\u65e7\u7684Observable\u5e76\u8ba2\u9605\u65b0\u7684Observable\u3002<\/p>\n

      \n

      \u4f7f\u7528AsyncPipe\u7684\u597d\u5904\u662f\u4ec0\u4e48\uff1f<\/p>\n

        \n
      • \n
          \u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u3067\u306e\u8cfc\u8aad\u89e3\u9664\u306b\u95a2\u3059\u308b\u30b3\u30fc\u30c9\u3092\u66f8\u304b\u306a\u304f\u3066\u826f\u3044<\/ul>\n<\/li>\n<\/ul>\n

          \u8cfc\u8aad\u89e3\u9664\u5fd8\u308c\u3092\u5fc3\u914d\u3092\u3057\u306a\u304f\u3066\u826f\u3044\uff08\u8cfc\u8aad\u89e3\u9664\u5fd8\u308c\u306f\u30e1\u30e2\u30ea\u30ea\u30fc\u30af\u3092\u5f15\u304d\u8d77\u3053\u3059\uff09
          \n\u30b3\u30f3\u30dd\u30fc\u30cd\u30f3\u30c8\u306e\u30b3\u30fc\u30c9\u91cf\u304c\u6e1b\u308a\u30b9\u30c3\u30ad\u30ea\u3059\u308b<\/p>\n

          Observable\u306e\u521d\u671f\u5316\u3092\u30b3\u30f3\u30b9\u30c8\u30e9\u30af\u30bf\u3067\u5b8c\u7d50\u3055\u305b\u308b\u3053\u3068\u304c\u3067\u304d\u308b
          \nreadonly\u306b\u3067\u304d\u308b<\/p>\n

           <\/p>\n

          \u5c31\u7b2c2.3\u4e2a\u539f\u56e0\u800c\u8a00\uff0c\u4f5c\u4e3a\u4e00\u4e2a\u521d\u5b66\u8005\uff0c\u6211\u5e76\u6ca1\u6709\u592a\u591a\u4f53\u4f1a\u5230\u5176\u4e2d\u7684\u4e50\u8da3\uff0c\u6240\u4ee5\u5982\u679c\u627e\u5230\u4e00\u4e2a\u597d\u7684\u4f8b\u5b50\uff0c\u6211\u4f1a\u518d\u6b21\u5199\u4e0b\u6765\u3002
          \n\u5c31\u7b2c1\u4e2a\u539f\u56e0\u800c\u8a00\uff0c\u901a\u8fc7\u6bd4\u8f83\u5f15\u5165 AsyncPipe \u524d\u540e\u7684\u4ee3\u7801\uff0c\u4e00\u76ee\u4e86\u7136\u3002<\/p>\n

          import<\/span> {<\/span> Component<\/span>,<\/span> OnDestroy<\/span>,<\/span> OnInit<\/span> }<\/span> from<\/span> '<\/span>@angular\/core<\/span>'<\/span>;<\/span>\r\nimport<\/span> {<\/span> UserListService<\/span> }<\/span> from<\/span> '<\/span>..\/user-list.service<\/span>'<\/span>;<\/span>\r\nimport<\/span> {<\/span> Subject<\/span> }<\/span> from<\/span> '<\/span>rxjs<\/span>'<\/span>;<\/span>\r\nimport<\/span> {<\/span> takeUntil<\/span> }<\/span> from<\/span> '<\/span>rxjs\/operators<\/span>'<\/span>;<\/span>\r\n\r\n@<\/span>Component<\/span>({<\/span>\r\n  selector<\/span>:<\/span> '<\/span>user-list<\/span>'<\/span>,<\/span>\r\n  template<\/span>:<\/span> `\r\n    <ul>\r\n        <li *ngFor=\"let user of users\">\r\n    \t\t{{ user.id }} {{ user.first_name }} {{ user.last_name }}\r\n    \t<\/li>\r\n    <\/ul>\r\n  `<\/span>,<\/span>\r\n})<\/span>\r\nexport<\/span> class<\/span> UserListComponent<\/span> implements<\/span> OnDestroy<\/span>,<\/span> OnInit<\/span> {<\/span>\r\n  private<\/span> _onDestroy<\/span> =<\/span> new<\/span> Subject<\/span><<\/span>void<\/span>><\/span>();<\/span>\r\n  users<\/span>:<\/span> User<\/span>[];<\/span>\r\n\r\n  constructor<\/span>(<\/span>private<\/span> userListService<\/span>:<\/span> UserListService<\/span>)<\/span> {<\/span> }<\/span>\r\n\r\n  ngOnInit<\/span>()<\/span> {<\/span>\r\n    this<\/span>.