[maccatalyst] UICollectionViewSource is missing methods

[jeromelaban]

Description

The following methods are present in xamarinios10 and net6.0-ios but are not present in net6.0-maccatalyst:

• UICollectionViewSource.Scolled
• UICollectionViewSource.DraggingStarted
• UICollectionViewSource.DraggingEnded
• UICollectionViewSource.DidZoom
• UICollectionViewSource.WillEndDragging
• UICollectionViewSource.DecelerationEnded
• UICollectionViewSource.ScrollAnimationEmded

Environment

6.0.100-preview.3.21202.5

[spouliot]

Keep in mind that MacCatalyst support, even for the current (soon legacy) SDK is a preview and incomplete. YMMV.

The API surface for iOS and Catalyst are not totally identical. We're trying to solve this by shipping a Xamarin.iOS.dll along with Xamarin.MacCatalyst.dll.

This special Xamarin.iOS.dll contains:

• type forwarders to Xamarin.MacCatalyst.dll when an API is available on Catalyst;
• empty stubs that will throw a PlatformNotSupportedException for other, non available, API

The above trick was not generating a perfect/total coverage for P3 (it was incomplete at P3 release time).
This should be accurate for P4 (or it will be a bug in our tooling).

Note that we're still missing some API annotations for Catalyst so it's still possible something will throw (while it should be supported) or crash (because it should be throwing). However it should build fine when Xamarin.iOS.dll is used.

Now if you're referencing Xamarin.MacCatalyst.dll directly then some missing (or incorrect) annotations might be excluding some API. We have tools to report those errors - but there's quite a backlog to process until completion. If you're blocked by something then feel free to open bugs and we'll prioritize those API (over others) for the next release(s).

Q: What assembly are you referencing ? (any build logs?)

[jeromelaban]

Thanks for the very detailed answer! No worries about the preview state, that's to be expected for sure.

I'm not referencing anything specific, aside from net6.0-maccatalyst, and looking at the IL disassembly of UICollectionViewSource in Xamarin.MacCatalyst.dll I see that those members are also effectively missing.

The source is basically doing something like this:

public partial class MySource : UICollectionViewSource
{
	public override void Scrolled(UIScrollView scrollView)
	{
		InvokeOnScroll();
	}
}

[spouliot]

This seems to be because XAMCORE_3_0 is defined, like tvOS and watchOS. This does remove a few mistakes (on both our and Apple sides) but reduce compatibility in those corner cases.

src/Makefile:MACCATALYST_GENERATED_DEFINES= -d:__MACCATALYST__ -d:XAMCORE_3_0 -d:IOS

[spouliot]

You can see the API in the (just merged) API diff
https://gist.github.com/vs-mobiletools-engineering-service2/3329d5705cffab4bb74f418414111b77