OnDragOver event dispatcher.
function DragOver(Sender: TObject; Source: TObject; X: Integer; Y: Integer; State: TDragState): Boolean; virtual;
Override DragOver to add additional code that executes before the OnDragOver event handler is called.
DragOver sets the Accept parameter to true to indicate that the user can drop the dragged object on the control. It sets Accept to false to indicate that the user cannot drop the dragged object on the control.
The Source parameter is the object being dragged. The State parameter indicates how the dragged object is moving in relation to the control. X and Y indicate the current position of the mouse.