[lihongfang16]

Problem

When Expander.ExpandDirection is Left or Right, the header is rotated -90° as a whole: the text is arranged vertically, but every glyph lies on its side (you have to tilt your head to read it), and there is no way to control the header text orientation.

Solution

Per review feedback, this uses an attached property instead of Tag: a new hc:ExpanderElement.HeaderTextOrientation (enum ExpanderHeaderTextOrientation: Default / Vertical / Horizontal), defined in Controls/Attach/ExpanderElement.cs following the existing BorderElement pattern. The Left/Right templates name the header ContentPresenter (HeaderText) and add template triggers on the attached property:

HeaderTextOrientation	Header layout
unset (Default)	identical to the current behavior (whole -90° rotation, default unchanged)
Vertical	upright vertical: a +90° counter-rotation cancels the outer -90°, and an injected ContentTemplate makes the TextBlock wrap at one glyph width (FontSize), so characters stand upright and stack top-to-bottom
Horizontal	upright horizontal: only the +90° counter-rotation, a single horizontal line

Notes:

• The arrow (PathArrow) keeps its original -90° rotation and the outer layout geometry is unchanged;
• ExpanderUpTemplate / ExpanderDownTemplate are untouched, so the Up/Down default behavior is unaffected;
• It can be combined with HorizontalContentAlignment to control where the text sits relative to the arrow (Left = away from the arrow (default) / Center = centered / Right = next to the arrow).

Usage

xmlns:hc="clr-namespace:HandyControl.Controls;assembly=HandyControl"

<Expander ExpandDirection="Left" hc:ExpanderElement.HeaderTextOrientation="Vertical" Header="..." />
<Expander ExpandDirection="Left" hc:ExpanderElement.HeaderTextOrientation="Vertical" HorizontalContentAlignment="Center" Header="..." />
<Expander ExpandDirection="Right" hc:ExpanderElement.HeaderTextOrientation="Horizontal" Header="..." />

Verification

• dotnet build src/Net_GE45/HandyControl_Net_GE45/HandyControl_Net_GE45.csproj -f net8.0-windows: 0 warnings, 0 errors;
• the generated combined dictionary Themes/Theme.xaml contains the new triggers;
• verified in a WPF demo app: Left/Right direction × Default/Vertical/Horizontal (six states) plus the three HorizontalContentAlignment combinations all render as expected.

[ghost1372]

@lihongfang16 cant we do this with Attached Properties?

[lihongfang16]

Thanks for the suggestion! Switched to an attached property: hc:ExpanderElement.HeaderTextOrientation (enum ExpanderHeaderTextOrientation: Default / Vertical / Horizontal), defined in Controls/Attach/ExpanderElement.cs following the existing BorderElement pattern. The Tag-based triggers are removed; the default value keeps the current rendering, and it still composes with HorizontalContentAlignment. Pushed as 2d6c4c3.

[ghost1372]

thank you