You will want to use System.Windows.Forms.HandledMouseEventArgs primarily when developing a control that needs to handle mouse wheel events itself, and prevent them from being seen by the control's immediate parent container. System.Windows.Forms.HandledMouseEventArgs is not passed directly by System.Windows.Forms.MouseEventHandler when it handles the Control.MouseWheel event. Rather, System.Windows.Forms.MouseEventHandler uses a System.Windows.Forms.MouseEventArgs, which you must cast to a System.Windows.Forms.HandledMouseEventArgs in order to cancel an occurrence of Control.MouseWheel.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
Assembly Versions: 2.0.0.0
Since: .NET 2.0