[BUG] When binding received parameter in ContentPage from INavigable ViewModel exception is thrown that cannot access UI control from another thread

[xplatsolutions]

[BUG] When binding received parameter in ContentPage from INavigable ViewModel exception is thrown that cannot access UI control from another thread

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[winterdouglas]

I couldn't reproduce the exact same issue as is described here, it doesn't crash with the version 2.2.1. For the test I used Forms 4.4, RxUI 11. Tried the latest Sextant 2.4.1 as well, doesn't crash either. However, there are a few remarks:

1. On iPhone XR iOS 12.4 the BindValidation fails with an IndexOutOfRangeException. The same doesn't happen if I run the exact same code on iOS 13.
2. The WhenNavigatingTo runs out of the main thread (should it? @RLittlesII), and then the property is set as is, which makes it to not update the UI on iOS. It doesn't crash for me, just the value that doesn't get displayed in the view.
3. If I do force the property to be set on the main thread, everything works well (except that BindValidation above, I had to comment it out to run on iOS 12.4).

[RLittlesII]

@winterdouglas It should execute on the main thread, or whatever thread the View believes is the main thread. Although looking at it now and remembering an issue I had a few weeks ago, this is most likely not happening on the main thread.

Sextant/src/Sextant/Navigation/ParameterViewStackService.cs

Lines 54 to 65 in b4fda78

	navigableViewModel
	.WhenNavigatingTo(parameter)
	.ObserveOn(View.MainThreadScheduler)
	.Subscribe(navigating => Logger.Debug($"Called `WhenNavigatingTo` on '{navigableViewModel.Id}' passing parameter {parameter}"));
	AddToStackAndTick(PageSubject, navigableViewModel, resetStack);
	Logger.Debug($"Added page '{navigableViewModel.Id}' (contract '{contract}') to stack.");
	navigableViewModel
	.WhenNavigatedTo(parameter)
	.ObserveOn(View.MainThreadScheduler)
	.Subscribe(navigated => Logger.Debug($"Called `WhenNavigatedTo` on '{navigableViewModel.Id}' passing parameter {parameter}"));

[gsgou]

i reproduce the same issue on:
Device: iPhone 6S 12.4
Version: Sextant.XamForms 2.10.1