<\/span>userListService<\/span>.<\/span>getUsers<\/span>()<\/span>\r\n      .<\/span>pipe<\/span>(<\/span>takeUntil<\/span>(<\/span>this<\/span>.<\/span>onDestroy<\/span>))<\/span>\r\n      .<\/span>subscribe<\/span>(<\/span>users<\/span> =><\/span> {<\/span>\r\n        this<\/span>.<\/span>users<\/span> =<\/span> users<\/span>;<\/span>\r\n      });<\/span>\r\n  }<\/span>\r\n\r\n  ngOnDestroy<\/span>()<\/span> {<\/span>\r\n    this<\/span>.<\/span>_onDestroy<\/span>.<\/span>next<\/span>(<\/span>null<\/span>);<\/span>\r\n  }<\/span>\r\n\r\n}<\/span>\r\n<\/code><\/pre>\n
          import<\/span> {<\/span> Component<\/span>,<\/span> OnInit<\/span> }<\/span> from<\/span> '<\/span>@angular\/core<\/span>'<\/span>;<\/span>\r\nimport<\/span> {<\/span> UserListService<\/span> }<\/span> from<\/span> '<\/span>..\/user-list.service<\/span>'<\/span>;<\/span>\r\n\r\n@<\/span>Component<\/span>({<\/span>\r\n  selector<\/span>:<\/span> '<\/span>user-list<\/span>'<\/span>,<\/span>\r\n  template<\/span>:<\/span> `\r\n    <ul>\r\n        <li *ngFor=\"let user of users$ | async\">\r\n    \t\t{{ user.id }} {{ user.first_name }} {{ user.last_name }}\r\n    \t<\/li>\r\n    <\/ul>\r\n  `<\/span>,<\/span>\r\n})<\/span>\r\nexport<\/span> class<\/span> UserListComponent<\/span> implements<\/span> OnInit<\/span> {<\/span> \/\/ \u3060\u3044\u3076\u30b9\u30c3\u30ad\u30ea\u3057\u305f<\/span>\r\n  readonly<\/span> users$<\/span>:<\/span> Observavle<\/span><<\/span>User<\/span>[]<\/span>><\/span>;<\/span>\r\n\r\n  constructor<\/span>(<\/span>private<\/span> userListService<\/span>:<\/span> UserListService<\/span>)<\/span> {<\/span>\r\n    this<\/span>.<\/span>users$<\/span> =<\/span> this<\/span>.<\/span>userListService<\/span>.<\/span>getUsers<\/span>();<\/span>\r\n  }<\/span>\r\n\r\n  ngOnInit<\/span>()<\/span> {<\/span>\r\n  }<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
          \u5728\u7ec4\u4ef6\u5185\uff0c\u6709\u5173\u53d6\u6d88\u8ba2\u9605\u7684\u63cf\u8ff0\u5b8c\u5168\u6d88\u5931\u4e86\uff0c\u611f\u89c9\u975e\u5e38\u6e05\u723d\u3002<\/p>\n
          \u7136\u800c\uff0c\u5f02\u6b65\u7ba1\u9053\u4e5f\u6709\u4ee4\u4eba\u56f0\u6270\u7684\u5730\u65b9\u3002<\/p>\n
          \u521d\u59cb\u503c\u4e3a\u7a7a\u95ee\u9898 zh\u00ed<\/h1>\n
           <\/p>\n
          \u5728\u4f7f\u7528AsyncPipe\u65f6\uff0c\u5c3d\u7ba1\u6d41(Stream)\u4e2d\u7edd\u5bf9\u4e0d\u4f1a\u51fa\u73b0null\uff0c\u4f46\u5176\u5b50\u7ec4\u4ef6\u5374\u4e0d\u5f97\u4e0d\u5173\u6ce8null\u3002<\/p><\/blockquote>\n
          \u5047\u8bbe\u5728\u4ee5\u4e0b\u60c5\u51b5\u4e0b\uff0c\u4f1a\u5728\u7f16\u8bd1\u65f6\u5f15\u53d1\u9519\u8bef\u3002<\/p>\n
