Transition doesn't work when I set RenderTransform using code

[qingyu-sama]

Describe the bug

When I set the RenderTransform using Style , the Transition works fine

<Style Selector="Button">
    <Setter Property="Height" Value="{Binding Size}" />
    <Setter Property="Width" Value="{Binding Size}" />
    <Setter Property="Background" Value="Transparent" />
    <Setter Property="Foreground" Value="Transparent" />
    <Setter Property="BorderBrush" Value="Transparent" />
    <Setter Property="BorderThickness" Value="0" />
    <Setter Property="VerticalAlignment" Value="Center" />
    <Setter Property="HorizontalAlignment" Value="Center" />
    <Setter Property="Opacity" Value="0" />
    <Setter Property="Transitions">
        <Transitions>
            <DoubleTransition Property="Opacity"
                              Duration="0.2"
                              Easing="QuarticEaseOut" />
            <TransformOperationsTransition Property="RenderTransform"
                                           Duration="0.2"
                                           Easing="QuarticEaseOut" />
        </Transitions>
    </Setter>
</Style>

<Button Classes.open="{Binding IsOpen}">
    <Button.Styles>
        <Style Selector="Button.open">
            <Setter Property="RenderTransform" Value="translateX(78px)" />
        </Style>
    </Button.Styles>
    <Image Source="..." />
</Button>

But when I set the RenderTransform using code instead, the Transition works in a weird way, including the DoubleTransition of Opacity

for (var i = 0; i < Container.Children.Count; i++) {
    var child = Container.Children[i];

    if (data.IsOpen)
        child.RenderTransform = new TranslateTransform((i + 1) * FloatingBarViewModel.Size, 0);
    else
        child.RenderTransform = new TranslateTransform();
}

To Reproduce

As mentioned above

Expected behavior

No response

Avalonia version

11.2.0-rc1

OS

Windows, Android

Additional context

No response

[timunie]

Try child.SetValue or SetCurrentValue

[maxkatz6]

From what I remember, XAML transform value is actually emit as new TransformOperations.Builder(1).AppendTranslate(78, 0).Build(), which had different transition rules.

[timunie]

This seems to work:

private void Button_OnClick(object? sender, RoutedEventArgs e)
{
    if (sender is Button btn)
    {
        var builder = new TransformOperations.Builder(1);
        builder.AppendTranslate(78, 0);
        
        btn.RenderTransform = builder.Build();
    }
}

@maxkatz6 do you think this is by design?