The source code of scrollviewer feels not up to date

[kyuranger]

What I want to achieve is to display a small scrollbar on the scrollviewer. Just like this:

At the same time, I don't want the scrollbar to be enlarged like this when the mouse moves over it.

So, I tried to find its source code to override this.

And then I found this:
https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.Themes.Fluent/Controls/ScrollViewer.xaml

However, it has no style about mouse over it that I don't know how to override it.

I suspect this is not the latest source code of scrollviewer, or am I doing something wrong?

[DoubleDBE]

I think you have to take a look at ScrollBar instead of ScrollViewer.

[kyuranger]

ScrollBar seems has not any about this also.

[stevemonaco]

You should be looking at ScrollBar.IsExpanded.

Theme:

Avalonia/src/Avalonia.Themes.Fluent/Controls/ScrollBar.xaml

Lines 268 to 284 in 9e6d3cf

	<Style Selector="^[IsExpanded=true]">
	<Style Selector="^ /template/ Grid#Root">
	<Setter Property="Background" Value="{DynamicResource ScrollBarBackgroundPointerOver}" />
	</Style>
	<Style Selector="^ /template/ Rectangle#TrackRect">
	<Setter Property="Fill" Value="{DynamicResource ScrollBarTrackFillPointerOver}" />
	<Setter Property="Stroke" Value="{DynamicResource ScrollBarTrackStrokePointerOver}" />
	<Setter Property="Opacity" Value="1" />
	</Style>
	<Style Selector="^ /template/ Thumb">
	<Setter Property="Background" Value="{DynamicResource ScrollBarThumbBackgroundColor}" />
	<Setter Property="RenderTransform" Value="none" />
	</Style>
	<Style Selector="^ /template/ RepeatButton">
	<Setter Property="Opacity" Value="1" />
	</Style>
	</Style>

Code to follow through several method calls until IsExpanded = IsPointerOver is set:

Avalonia/src/Avalonia.Controls/Primitives/ScrollBar.cs

Lines 293 to 301 in f7bcb5f

	protected override void OnPointerEntered(PointerEventArgs e)
	{
	base.OnPointerEntered(e);
	if (AllowAutoHide)
	{
	ExpandAfterDelay();
	}
	}

Not sure exactly what you want, but you may need to re-theme the ScrollBar.

[kyuranger]

I always thought it was implemented through style, but it turned out to be implemented through code-behind. It seems that if I want to achieve what I want, I have to rewrite the entire scrollbar (IsExpanded is a read-only property), which is quite a huge work.

[stevemonaco]

You can re-theme the ScrollBar, but there's no need for the code side. Just ignore the IsExpanded state in your new ControlTheme.

[kyuranger]

It works now. Thank you.