          import<\/span> {<\/span> Component<\/span>,<\/span> OnInit<\/span> }<\/span> from<\/span> '<\/span>@angular\/core<\/span>'<\/span>;<\/span>\r\nimport<\/span> {<\/span> UserListService<\/span> }<\/span> from<\/span> '<\/span>..\/user-list.service<\/span>'<\/span>;<\/span>\r\n\r\n@<\/span>Component<\/span>({<\/span>\r\n  selector<\/span>:<\/span> '<\/span>app-root<\/span>'<\/span>,<\/span>\r\n  template<\/span>:<\/span> `<user-list [users]=\"users$ | async\"><\/user-list>`<\/span>,<\/span>\r\n})<\/span>\r\nexport<\/span> class<\/span> AppComponent<\/span> implements<\/span> OnInit<\/span> {<\/span>\r\n  readonly<\/span> users$<\/span>:<\/span> Observavle<\/span><<\/span>User<\/span>[]<\/span>><\/span>;<\/span>\r\n\r\n  constructor<\/span>(<\/span>private<\/span> userListService<\/span>:<\/span> UserListService<\/span>)<\/span> {<\/span>\r\n    this<\/span>.<\/span>users$<\/span> =<\/span> this<\/span>.<\/span>userListService<\/span>.<\/span>getUsers<\/span>();<\/span>\r\n  }<\/span>\r\n\r\n  ngOnInit<\/span>()<\/span> {<\/span>\r\n  }<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
          @<\/span>Component<\/span>({<\/span>\r\n  selector<\/span>:<\/span> '<\/span>user-list<\/span>'<\/span>,<\/span>\r\n  template<\/span>:<\/span> `\r\n    <ul>\r\n        <li *ngFor=\"let user of users\">\r\n    \t\t{{ user.id }} {{ user.first_name }} {{ user.last_name }}\r\n    \t<\/li>\r\n    <\/ul>\r\n  `<\/span>,<\/span>\r\n})<\/span>\r\nexport<\/span> class<\/span> UserListComponent<\/span> implements<\/span> OnInit<\/span> {<\/span>\r\n  @<\/span>Input<\/span>()<\/span> users<\/span>:<\/span> User<\/span>[];<\/span>\r\n\r\n  constructor<\/span>()<\/span> {<\/span> }<\/span>\r\n\r\n  ngOnInit<\/span>()<\/span> {<\/span>\r\n  }<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
          Type 'null' is not assignable to type 'User[]'.\r\n\r\n<\/span>1 <user-list [users]=\"users$<\/span> | async\"><\/user-list>\r\n<\/span>              ~~~~~\r\n<\/span><\/code><\/pre>\n
          \u5982\u679c\u5c06null\u653e\u5165User[]\u7c7b\u578b\u7684users\u53d8\u91cf\u4e2d\u5219\u4e0d\u884c\uff01\uff01
          \n\u5982\u4e0b\u6240\u793a\uff0cUserListService\u7684getUsers()\u65b9\u6cd5\u4e0d\u4f1a\u8fd4\u56denull\u3002<\/p>\n
          @<\/span>Injectable<\/span>({<\/span> providedIn<\/span>:<\/span> '<\/span>root<\/span>'<\/span> })<\/span>\r\nexport<\/span> class<\/span> UserListService<\/span> {<\/span>\r\n\r\n  constructor<\/span>(<\/span>private<\/span> http<\/span>:<\/span> HttpClient<\/span>)<\/span> {<\/span> }<\/span>\r\n\r\n  getUsers<\/span>():<\/span> Observable<\/span><<\/span>User<\/span>[]<\/span>><\/span> {<\/span>\r\n    return<\/span> this<\/span>.<\/span>http<\/span>\r\n      .<\/span>get<\/span><<\/span>{<\/span> data<\/span>:<\/span> User<\/span>[]<\/span> }<\/span>><\/span>(<\/span>\"<\/span>https:\/\/reqres.in\/api\/users<\/span>\"<\/span>)<\/span>\r\n      .<\/span>pipe<\/span>(<\/span>\r\n        map<\/span>(<\/span>resp<\/span> =><\/span> resp<\/span>.<\/span>data<\/span>)<\/span>\r\n      );<\/span>\r\n  }<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
