[windows] fix memory leak when CollectionView.ItemsSource changes

[jonathanpeppers]

Fixes #13393
Context: https://github.com/ivan-todorov-progress/maui-collection-view-memory-leak-bug

Debugging the above sample, I found that ItemsView._logicalChildren grew indefinitely in size if you replace a CollectionView's ItemsSource over and over.

I could fix this by creating a new internal ItemsView.ClearLogicalChildren() method and call it from the Windows ItemsViewHandler.

I could reproduce this issue in a Device Test running on Windows.

It appears the problem does not occur on Android or iOS due to the recycling behavior of the underlying platforms.

For example, Android calls OnViewRecycled() which calls RemoveLogicalChild(view):

maui/src/Controls/src/Core/Handlers/Items/Android/Adapters/ItemsViewAdapter.cs

Lines 52 to 57 in 53f6e39

	public override void OnViewRecycled(Object holder)
	{
	if (holder is TemplatedItemViewHolder templatedItemViewHolder)
	{
	templatedItemViewHolder.Recycle(ItemsView);
	}

maui/src/Controls/src/Core/Handlers/Items/Android/TemplatedItemViewHolder.cs

Lines 37 to 45 in 53f6e39

	public void Recycle(ItemsView itemsView)
	{
	if (View == null)
	{
	return;
	}
	itemsView.RemoveLogicalChild(View);
	}

On Windows, we merely have a ItemContentControl and there is no callback for when things are recycled. We do get a callback for when the FormsDataContext value changes, so an option is to clear the list in this case.

After this change, my test passes -- but it was already passing on iOS and Android.

[jonathanpeppers]

It appears there is no issue on Android, iOS, or Catalyst:

Going to investigate why this is only needed on Windows.

[jonathanpeppers]

Ok Android works, because there is a callback for "recycling":

maui/src/Controls/src/Core/Handlers/Items/Android/Adapters/ItemsViewAdapter.cs

Lines 52 to 57 in 53f6e39

	public override void OnViewRecycled(Object holder)
	{
	if (holder is TemplatedItemViewHolder templatedItemViewHolder)
	{
	templatedItemViewHolder.Recycle(ItemsView);
	}

maui/src/Controls/src/Core/Handlers/Items/Android/TemplatedItemViewHolder.cs

Lines 37 to 45 in 53f6e39

	public void Recycle(ItemsView itemsView)
	{
	if (View == null)
	{
	return;
	}
	itemsView.RemoveLogicalChild(View);
	}

I'll continue looking tomorrow, it appears that Windows uses this ItemContentControl, and there is no callback when things are "recycled":

maui/src/Controls/src/Core/Platform/Windows/CollectionView/ItemContentControl.cs

Lines 36 to 37 in 53f6e39

	var itemContentControl = (ItemContentControl)d;
	itemContentControl.Realize();

[github-actions]

Thank you for your pull request. We are auto-formating your source code to follow our code guidelines.

[JanZeman]

Thank you @jonathanpeppers for this fix. I am afraid I do not know the merging strategy but to my understanding the main branch will become available as 8-preview. Is there any chance these important memory-related fixes go backported into net-7? Or what is my chance to test it within my projects in the foreseeable future?

[jonathanpeppers]

I don't know how the backporting works for MAUI (I am on the Android team). This one seems like very minimal risk; I put the label so they can take a look.

[JanZeman]

Thank you!

[PureWeen]

/backport to net7.0

[github-actions]

Started backporting to net7.0: https://github.com/dotnet/maui/actions/runs/4315685016