`LayoutSlot` is invalid

[dr1rrb]

Current behavior

The LayoutInformation.GetLayoutSlot does not give same result as UWP

Expected behavior

🙃

How to reproduce it (as minimally and precisely as possible)

In a blank app

<Border x:Name="Outer" Loaded="DumpData" BorderThickness="20" HorizontalAlignment="Left" VerticalAlignment="Top" Width="100" Height="100" BorderBrush="Red" Background="Blue">
    <Border x:Name="Inner" Loaded="DumpData" HorizontalAlignment="Left" VerticalAlignment="Top" Width="10" Height="10" Background="DeepPink" />
</Border>

private void DumpData(object sender, object o)
{
    var elt = (FrameworkElement)sender;
    Console.WriteLine($"{elt.Name} layout slot:{F(LayoutInformation.GetLayoutSlot(elt))} origin: {elt.TransformToVisual(this).TransformPoint(new Point())}");

    string F(Rect rect) => $"{rect.Width:F2}x{rect.Height:F2}@{rect.X:F2},{rect.Y:F2}";
}

UWP (expected)

Inner layout slot:60.00x60.00@20.00,20.00 origin: 20,20 Outer layout slot:1920.00x1048.00@0.00,0.00 origin: 0,0

Android

Inner layout slot:10.00x10.00@0.00,0.00 origin: [20, 20] Outer layout slot:100.00x100.00@0.00,0.00 origin: [0, 0]

Workaround

None

Works on UWP/WinUI

No response

Environment

No response

NuGet package version(s)

3.10.0-dev.632

Affected platforms

Android

IDE

No response

IDE version

No response

Relevant plugins

none

Anything else we need to know?

Not validated yet on iOS

Ok on Skia and WASM

[ramezgerges]

I just tested this on skia. Also broken. The problem is that Loaded is fired before Arrange, so LayoutSlot will still be the default value. A simple workaround is to queue the callback.

        private void DumpData(object sender, object o)
        {
            DispatcherQueue.TryEnqueue(new Microsoft.UI.Dispatching.DispatcherQueueHandler(new Action(() =>
            {
                var elt = (FrameworkElement)sender;
                global::System.Diagnostics.Debug.WriteLine($"{elt.Name} layout slot:{F(Microsoft.UI.Xaml.Controls.Primitives.LayoutInformation.GetLayoutSlot(elt))} origin: {elt.TransformToVisual(this).TransformPoint(new Point())}");

                string F(Rect rect) => $"{rect.Width:F2}x{rect.Height:F2}@{rect.X:F2},{rect.Y:F2}";
            })));
        }

This will probably be fixed by @Youssef1313 lifecycle work.

[Youssef1313]

This may have been fixed on Skia.