By default, the SplitContainer.OnMouseMove(MouseEventArgs) event handler allows the user to track the splitter position while it is moved with the mouse. SplitContainer.OnMouseMove(MouseEventArgs) also draws the SplitContainer.SplitterRectangle to show the current position of the splitter while it is moving. The System.Windows.Forms.SplitContainer keeps track of the initial SplitContainer.SplitterDistance in case the user cancels the move.

Raising an event invokes the event handler through a delegate. For more information, see Raising an Event.

The SplitContainer.OnMouseMove(MouseEventArgs) method also allows derived classes to handle the event without attaching a delegate. This is the preferred technique for handling the event in a derived class.