一次只能订阅多个FormControl

问题描述

我现在已经根据某种逻辑从大型FormGroup中滤除了几个FormControl，我想知道如何合并/组合那些选定的FormControl，并且只有一个订阅..

I have filtered out few FormControl(s) from a large FormGroup based on some logic now - I'd like to know how can I merge / combine those selected FormControls and have only one subscribe..

我查看了RxJS文档和大理石图，但对它的理解不正确.理解所有这些并知道要为我的案例使用哪一个是非常令人困惑的:

I looked into RxJS docs and marble diagrams but didn't understand it properly. It's very confusing to understand all of these and know which one to use for my case:

- forkJoin
- combineLatest
- merge
- join
- zip

以下是有关该问题的详细信息:

Here's more detailed info about the question:

让我们说2个FormControls(即controlA，controlB).每当任何FormControl值更改时，我都想执行一些handlerFunction.*每当任何控件值更改时，都需要执行一次我的handlerFunction(在我的情况下，一次更改任何一个控件)

Let's say 2 FormControls (i.e., controlA, controlB). I want to execute my some handlerFunction whenever any of the FormControl value changes.* It needs to execute my handlerFunction once whenever any control valueChanges (In my case any one control will be changed at one time)

谢谢.

推荐答案

对您而言，最好的选择是combineLatest，它在所有源Observable都发出至少一个值之后，然后在任何源Observable的每次发出之后发出:

The best option for you is combineLatest that emits after all source Observables emitted at least one value and then on every emission from any source Observable:

Observable.combineLatest(controlA.valueChanges, controlB.valueChanges)
  .subscribe(...);

最终，您可以将每个源与startWith(null)链接在一起，以确保每个源都将立即发出一个项目并过滤订户中想要的内容.

Eventually you can chain each source with startWith(null) to guarantee that every source will emit one item immediately and filter what you want in the subscriber.

Observable.combineLatest(
    controlA.valueChanges.startWith(null),
    controlB.valueChanges.startWith(null)
  )
  .subscribe(([val1, val2]) => ...);

顺便说一句，关于其他运算符:

Btw, about the other operators:

• zip-仅在所有来源发出相同数量的物品时发出
• forkJoin-当所有来源发出至少一项并完成时发出(valueChanges从未发生)
• merge-只是合并Observables，但您不知道哪一个发出了什么值
• join-我认为这不是RxJS 5的一部分

• zip - emits only when all sources emitted the same number of items
• forkJoin - emits when all sources emitted at least one item and completed (never happens with valueChanges)
• merge - just merges Observables but you can't know which one emitted what value
• join - I don't think that's part RxJS 5

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