[ecfisa]

Hola.

Podes evaluar el valor de al propiedad QRPrinter.Destination en el evento BeforePrint, vgr.:

Código Delphi [-]
...
implementation

uses qrprntr;

procedure TForm1.QuickRep1BeforePrint(Sender: TCustomQuickRep; var PrintReport: Boolean);
var
  qr: TQuickRep;
begin
  qr := TQuickRep(Sender);

  if qr.QRPrinter.Destination = qrdMetafile then
    ShowMessage('PREVIEW')
  else if qr.QRPrinter.Destination = qrdPrinter then
    ShowMessage('PRINT');
end;
...

Saludos