          \u5c3d\u7ba1\u7528\u6237\u4e3a\u7a7a\u4f46\u4ecd\u7136\u8fdb\u5165\u4e86null\u7684\u539f\u56e0\u5728\u4e8eAsyncPipe\u7684\u5b9e\u73b0\u3002<\/p>\n
           <\/p>\n
          \u8fd9\u7bc7\u6587\u7ae0\u8be6\u7ec6\u89e3\u91ca\u4e86\uff0c\u4f46\u56e0\u4e3a\u8fd9\u7bc7\u6587\u7ae0\u662f\u57282020\u5e74\u5199\u7684\uff0c\u4ee3\u7801\u6709\u4e9b\u53d8\u52a8\uff0c\u6240\u4ee5\u6211\u4f1a\u518d\u6b21\u786e\u8ba4\u3002
          \n\uff08\u6211\u590d\u5236\u4e86AsyncPipe\u5e76\u521b\u5efa\u4e86\u4e00\u4e2a\u540d\u4e3aMyAsyncPipe\u7684\u7ba1\u9053\uff0c\u7136\u540e\u5feb\u4e50\u5730\u52a0\u5165\u4e86console.log()\u3002?\uff09<\/p>\n
          transform()\u51fd\u6570\u662f\u5173\u952e\u4ee3\u7801\u3002<\/p>\n
          @<\/span>Pipe<\/span>({<\/span>\r\n  name<\/span>:<\/span> '<\/span>async<\/span>'<\/span>,<\/span>\r\n  pure<\/span>:<\/span> false<\/span>,<\/span>\r\n  standalone<\/span>:<\/span> true<\/span>,<\/span>\r\n})<\/span>\r\nexport<\/span> class<\/span> AsyncPipe<\/span> implements<\/span> OnDestroy<\/span>,<\/span> PipeTransform<\/span> {<\/span>\r\n  private<\/span> _latestValue<\/span>:<\/span> any<\/span> =<\/span> null<\/span>;<\/span> \/\/<- \u30b3\u30a4\u30c4\u304c\u554f\u984c<\/span>\r\n                              ~~~~<\/span> \r\n  private<\/span> _obj<\/span>:<\/span> Subscribable<\/span><<\/span>any<\/span>>|<\/span>Promise<\/span><<\/span>any<\/span>>|<\/span>EventEmitter<\/span><<\/span>any<\/span>>|<\/span>null<\/span> =<\/span> null<\/span>;<\/span>\r\n  \/\/ \u7565<\/span>\r\n\r\n  transform<\/span><<\/span>T<\/span>><\/span>(<\/span>obj<\/span>:<\/span> Observable<\/span><<\/span>T<\/span>>|<\/span>Subscribable<\/span><<\/span>T<\/span>>|<\/span>Promise<\/span><<\/span>T<\/span>>|<\/span>null<\/span>|<\/span>undefined<\/span>):<\/span> T<\/span>|<\/span>null<\/span> {<\/span>\r\n    \/\/ \u2460AsyncPipe\u306b\u521d\u3081\u3066Observable\u304c\u6e21\u3055\u308c\u305f\u3068\u304d<\/span>\r\n    if <\/span>(<\/span>!<\/span>this<\/span>.<\/span>_obj<\/span>)<\/span> {<\/span>\r\n      if <\/span>(<\/span>obj<\/span>)<\/span> {<\/span>\r\n        this<\/span>.<\/span>_subscribe<\/span>(<\/span>obj<\/span>);<\/span>\r\n      }<\/span>\r\n      return<\/span> this<\/span>.<\/span>_latestValue<\/span>;<\/span> \r\n    }<\/span>\r\n    \/\/ \uff08obj\u306e\u53c2\u7167\u304c\u5909\u308f\u3063\u305f\u6642\uff08\u5225\u306eObservable\u304c\u6e21\u3055\u308c\u305f\u6642\u3001\u4eca\u56de\u306e\u8a71\u3092\u3059\u308b\u4e0a\u3067\u306f\u91cd\u8981\u3067\u306f\u306a\u3044\uff09\uff09<\/span>\r\n    if <\/span>(<\/span>obj<\/span> !==<\/span> this<\/span>.<\/span>_obj<\/span>)<\/span> {<\/span>\r\n      this<\/span>.<\/span>_dispose<\/span>();<\/span>\r\n      return<\/span> this<\/span>.<\/span>transform<\/span>(<\/span>obj<\/span>);<\/span>\r\n    }<\/span>\r\n\r\n    return<\/span> this<\/span>.<\/span>_latestValue<\/span>;<\/span>\r\n  }<\/span>\r\n  \/\/ \u7565<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
