是什么触发了CombineLatest? [英] what triggered combineLatest?

问题描述

我有一些可观察的东西.而且我需要知道哪个触发了订阅.

I have a few observables. And I need to know which one triggered the subscribe.

Observable.combineLatest(
      this.tournamentsService.getUpcoming(),
      this.favoriteService.getFavoriteTournaments(),
      this.teamsService.getTeamRanking(),
(tournament, favorite, team) => {
//what triggered combinelatest to run?
}).subscribe()

推荐答案

简短的答案是:您不知道. 您可以实施一些解决方法，但这确实很丑陋，我建议您重新考虑用例，以了解为什么需要这样做以及是否可以更改体系结构. 另外请记住，函数的第一个执行将在所有三个可观察对象都发出至少一个值之后进行.

Short answer is: You don't know. You could implement some workaround, however this is really ugly and I would recommend rethinking the usecase why you need this and maybe if you can change the architecture. Also keep in mind, that the first execution of your function will be after all three observables have emitted at least 1 value.

无论如何-可能的解决方法是:

Anyway - a possible workaround could be:

let trigger = "";
Observable.combineLatest(
      this.tournamentsService.getUpcoming().do(() => trigger = "tournament"),
      this.favoriteService.getFavoriteTournaments().do(() => trigger = "favTournament"),
      this.teamsService.getTeamRanking().do(() => trigger = "teamRanking"),
(tournament, favorite, team) => {
   console.log(`triggered by ${trigger}`);
}).subscribe();

如果要基于哪个可观察的触发器执行特定的操作，则应利用每个可观察的触发器并将其用作单独的触发器，然后切换到组合触发器，这可能会花费更多的代码，但是更加简洁，并且您将不会遇到一个丑陋的if/else，切换/遇到一些麻烦的变通办法- plus -您甚至有机会使用async -pipe而不是手动订阅一切，并更新局部变量(无论如何都是不正确的做法):

If you want to execute a specific operation based on which observable triggered, you should make use of each observable and utilize them as individual triggers, that switch to a combined trigger, it might be slightly more code but it is much cleaner and you will not end up in an ugly if/else, switch/case-mess with some hacky workarounds - plus you will have even have the oportunity to use the async-pipe instead of manually subscribing to everything and updating local variables (which is a bad practice anyways):

这是一些看起来像这样的示例代码:

Here is some example code of how this could look like:

let upcoming$ = this.tournamentsService.getUpcoming();
let favorite$ = this.favoriteService.getFavoriteTournaments();
let rankings$ = this.teamsService.getTeamRanking();

let allData$ = Observable.combineLatest(
    upcoming$, favorite$, rankings$,
    (tournament, favorite, team) => {
        return {tournament, favorite, team};
    }
);

// initial call -> this SHOULD be redundant,
// but since I don't know your code in detail
// i've put this in - if you can remove it or not
// depends on the order your data coming in
allData$
    .take(1)
    .do(({tournament, favorite, team}) => {
        this.displayMatches(...);
        this.sortByFavorites(...);
        this.fillWithRanking(...);
    })
    .subscribe();

// individual update triggers
upcoming$
    .switchMapTo(allData$.take(1))
    .do(({tournament, favorite, team}) => this.displayMatches(...))
    .subscribe();

favorite$
    .switchMapTo(allData$.take(1))
    .do(({tournament, favorite, team}) => this.sortByFavorites(...))
    .subscribe();

rankings$
    .switchMapTo(allData$.take(1))
    .do(({tournament, favorite, team}) => this.fillWithRanking(...))
    .subscribe();

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