Question

How can my Delphi component detect at design time if any other component is being dropped on the form?

Answer 1

You should override Notification method of your component; something like that:

type
  TMyComponent = class(TComponent)
//..
  protected
    procedure Notification(AComponent: TComponent;
      Operation: TOperation); override;
  end;


procedure TMyComponent.Notification(AComponent: TComponent;
  Operation: TOperation);
begin
  inherited Notification(AComponent, Operation);
  if (Operation = opInsert) and (csDesigning in ComponentState) then begin
// AComponent was dropped on the form
  end;
end;