          \u8fd9\u662f\u5728transform\uff08\uff09\u51fd\u6570\u5185\u8c03\u7528\u7684\u91cd\u8981\u4ee3\u7801\u3002<\/p>\n
          class<\/span> SubscribableStrategy<\/span> implements<\/span> SubscriptionStrategy<\/span> {<\/span>\r\n  createSubscription<\/span>(<\/span>async<\/span>:<\/span> Subscribable<\/span><<\/span>any<\/span>><\/span>,<\/span> updateLatestValue<\/span>:<\/span> any<\/span>):<\/span> Unsubscribable<\/span> {<\/span>\r\n    return<\/span> async<\/span>.<\/span>subscribe<\/span>({<\/span>\r\n      next<\/span>:<\/span> updateLatestValue<\/span>,<\/span>\r\n      error<\/span>:<\/span> (<\/span>e<\/span>:<\/span> any<\/span>)<\/span> =><\/span> {<\/span>\r\n        throw<\/span> e<\/span>;<\/span>\r\n      }<\/span>\r\n    });<\/span>\r\n  }<\/span>\r\n  \/\/ \u7565<\/span>\r\n}<\/span>\r\n\r\nprivate<\/span> _subscribe<\/span>(<\/span>obj<\/span>:<\/span> Subscribable<\/span><<\/span>any<\/span>>|<\/span>Promise<\/span><<\/span>any<\/span>>|<\/span>EventEmitter<\/span><<\/span>any<\/span>><\/span>):<\/span> void<\/span> {<\/span>\r\n  this<\/span>.<\/span>_obj<\/span> =<\/span> obj<\/span>;<\/span>\r\n  this<\/span>.<\/span>_strategy<\/span> =<\/span> this<\/span>.<\/span>_selectStrategy<\/span>(<\/span>obj<\/span>);<\/span>\r\n  this<\/span>.<\/span>_subscription<\/span> =<\/span> this<\/span>.<\/span>_strategy<\/span>.<\/span>createSubscription<\/span>(<\/span>\r\n    obj<\/span>,<\/span> (<\/span>value<\/span>:<\/span> Object<\/span>)<\/span> =><\/span> this<\/span>.<\/span>_updateLatestValue<\/span>(<\/span>obj<\/span>,<\/span> value<\/span>));<\/span>\r\n}<\/span>\r\n\r\nprivate<\/span> _updateLatestValue<\/span>(<\/span>async<\/span>:<\/span> any<\/span>,<\/span> value<\/span>:<\/span> Object<\/span>):<\/span> void<\/span> {<\/span>\r\n  if <\/span>(<\/span>async<\/span> ===<\/span> this<\/span>.<\/span>_obj<\/span>)<\/span> {<\/span>\r\n    this<\/span>.<\/span>_latestValue<\/span> =<\/span> value<\/span>;<\/span>\r\n    this<\/span>.<\/span>_ref<\/span>!<\/span>.<\/span>markForCheck<\/span>();<\/span>\r\n  }<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
          \u5982\u679c\u5c06getUsers()\u8fd4\u56de\u7684Observable\u8868\u793a\u4e3a?\uff0c
          \n\u5927\u81f4\u6d41\u7a0b\u5982\u4e0b\u3002<\/p>\n
          \n
          No\u51e6\u7406_obj_latestValue1AsyncPipe<\/code>\u306b?\uff08=obj<\/code>\uff09\u304c\u6e21\u3055\u308c\u308bnullnull2transform()<\/code>\u304c\u547c\u3070\u308c\u308bnullnull3_obj===null<\/code> \u306a\u306e\u3067\u2460\u306eif\u6587\u306e\u5185\u90e8\u3078nullnull4_subscribe()<\/code>\u304c\u547c\u3070\u308c\u308bnullnull5this._obj<\/code>\u3092\u4e0a\u66f8\u304d?null6createSubscription<\/code>\u3067?\u306e\u8cfc\u8aad\u3092\u958b\u59cb?null7return this._latestValue<\/code>?null<\/div>\n<\/div>\n
