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

问题描述

我有一些可观察的.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

简短的回答是:你不知道.您可以实施一些解决方法，但这真的很难看，我建议重新考虑用例为什么需要它，也许您可​​以更改架构.还要记住，您的函数的第一次执行将是在所有三个 observable 都发出至少 1 个值之后.

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();

如果你想根据触发的 observable 执行特定的操作，你应该利用每个 observable 并将它们用作单独的触发器，切换到组合触发器，它可能会稍微多一些代码但它更清晰和你不会以丑陋的 if/else、switch/case-mess 和一些 hacky 解决方法结束 - plus 你甚至有机会使用 async-pipe而不是手动订阅所有内容并更新局部变量(无论如何这是一个不好的做法):

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):

以下是一些示例代码，说明其外观:

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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