Collapsible

Overview

Collapsible is a lookless ContentControl root (NaviusCollapsible) that owns a single Open boolean and discovers its NaviusCollapsibleTrigger/NaviusCollapsiblePanel descendants through the logical tree, the same “root owns state, discovers descendants” shape as NaviusAccordion and NaviusRadioGroup. WPF’s native Expander was rejected as a base because it fuses header and content into one control and cannot preserve the contract’s separately addressable Trigger/Panel parts.

Usage

xmlns:navius="clr-namespace:Navius.Wpf.Primitives.Controls;assembly=Navius.Wpf.Primitives"
xmlns:collapsible="clr-namespace:Navius.Wpf.Primitives.Controls.Collapsible;assembly=Navius.Wpf.Primitives"

<collapsible:NaviusCollapsible x:Name="Details">
    <StackPanel>
        <collapsible:NaviusCollapsibleTrigger Content="Show details" />
        <collapsible:NaviusCollapsiblePanel>
            <TextBlock Text="Hidden content revealed when open." />
        </collapsible:NaviusCollapsiblePanel>
    </StackPanel>
</collapsible:NaviusCollapsible>

Properties

Property	Type	Default	From	Description
Open	bool	false	NaviusCollapsible	Open/closed state. Bindable via standard WPF binding; OpenChanged fires on every change.
IsPanelOpen	bool	false	NaviusCollapsibleTrigger	Mirrors Open; set by the ancestor NaviusCollapsible, not by the trigger itself.
IsOpen	bool	false	NaviusCollapsiblePanel	Mirrors Open; set by the ancestor NaviusCollapsible.
KeepMounted	bool	false	NaviusCollapsiblePanel	Keeps Content cached and only toggles Visibility instead of clearing Content on close.
Content	object	-	ContentControl	Body content on the root, Trigger, and Panel.

Events

Event	Signature	Fires when
OpenChanged	RoutedEventHandler	Open changes (a trigger click or a direct Open write).

Keyboard interactions

Key	Behavior
Space / Enter	Toggles the panel; native Button.Click behavior on the focused NaviusCollapsibleTrigger, no custom key handler.

UIA mechanism

NaviusCollapsibleAutomationPeer reports AutomationControlType.Group on the root and carries no expand/collapse state of its own, matching the contract’s asymmetry where the root exposes no data-* state attribute at all. NaviusCollapsibleTriggerAutomationPeer reports AutomationControlType.Button and implements both IInvokeProvider (native Button behavior) and IExpandCollapseProvider (ExpandCollapseState from IsPanelOpen), the same dual-pattern shape WPF’s own ExpanderAutomationPeer uses. CollapsibleTests.cs exercises the root-owns-state shape, the dual trigger patterns, and the IsEnabled cascading described below.

Web deltas

• HiddenUntilFound (the web’s browser in-page-find integration) is dropped entirely; there is no WPF “find in page” affordance to hook a reveal callback into.
• WPF’s IsEnabled does not automatically cascade through a ContentControl’s logical Content; SyncDescendants explicitly pushes it onto the Trigger, matching “Disabled blocks toggling.”
• The enter/exit height transition is a plain DoubleAnimation via a shared PanelHeightAnimator helper (also used by NaviusAccordionPanel), not the web’s JS-measured natural-size CSS variables or two-phase “starting-style” mount frame; Height animates from a hard 0 instead.
• Logical open/closed state (Open, IsPanelOpen, IsOpen, and the peer’s ExpandCollapseState) flips synchronously and independently of the animation clock, so it stays correct in a headless test host where nothing pumps the animation to completion; only the cosmetic Height/Visibility transition is asynchronous.
• KeepMounted=false (default) additionally caches and clears Content once the close animation’s Completed callback fires, approximating DOM removal; the web’s KeepMounted only toggles visibility/hidden state, since Blazor content isn’t cached/cleared the same way.

Captures

The Collapsible Gallery page rendered at the pinned commit, in each theme.