Fixed issue where RowDetailsTemplate was getting the wrong DataContext

[GundlackFlorian]

Hello,

in this issue i noticed that the RowDetailsTemplate was getting the wrong DataContext when the first measurement pass was done which could cause a InvalidCastException or a StackOverflow (if a ContentControl is used).

What is the current behavior?

Avalonia/src/Avalonia.Controls.DataGrid/DataGridRows.cs

Lines 2967 to 2977 in 1940446

	if(VisibleSlotCount > 0)
	dataItem = DataConnection.GetDataItem(0);
	var detailsContent = RowDetailsTemplate.Build(dataItem);
	if (detailsContent != null)
	{
	_rowsPresenter.Children.Add(detailsContent);
	if (dataItem != null)
	{
	detailsContent.DataContext = dataItem;
	}
	detailsContent.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));

Right now the detailsContent.DataContext is only changed if the dataItem is not null.
So when no list or an empty one is provided detailsContent.DataContext is not changed and it's still on the value provided by _rowsPresenter.Children.Add(detailsContent); (which is the DataContext of the DataGrid).

What is the updated/expected behavior with this PR?

I removed the null check of the dataItem so:

• If the dataItem is set, detailsContent.DataContext will the item.
• If there no dataItem, the detailsContent.DataContext is set to null.

After this change the issues mentioned above are not happening anymore.
I tested setting the ItemsSource:

• Empty list -> works
• List with items -> works
• null -> works

Also no problem with RowDetailsVisibilityMode=Collapsed/Visible/VisibleWhenSelected

More details in the issue.

Fixed issues

Fixes #12106

[GundlackFlorian]

@dotnet-policy-service agree

[timunie]

Thx 🙏

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0037675-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[GundlackFlorian]

You can test this PR using the following package version. 11.0.999-cibuild0037675-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

After testing with the build (i'm using the test project of the issue), the StackOverflow is fixed, but not the InvalidCastException.
I moved the detailsContent.DataContext = dataItem before the _rowsPresenter.Children.Add(detailsContent).

Waiting for the next PRBUILD to test again.

[avaloniaui-team]

You can test this PR using the following package version. 11.0.999-cibuild0037679-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[GundlackFlorian]

11.0.999-cibuild0037679-beta works !