Invalidates the specified region of the control (adds it to the control's update region, which is the area that will be repainted at the next paint operation), and causes a paint message to be sent to the control. Optionally, invalidates the child controls assigned to the control.

'Declaration
 
Public Overloads Sub Invalidate( _
   ByVal region As Region, _
   ByVal invalidateChildren As Boolean _
) 

public void Invalidate( 
   Region region,
   bool invalidateChildren
)