CollectionView with GridItemsLayout: Issues when changing Span

[Forestbrook]

Description

I have a CollectionView with a GridItemsLayout. Depending on the available size I want to show more (landscape view) or less (portrait view) items on a row.

In the SizeChanged event I compute and set the right Span.

• On iOS: crash with NullReferenceException: CollectionView is null in GridViewLayout.HandlePropertyChanged().
• On Windows: Number of items on the row is NOT changed.
• On Android: When I add a short delay before changing Span it seems to work correct.

Steps to Reproduce

See example project MauiGridItemsLayoutChangeSpanIssue

In the AppShell Flyout you can select two views:

• CollectionView with workaround and
• CollectionView with bug

Rotate the phone/tablet to see the number of items on a row change.

Version with bug

6.0.400 (current)

Last version that worked well

Unknown/Other

Affected platforms

iOS, Windows

Affected platform versions

iOS 15.5, Windows 10.0.19044

Did you find any workaround?

For iOS I found a workaround by adding a check for CollectionView==null in GridViewLayout.HandlePropertyChanged(). See GridViewLayoutExt in the example project. This works, because HandlePropertyChanged() for the Span property is called again when CollectionView is not null anymore, which is kinda weird.

For Windows I did not look for a workaround yet.

Relevant log output

No response

[GalaxiaGuy]

This currently happens to me in Forms too (oddly enough I haven't reported a bug for it, but the comment I left in my code makes me think it's the same issue):

// Trying to set the Span on the existing gridLayout sometimes throws a NullReferenceException from deep within Forms

A workaround that worked for me is to create a new GridItemsLayout with the new Span value.

[kristinx0211]

verified repro on IOS15.4 and windows with above project.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[BenderNK]

Provided work-around does not work in Windows.

A workaround that worked for me is to create a new GridItemsLayout with the new Span value.

Specifically this:

var newSpanValue = 5
MyCollectionView.ItemsLayout = new GridItemsLayout(span: newSpanValue, ItemsLayoutOrientation.Vertical);

Neither this:

if (MyCollectionView.ItemsLayout is GridItemsLayout gridItemsLayout)
{
    var newSpanValue = 5
    gridItemsLayout.Span = newSpanValue ;
}

Nothing ever happens. Original span value that was provided in the XAML is only being respected. Also this open issue appears to be related.

[hartez]

See also: #10144.