CollectionView with EmptyView and EmptyViewTemplate for Data template selector throws an exception

[Vignesh-SF3580]

Root Cause

The exception occurred because the RealizeView method in the ItemsViewController file was attempting to create and render a view when both EmptyView and EmptyViewTemplate were defined in the CollectionView, with a DataTemplateSelector for the EmptyViewTemplate. The original code did not account for the scenario where the viewTemplate was a DataTemplateSelector. In this case, the RealizeView method expected a DataTemplate to be directly provided, leading to a null reference issue when trying to use the viewTemplate. This caused an exception when it encountered a DataTemplateSelector, which should dynamically choose the correct template based on the input data.

Description of Change

The fix introduced an additional condition to handle cases where the viewTemplate is a DataTemplateSelector. This ensures that when the view is null and the viewTemplate is either null or a DataTemplateSelector, the logic correctly bypasses attempting to realize a non-existent view. This fix code prevents the exception by ensuring that the method can handle DataTemplateSelector cases, avoiding invalid template realization, and allowing the CollectionView to display the appropriate empty view template without errors.

Tested the behaviour in the following platforms

• Android
• Windows
• iOS
• Mac

Issues Fixed

Fixes #25224

Screenshots

iOS:

Before Issue Fix	After Issue Fix
	)

Mac:

Before Issue Fix	After Issue Fix

[jsuarezruiz]

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[jsuarezruiz]

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[jsuarezruiz]

/rebase

[jsuarezruiz]

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[PureWeen]

/rebase

[PureWeen]

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[jsuarezruiz]

The tests are failing on iOS and Catalyst

[jsuarezruiz]

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[praveenkumarkarunanithi]

/rebase

[jsuarezruiz]

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[jsuarezruiz]

From the PR description:

"The exception occurred because the RealizeView method in the ItemsViewController file was attempting to create and render a view when both EmptyView and EmptyViewTemplate were defined in the CollectionView, with a DataTemplateSelector for the EmptyViewTemplate. The original code did not account for the scenario where the viewTemplate was a DataTemplateSelector."

In the case of using a DataTemplateSelector, here

maui/src/Controls/src/Core/Handlers/Items/iOS/TemplateHelpers.cs

Line 34 in bd61427

viewTemplate = viewTemplate.SelectDataTemplate(view, itemsView);

should select the correct template, and then get the content to create the handler and the PlatformView.

Is the SelectTemplate method returning null?

[praveenkumarkarunanithi]

@jsuarezruiz ,
In this case, the SelectTemplate method itself isn't returning null. Instead, the exception occurs immediately afterward, when the selected viewTemplate is used in CreateContent. This happens because, on the initial render, there's no template available to select, resulting in viewTemplate being null. This leads to an exception when CreateContent is called with an empty or unassigned DataTemplateSelector.

Let me know if further clarification is needed!

[PureWeen]

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Changes Addressed