[Bug]: SortAndBind with IObservable<IComparer> not working as expected

[DevEngineReq]

Describe the bug 🐞

If we use SortAndBind with an IObservable we have to use ObserveOn(RxApp.MainThreadScheduler) for the compare observable, otherwise the application will freeze. For the deprecated .Sort() method it was not required.

This behavour can cause wired problems if you switches from .Sort to SortAndBind with just coping the compare observable.

Step to reproduce

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Reproduction repository

https://github.com/reactivemarbles/DynamicData

Expected behavior

See Descriptions

Screenshots 🖼️

No response

IDE

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Operating system

No response

Version

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Device

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DynamicData Version

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Additional information ℹ️

No response

[JakenVeina]

I can agree this looks unintuitive, but it's very much to be expected, and is in fact a behavior you can get with the separate .Sort() and Bind() operator.

Using the .SortAndBind() operator as in your example is the equivalent of doing the following:

this.cacheObservable = this.userCache.Connect()
    .ObserveOn(RxApp.MainThreadScheduler)
    .Sort(sorterObservable)
    .Bind(this.users)
    .Subscribe();

The issue is that there are 2 separate streams feeding input into the .Sort() operation, the .Connect() stream, and sorterObservable. When .Sort() and .Bind() are separate, it's trivial to insert the proper .ObserveOn() after the .Sort(), when the two separate streams have been merged into just one. But without that, you need to apply .ObserveOn() to both input streams, separately.

It sounds like we should add an optional scheduler parameter to .SortAndBind() to support this scenario, and to help clarify for folks migrating to it that a scheduler may be necessary.

[DevEngineReq]

Like this

It would be nice if the stream would go ahead with the entered scheduler after SortAndBind(....)

[JakenVeina]

Yes, you'd end up with the downstream being driven by that scheduler.

[DevEngineReq]

Any news on this issue?

Will there be an optional scheduler parameter to .SortAndBind() like described above?

[JakenVeina]

In fact, this has just been added and released. You can now supply an IScheduler to .SortAndBind() via the options parameter.

I'll leave the issue open for the moment, until you can confirm whether this resolves the issue.

[DevEngineReq]

Works as expected. Thank you

[github-actions]

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