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type
  TQRCustomPreviewInterface = class(TQRPreviewInterface)
  private
    { Private declarations }
  public
    { Public declarations }
    function Show(aQRPrinter: TQRPrinter): TWinControl; override;
    function ShowModal(aQRPrinter: TQRPrinter): TWinControl; override;
  end;

type
  TCustomPreview = class(TForm)
    QRPreview1: TQRPreview;
    ...
    procedure FormShow(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure FormCloseQuery(Sender: TObject; var CanClose: Boolean);
    procedure QRPreview1PageAvailable(Sender: TObject; PageNum: Integer);
  private
    { Private declarations }
    fQRPrinter: TQRPrinter;
    constructor Create(aQwner: TComponent; aQRPrinter: TQRPrinter); virtual;
    ...
  public
    { Public declarations }
  end;

...

function TQRCustomPreviewInterface.Show(aQRPrinter: TQRPrinter): TWinControl;
var frm: TCustomPreview;
begin
  Result := TCustomPreview.Create(Application, aQRPrinter);
  TCustomPreview(Result).Show;
end;

function TQRCustomPreviewInterface.ShowModal(aQRPrinter: TQRPrinter): TWinControl;
begin
  Result := TCustomPreview.Create(Application, aQRPrinter);
  TCustomPreview(Result).ShowModal;
end;

...

constructor TCustomPreview.Create(aQwner: TComponent; aQRPrinter: TQRPrinter);
begin
  inherited Create(aQwner);
  fQRPrinter := aQRPrinter;
  QRPreview1.QRPrinter := aQRPrinter;
end;

procedure TCustomPreview.FormCloseQuery(Sender: TObject; var CanClose: Boolean);
begin
  if QRPreview1.QRPrinter.Status = mpBusy then
  begin
    CanClose := false;
    ShowMessage(StrCustomPreviewUnDone); //busy
  end
  else CanClose := true;
end;

procedure TCustomPreview.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  ...
  fQRPrinter.ClosePreview(self);
  action := caFree;
end;

procedure TCustomPreview.FormShow(Sender: TObject);
begin
  ... //controls setup in form
end;

...

initialization
  RegisterPreviewClass(TQRCustomPreviewInterface);
end.