Occurs before a group of items is collapsed.
public event ItemAllowEventHandler GroupCollapsing
The GroupCollapsing event's data class is ItemAllowEventArgs. The following properties provide information specific to this event:
The GroupCollapsing event is raised before a group of data items is collapsed from UI or code (CollapseGroup). You can handle this event and set its parameter's Allow property to false to prevent a group from being collapsed.
When you call the CollapseAllGroups method, the GroupCollapsing event is raised for each group.
After a group has been collapsed, the GroupCollapsed event is raised.