          \u76ee\u524d\u4e3a\u6b62\uff0c_latestValue\u4ecd\u7136\u4fdd\u6301\u521d\u59cb\u503cnull\uff0c\u672a\u88ab\u8986\u76d6\uff0c\u56e0\u6b64return this._latestValue\u5c06\u8fd4\u56denull\u3002\u8fd9\u5c31\u662f\u6240\u8c13\u7684”AsyncPipe\u521d\u59cb\u503cnull\u95ee\u9898”\u3002<\/p>\n
          \u600e\u4e48\u6253\u5012\u5b83<\/h1>\n
          \u53ea\u9700\u8981\u4e00\u4e2a\u9009\u9879\uff1a\u6839\u636e\u89c6\u9891\u6216\u6587\u7ae0\u4e2d\u6240\u793a\uff0c\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u4f7f\u7528\u8bf8\u5982*ngIf\u6216*ngFor\u7b49\u5ffd\u7565\u7a7a\u503c\u7684\u6307\u4ee4\u6765\u5b9e\u73b0\u51fb\u8d25\u5b83\u3002<\/p>\n
          import<\/span> {<\/span> Component<\/span>,<\/span> OnInit<\/span> }<\/span> from<\/span> '<\/span>@angular\/core<\/span>'<\/span>;<\/span>\r\nimport<\/span> {<\/span> UserListService<\/span> }<\/span> from<\/span> '<\/span>..\/user-list.service<\/span>'<\/span>;<\/span>\r\n\r\n@<\/span>Component<\/span>({<\/span>\r\n  selector<\/span>:<\/span> '<\/span>app-root<\/span>'<\/span>,<\/span>\r\n  template<\/span>:<\/span> `\r\n    <ng-container *ngIf=\"users$ | async as users\">\r\n        <user-list [users]=\"users\"><\/user-list>\r\n    <\/ng-container>\r\n  `<\/span>,<\/span>\r\n})<\/span>\r\nexport<\/span> class<\/span> AppComponent<\/span> implements<\/span> OnInit<\/span> {<\/span>\r\n  readonly<\/span> users$<\/span>:<\/span> Observavle<\/span><<\/span>User<\/span>[]<\/span>><\/span>;<\/span>\r\n\r\n  constructor<\/span>(<\/span>private<\/span> userListService<\/span>:<\/span> UserListService<\/span>)<\/span> {<\/span>\r\n    this<\/span>.<\/span>users$<\/span> =<\/span> this<\/span>.<\/span>userListService<\/span>.<\/span>getUsers<\/span>();<\/span>\r\n  }<\/span>\r\n\r\n  ngOnInit<\/span>()<\/span> {<\/span>\r\n  }<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
          \u5e94\u8be5\u59cb\u7ec8\u901a\u8fc7Null\u5b89\u5168\u7684NgIf\u6216NgFor\u6765\u4f7f\u7528AsyncPipe\u3002<\/p><\/blockquote>\n
          \u8fd9\u5c31\u662f\u7ed3\u8bba\u3002
          \n\u6b64\u5916\uff0c\u5728\u89c6\u9891\u548c\u4e0b\u9762\u7684\u6587\u7ae0\u4e2d\uff0c\u8fd8\u4ecb\u7ecd\u4e86\u4e00\u79cd\u79f0\u4e3aSingle State Stream\u7684\u65b9\u6cd5\uff0c\u53ef\u4ee5\u5c06\u591a\u4e2a\u5f02\u6b65\u503c\u6346\u7ed1\u6210\u5355\u4e2a\u6d41\u5e76\u8fdb\u884c\u5feb\u7167\u3002\u8bf7\u52a1\u5fc5\u53bb\u770b\u4e00\u770b\u3002<\/p>\n
           <\/p>\n
          \n
          \u987a\u4fbf\u63d0\u4e00\u53e5\uff0c\u5728\u89c6\u9891\u91cc<\/p>\n
          \u5373\u4f7f\u662f\u50cfBehaviorSubject\u4e00\u6837\uff0c\u5df2\u786e\u5b9a\u5728\u8ba2\u9605\u65f6\u6d41\u52a8\u503c\u7684\u6d41\uff0c\u4e5f\u53ef\u80fd\u4f1a\u51fa\u73b0null\u503c\u3002<\/p><\/blockquote>\n
          \u56e0\u4e3a\u60a8\u8bf4\u8fc7\uff0c\u6240\u4ee5\u6211\u4e5f\u8fdb\u884c\u4e86\u8c03\u67e5\u3002<\/p>\n
