PanelColumn

PanelColumn

The attached behaviour that owns a Panel Column's width — the Workspace grid column holding a toggleable panel. While its panel is shown the column takes the width the user last dragged its Panel Splitter to (or VisibleWidth until it has been dragged); while its panel is hidden — Closed or Auto-Hidden — the column takes no width at all, so the Visual Document fills the whole Workspace (INV-056, INV-062). A fill column instead takes the editing area's remaining width while shown: the primary Document Pane's column — the Editor Pane's always, and the Source Panel's exactly while the Editor Pane is not Docked (INV-063).

• Class: UI.Controls.PanelColumn — a static attached-property behaviour targeting ColumnDefinition.
• Used by: MainWindow.xaml on the editing grid's Editor, Source, and Preview columns.

How it works

The width cannot be projected from the visibility flag by a converter alone: dragging a GridSplitter writes the column's Width directly, and a direct write replaces a one-way binding — after the first drag the binding is gone, and hiding the panel would leave the dragged-open column behind. Owning both the toggle and the remembered drag in one behaviour keeps the two from fighting. The minimum bounds the splitter, not the toggle: a hidden column gives up its minimum along with its width, so it truly collapses. A pixel width is remembered whenever the behaviour replaces it (on hiding, or on becoming the fill column), so showing the panel again — or handing the fill role back — restores the dragged width; a star width is never remembered.

Attached properties

Property	Type	Default	Description
IsVisible	bool?	null	Whether the column's panel is shown. Hidden ⇒ zero width, zero minimum.
VisibleWidth	double	380	The width the panel opens at before it has been dragged.
MinimumWidth	double	180	The narrowest a Panel Splitter may drag the shown panel.
Fill	bool	false	Fill column: shown, it takes the remaining width (star) at MinimumWidth instead of a remembered pixel width (INV-063).

Usage

<Grid.ColumnDefinitions>
    <!-- The Editor Pane: fills while Docked, collapses entirely while not (INV-063). -->
    <ColumnDefinition controls:PanelColumn.Fill="True"
                      controls:PanelColumn.MinimumWidth="240"
                      controls:PanelColumn.IsVisible="{Binding IsEditorPaneVisible}" />
    <ColumnDefinition Width="Auto" />
    <!-- The Source Panel: a dragged-width panel that fills while it is the primary Document Pane. -->
    <ColumnDefinition controls:PanelColumn.VisibleWidth="420"
                      controls:PanelColumn.Fill="{Binding IsSourcePanelPrimary}"
                      controls:PanelColumn.IsVisible="{Binding IsSourcePanelVisible}" />
</Grid.ColumnDefinitions>

Styling

None — the behaviour writes layout (Width/MinWidth) only and draws nothing.