ArcGIS Pro 3.0 API Reference Guide
ArcGIS.Desktop.Core Namespace / Item Class / OnExpanded Method

OnExpanded Method (Item)
Override to implement any custom logic when your item is expanded
Syntax
public virtual Task OnExpanded()
Requirements

Target Platforms: Windows 11, Windows 10, Windows 8.1

ArcGIS Pro version: 2.8 or higher.
See Also