C# Rx Observable.Never<> 表现得像 Observable.Empty<>？

Question

I'm new to Rx and have this code snippet for a try.

Observable.Never<string>().Subscribe(Console.Write);
Observable.Empty<string>().Subscribe(Console.Write);

I expected that Never<string>() will behave like Console.ReadKey which will not end, but as I run these 2 lines, they end immediately, so [Never] behaves like [Empty] to me.

What is the correct understanding of [Never] and is there a good sample usage for it?

Answer 1

Both the Observable.Never() and Observable.Empty() observable will not emit any values. However, the observable built with Observable.Never() will not complete and instead stays "open/active". It might be a difference at the location where you consume these observable if the observable completes ( Empty() ) or not ( Never() ), but this depends on your actual use-case.

Having observables which doesn't emit any values might sound useless, but maybe you are at a location where you have to provide an observable (instead of using null ). So you can write something like this:

public override IObservable<string> NameChanged => Observable.Never<string>();

Answer 2

So I don't have a ton of experience with Rx, but I believe all Subscribe is doing is registering what to do when the observable emits. If your observable never emits (ie Empty or Never ) then the method is never called. The application is not waiting for the subscription itself to end. If you wanted to wait forever you would use something like

Observable.Never<string>().Wait();

This ties back into the reason you should not use async operation in Subscribe . Take the following code

static void Main(string[] args)
{
  Observable.Range(1, 5).Subscribe(async x => await DoTheThing(x));
  Console.WriteLine("done");
}

static async Task DoTheThing(int x)
{
  await Task.Delay(TimeSpan.FromSeconds(x));
  Console.WriteLine(x);
}

When run the application will immediately write "done" and exit after pushing the values into the observable because it is unaware of the subscriber in the context of whether it has completed its handling or not. Hopefully I made that clear, and if someone with more Rx knowledge wants to step in to help if needed that'd be good.

Answer 3

此链接给你空的，从来没有，也扔的区别： http://reactivex.io/documentation/operators/empty-never-throw.html这是从来没有的一个用法： HTTPS：//rxjs-dev.firebaseapp .com/api/index/const/从不