AdvancedCollectionView is not NULL annotated correctly

[Balkoth]

Describe the bug

While this

AdvancedCollectionView acv = new AdvancedCollectionView();
acv.Add(null);

is working as the underlying source is an IList which supports this behaviour, all the methods in AdvanceCollectionView are missing the null annotations. Nevertheless this code, after updating to v8 now displays a warning: CS8625 Cannot convert null literal to non-nullable reference type.

Steps to reproduce

object? item = null;
AdvancedCollectionView acv = new AdvancedCollectionView();
acv.Add(item);      // <- warning here
acv.Contains(item); // <- warning here

Expected behavior

Expected behaviour is as it was before v8, no warnings.

Screenshots

No response

Code Platform

• [ ] UWP
• [X] WinAppSDK / WinUI 3
• [ ] Web Assembly (WASM)
• [ ] Android
• [ ] iOS
• [ ] MacOS
• [ ] Linux / GTK

Windows Build Number

• [ ] Windows 10 1809 (Build 17763)
• [ ] Windows 10 1903 (Build 18362)
• [ ] Windows 10 1909 (Build 18363)
• [ ] Windows 10 2004 (Build 19041)
• [ ] Windows 10 20H2 (Build 19042)
• [ ] Windows 10 21H1 (Build 19043)
• [ ] Windows 10 21H2 (Build 19044)
• [X] Windows 10 22H2 (Build 19045)
• [ ] Windows 11 21H2 (Build 22000)
• [ ] Other (specify)

Other Windows Build number

No response

App minimum and target SDK version

• [ ] Windows 10, version 1809 (Build 17763)
• [ ] Windows 10, version 1903 (Build 18362)
• [ ] Windows 10, version 1909 (Build 18363)
• [ ] Windows 10, version 2004 (Build 19041)
• [X] Windows 10, version 2104 (Build 20348)
• [ ] Windows 11, version 22H2 (Build 22000)
• [ ] Other (specify)

Other SDK version

No response

Visual Studio Version

2022

Visual Studio Build Number

No response

Device form factor

Desktop

Additional context

No response

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[michael-hawker]

Thanks for the report @Balkoth, so the fix is to just add the ? to the types on the parameters to the methods in the AdvancedCollectionView?

Is there a reason to be adding null to this type of collection though? Shouldn't we want warnings against that?

Otherwise, I'm wondering if this would already be considered a breaking change though... 🤔

[Balkoth]

I guess that is open for discussion, but it was allowed previuosly and i would consider this a change now, when it warns, when it is valid to have null values in there.

So what is the general opinion on this?

[Balkoth]

Just some food for thought:

List<object?> objects = new List<object?>();
objects.Add(new object());
objects.Add(null);
AdvancedCollectionView acv = new AdvancedCollectionView(objects);

This code is also perfectly valid and no warnings are given. My opinion is that AdvancedCollectionView has to live with the nullabilty of the objects the collection can contain. Otherwise we create a false sense of security for the developer, when there is none.