Fixed Header and Footer template is not visible in CollectionView

[NirmalKumarYuvaraj]

Issue Details:

When both the HeaderTemplate and FooterTemplate are declared for a CollectionView, neither template is visible in the view.

Root Cause:

In the StructuredItemsView handler, the UpdateHeader() and UpdateFooter() methods return null for the Header property, resulting in the switch case returning null as well. Additionally, both the Header and MauiContext are found to be null when mapped to the native ListViewBase.Header, causing the header to fail to render properly

Description of Change:

Fixed by recalculating the Header value to account for both the Header and HeaderTemplate. Furthermore, the MauiContext was explicitly passed as a parameter to the ItemTemplateContext during the mapping process. This ensures that the MauiContext is properly associated with ListViewBase.Header, enabling the header to render as expected. Processed same for footer template in UpdateFooter()

Tested the behavior in the following platforms.

• Android
• Windows
• iOS
• Mac

Issue not reproduced in iOS and macOS platforms as it is fixed by this PR #25418

Issues Fixed:

Fixes #22892

Screenshots

Before Issue Fix	After Issue Fix

[PureWeen]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[PureWeen]

If we just left this as var header = ItemsView.Header

And then just deleted the
case null:

would that do the same thing?

We might still want it to fall through to the default case

That way it will set both Header properties on the ListViewBase to null

[rmarinho]

I think this is fine as is but I would change this to be a boolean, HasHeader and change switch statement. for example. ON the null I would also would make sure we clear the ListViewBase.HeaderTemplate just in case

[mattleibow]

Previous comment was wrong :)

Having the switch here is fine, but the default case still having to check the header is a bit redundant? I would think it should just be a case DataTemplate headerTemplate:

And then we would not need the null and default would be the null where we null out both.

[rmarinho]

I think we still need the null if you clear the template and we want to clear on the native side too.

[rmarinho]

Needs some tweaks

[rmarinho]

I think this is fine as is but I would change this to be a boolean, HasHeader and change switch statement. for example. ON the null I would also would make sure we clear the ListViewBase.HeaderTemplate just in case