ListBox crashes the built app when a PaintCellBackground handler exists

madru

In the built app (not in debug mode), refilling a ListBox (RemoveAllRows, changing ColumnCount, AddRow) crashes the process when the window has a ListBox1_PaintCellBackground handler, even if the handler only returns False. Removing the handler avoids it.

Unhandled exception. System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')
at System.Collections.Generic.List`1.get_Item(Int32 index)
at Objo.StdLib.Desktop.ListBoxMethods.ListBoxPhantomBackground.UpdateCells()
at Objo.StdLib.Desktop.ListBoxMethods.ListBoxPhantomBackground.OnLayoutUpdated(Object sender, EventArgs e)
at Avalonia.Layout.Layoutable.LayoutManagedLayoutUpdated(Object sender, EventArgs e)
at Avalonia.Layout.LayoutManager.ExecuteLayoutPass()
...

Garry

Thanks for the clear report and stack trace. Yes, this is an Objo bug. A PaintCellBackground handler that returns False should never crash the app. The exception is coming from ListBox’s internal background painting; I suspect it occurs while the columns are being rebuilt, but that still needs confirming in a built app.

I’ve logged it here and will get it fixed: https://feedback.objo.dev/bug/1615

For now, removing the handler avoids the crash if you can do without custom cell backgrounds. If you can share a small project that reproduces it, along with your Studio version and operating system, that would help confirm the built-app behaviour otherwise I'll crack on without one.

Garry

This has been fixed for the next release.