ArcGIS Pro 2.6 API Reference Guide
OnHidden Method (DockPane)

ArcGIS.Desktop.Framework.Contracts Namespace > DockPane Class : OnHidden Method
Called when the DockPane is completely hidden.
Syntax
protected internal virtual void OnHidden()
Protected Friend Overridable Sub OnHidden() 
Remarks
DockPanes are singletons and pushing their Close button really just hides them.
Requirements

Target Platforms: Windows 10, Windows 8.1, Windows 7

See Also

Reference

DockPane Class
DockPane Members