CommandBarPanel

CommandBarPanel

The layout panel behind the Command Bar. It lays its items out in one horizontal row and, when they would run past the available width, collapses whole groups of actions to their single dropdown — lowest CollapseOrder first — so nothing is ever pushed off-screen (INV-054). While the row is wide enough, every group shows its individual Command Icons instead.

• Class: UI.Controls.CommandBarPanel (derives from System.Windows.Controls.Panel)
• Used by: the Command Bar in MainWindow.xaml, in place of the DockPanel it once used.

Authored as a custom layout panel — a Panel subclass with measure/arrange logic, the panel counterpart of a custom Control. It holds no ViewModel and reads no document: collapsing is presentation-only, and the same command runs whether it is reached as an icon or a dropdown entry (INV-054).

How it works

A collapsible group is a pair (or more) of children that share an OverflowGroup name:

• the expanded form — the group's individual buttons (there may be several; their widths add), and
• the collapsed form — a single dropdown, marked IsOverflow="True".

On measure, the panel measures every child at its natural width (regardless of which form is currently shown, so the decision always has each form's true width), then collapses groups by ascending CollapseOrder until the active items fit the available width — less the width reserved for any right-docked item. A child with no OverflowGroup is always shown. Hiding is done with opacity (and hit-testing), not by collapsing layout, so a group that no longer fits disappears cleanly yet can reappear the instant the window grows.

Because the panel re-measures whenever its width changes, the collapse set is a pure function of the available width: the same width always yields the same collapsed groups.

Attached properties

Property	Type	Description
OverflowGroup	string?	Names the group a child belongs to. Children sharing a name are one group; null (the default) means the child is always shown.
IsOverflow	bool	True on the group's collapsed form (its dropdown); False (default) on the expanded form.
CollapseOrder	int	The group's collapse order — lower collapses first. Set the same value on both forms of a group.

The panel also reads the standard DockPanel.Dock attached property: a child with Dock="Right" is laid out against the right edge (the theme toggle), and its width is reserved before any group collapses.

Usage

<controls:CommandBarPanel Margin="8,6">
    <!-- always-shown items … -->

    <!-- a group's expanded form: individual icons -->
    <Button controls:CommandBarPanel.OverflowGroup="Insert" controls:CommandBarPanel.CollapseOrder="1" … />
    <Button controls:CommandBarPanel.OverflowGroup="Insert" controls:CommandBarPanel.CollapseOrder="1" … />

    <!-- the same group's collapsed form: one dropdown -->
    <Menu controls:CommandBarPanel.OverflowGroup="Insert" controls:CommandBarPanel.IsOverflow="True"
          controls:CommandBarPanel.CollapseOrder="1"> … </Menu>

    <Button DockPanel.Dock="Right" … />  <!-- pinned to the right edge -->
</controls:CommandBarPanel>