[BUG] ReactiveCommand Execute() runs before subscribe

[jalbertSyncroTech]

Describe the bug

According to this documentation comment, ReactiveCommand Execute() should not run the associated command logic until the returned observable is subscribed.

"Invoking this method will return a cold (lazy) observable that, when subscribed, will execute the logic encapsulated by the command. It is worth restating that the returned observable is lazy. Nothing will happen if you call Execute and neglect to subscribe (directly or indirectly) to the returned observable."

ReactiveUI/src/ReactiveUI/ReactiveCommand/ReactiveCommandBase.cs

Line 153 in eaa4abf

/// Invoking this method will return a cold (lazy) observable that, when subscribed, will execute the logic

However, this change replaced the call to
Observable.StartAsync(execute)
with
() => execute().ToObservable(),
which incorrectly executes the command logic immediately.

93823ff

Steps To Reproduce

• Call ReactiveCommand.Execute()

Expected behavior

• The logic in the command should not be executed (until .Subscribe() or await is used)

[jalbertSyncroTech]

Looking over the code, I think this issue may have existed before the referenced commit. The previous code is using StartAsync(), but I think it would need to use FromAsync() to get the semantics described in the documentation.

For reference, via StackOverflow "Observable.FromAsync vs Task.ToObservable"
https://stackoverflow.com/a/39053198

"Observable.FromAsync accepts a TaskFactory in the form of Func or Func<Task>, in this case, the task is only created and executed, when the observable is subscribed to."

Stack Overflow

Observable.FromAsync vs Task.ToObservable

Does anyone have a steer on when to use one of these methods over the other. They seem to do the same thing in that they convert from TPL Task to an Observable.

Observable.FromAsync appear to sup...

[glennawatson]

Thanks for the research will look into it most likely today.

[github-actions]

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