          import<\/span> {<\/span> Component<\/span>,<\/span> OnInit<\/span> }<\/span> from<\/span> '<\/span>@angular\/core<\/span>'<\/span>;<\/span>\r\nimport<\/span> {<\/span> UserListService<\/span> }<\/span> from<\/span> '<\/span>..\/user-list.service<\/span>'<\/span>;<\/span>\r\n\r\n@<\/span>Component<\/span>({<\/span>\r\n  selector<\/span>:<\/span> '<\/span>app-root<\/span>'<\/span>,<\/span>\r\n  template<\/span>:<\/span> `<user-list [users]=\"users$ | async\"><\/user-list>`<\/span>,<\/span>\r\n})<\/span>\r\nexport<\/span> class<\/span> AppComponent<\/span> implements<\/span> OnInit<\/span> {<\/span>\r\n  readonly<\/span> users$<\/span>:<\/span> Observavle<\/span><<\/span>User<\/span>[]<\/span>><\/span>;<\/span>\r\n\r\n  constructor<\/span>(<\/span>private<\/span> userListService<\/span>:<\/span> UserListService<\/span>)<\/span> {<\/span>\r\n- <\/span>  this<\/span>.<\/span>users$<\/span> =<\/span> this<\/span>.<\/span>userListService<\/span>.<\/span>getUsers<\/span>();<\/span>\r\n<\/span>+ <\/span>  this<\/span>.<\/span>users$<\/span> =<\/span> this<\/span>.<\/span>userListService<\/span>.<\/span>users$<\/span>;<\/span>\r\n<\/span>  }<\/span>\r\n\r\n  ngOnInit<\/span>()<\/span> {<\/span>\r\n  }<\/span>\r\n}<\/span>\r\n<\/code><\/pre>\n
          @<\/span>Injectable<\/span>({<\/span> providedIn<\/span>:<\/span> '<\/span>root<\/span>'<\/span> })<\/span>\r\nexport<\/span> class<\/span> UserListService<\/span> {<\/span>\r\n\r\n+ <\/span>private<\/span> _usersSubject<\/span> =<\/span> new<\/span> BehaviorSubject<\/span><<\/span>User<\/span>[]<\/span>><\/span>([]);<\/span> \/\/ <-\u8cfc\u8aad\u3068\u540c\u6642\u306b[]\u304c\u6d41\u308c\u308b<\/span>\r\n<\/span>\r\n+ <\/span>get<\/span> users<\/span>$<\/span>()<\/span> {<\/span>\r\n<\/span>+ <\/span>  return<\/span> this<\/span>.<\/span>_usersSubject<\/span>.<\/span>asObservable<\/span>()<\/span> \r\n<\/span>+ <\/span>}<\/span>\r\n<\/span>\r\n  constructor<\/span>(<\/span>private<\/span> http<\/span>:<\/span> HttpClient<\/span>)<\/span> {<\/span> }<\/span>\r\n\r\n- <\/span> getUsers<\/span>():<\/span> Observable<\/span><<\/span>User<\/span>[]<\/span>><\/span> {<\/span>\r\n<\/span>- <\/span>   return<\/span> this<\/span>.<\/span>http<\/span>\r\n<\/span>- <\/span>     .<\/span>get<\/span><<\/span>{<\/span> data<\/span>:<\/span> User<\/span>[]<\/span> }<\/span>><\/span>(<\/span>\"<\/span>https:\/\/reqres.in\/api\/users<\/span>\"<\/span>)<\/span>\r\n<\/span>- <\/span>     .<\/span>pipe<\/span>(<\/span>\r\n<\/span>- <\/span>       map<\/span>(<\/span>resp<\/span> =><\/span> resp<\/span>.<\/span>data<\/span>)<\/span>\r\n<\/span>- <\/span>     );<\/span>\r\n<\/span>- <\/span> }<\/span>\r\n<\/span>+ <\/span> getUsers<\/span>():<\/span> void<\/span> {<\/span>\r\n<\/span>+ <\/span>   this<\/span>.<\/span>http<\/span>\r\n<\/span>+ <\/span>     .<\/span>get<\/span><<\/span>{<\/span> data<\/span>:<\/span> User<\/span>[]<\/span> }<\/span>><\/span>(<\/span>\"<\/span>https:\/\/reqres.in\/api\/users<\/span>\"<\/span>)<\/span>\r\n<\/span>+ <\/span>     .<\/span>pipe<\/span>(<\/span>map<\/span>(<\/span>resp<\/span> =><\/span> resp<\/span>.<\/span>data<\/span>))<\/span>\r\n<\/span>+ <\/span>     .<\/span>subscribe<\/span>(<\/span>users<\/span> =><\/span> this<\/span>.<\/span>_usersSubject<\/span>.<\/span>next<\/span>(<\/span>users<\/span>));<\/span>\r\n<\/span>+ <\/span> }<\/span>\r\n<\/span>}<\/span>\r\n<\/code><\/pre>\n
          \u7136\u540e\uff0c\u4e0d\u4f1a\u8fd4\u56de null\u3002<\/p>\n
          \n
          No\u51e6\u7406_obj_latestValue6createSubscription<\/code>\u3067?\u306e\u8cfc\u8aad\u3092\u958b\u59cb?null
          \n_updateLatestValue()<\/code>\u304c\u547c\u3073\u51fa\u3055\u308c\u308b?null
          \nthis._latestValue<\/code>\u3092\u4e0a\u66f8\u304d?[]<\/code>
          \nmarkForCheck()<\/code>\u304c\u547c\u3070\u308c\u308b?[]<\/code>7return this._latestValue<\/code>?[]<\/code><\/div>\n<\/div>\n
          \u53ea\u8981\u8c03\u7528markForCheck()\uff0c\u53ef\u80fd\u4f1a\u53d1\u751f\u4e00\u4e9b\u9519\u8bef\uff0c\u56e0\u4e3a\u6211\u4e0d\u6e05\u695a\u5b83\u4f1a\u53d1\u751f\u4ec0\u4e48\u3002\u4f46\u662f\uff0c\u5c31\u6700\u65b0\u7684AsyncPipe\u800c\u8a00\uff0c\u5982\u679c\u5728\u8ba2\u9605\u65f6\u540c\u65f6\u6d41\u52a8\u503c\u7684\u662fBehaviorSubject\u7b49\u7b49\u60c5\u51b5\uff0c\u4f3c\u4e4e\u4e0d\u4f1a\u8fd4\u56denull\u3002<\/p>\n
          \u5982\u679c\u6709\u4efb\u4f55\u9519\u8bef\uff0c\u8bf7\u60a8\u6307\u51fa\uff0c\u6211\u5c06\u4e0d\u80dc\u611f\u6fc0?\u200d\u2642\ufe0f\u3002<\/p>\n
          \u660e\u5929\u662fHKT100RTKN\u5148\u751f\u7684\u65e5\u5b50\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"
          \u8fd9\u7bc7\u6587\u7ae0\u662f2022\u5e74Angular\u5723\u8bde\u65e5\u5386\u4e0a\u7b2c20\u5929\u7684\u6587\u7ae0\u3002 \u8fd9\u662f\u5173\u4e8e\u5b66\u4e60AsyncPipe\u7684\u8bb0\u5f55\u3002 \u5f02\u6b65\u7ba1\u9053 […]<\/p>\n","protected":false},"author":4,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-39602","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"\n\u5b66\u4e60Angular\u7684AsyncPipe - Blog - Silicon Cloud<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.silicloud.com\/zh\/blog\/\u5b66\u4e60angular\u7684asyncpipe\/\" \/>\n<meta property=\"og:locale\" content=\"zh_CN\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"\u5b66\u4e60Angular\u7684AsyncPipe\" \/>\n<meta property=\"og:description\" content=\"\u8fd9\u7bc7\u6587\u7ae0\u662f2022\u5e74Angular\u5723\u8bde\u65e5\u5386\u4e0a\u7b2c20\u5929\u7684\u6587\u7ae0\u3002 \u8fd9\u662f\u5173\u4e8e\u5b66\u4e60AsyncPipe\u7684\u8bb0\u5f55\u3002 \u5f02\u6b65\u7ba1\u9053 […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.silicloud.com\/zh\/blog\/\u5b66\u4e60angular\u7684asyncpipe\/\" \/>\n<meta property=\"og:site_name\" content=\"Blog - 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