C# Cannot Print using PrintDialog when changing print properties after ShowDialog()

Question

The issue occurs when i am using ShowDialog() before setting the Print page properties of my WPF Control (Height ,width ,Number of pages) and then calling PrintDocument() with the desired document, the result of those steps is an empty page printed.

BUT when I'm doing those steps VICE VERSA (setting the Print page properties BEFORE calling ShowDialog) it works. But that's not the desired flow, because i want the user to be able to change the selected printer before I'm setting the print page properties.

How can i solve this issue?

   void OnIMSendToPrint(object objId, object data)
    {
        PrintDialog printDialog = new PrintDialog();
        if (printDialog.ShowDialog().Value != true) return;

        CheckPrinterPaperType(printDialog);  // Determine the type of the choosen printer , and the paper type.
        PreparePrintVM(); // Prepare the wpf control to print accord to the paper and print type

        if (mainView != null
            && mainView.PrintScreenView != null
            && mainView.PrintScreenView.flowDocument != null
            )
        {
            int extraWidth = -10;
            if (CurrentPrinterPaperType == PrinterPaperSize.Small) extraWidth = 690;
            mainVM.PrintScreen.SetPageSize(printDialog.PrintableAreaWidth + extraWidth,
                printDialog.PrintableAreaHeight);
            printDialog.PrintDocument(((IDocumentPaginatorSource)(mainView.PrintScreenView.flowDocument))
                .DocumentPaginator, "This is a Flow Document");
        }
    }


   private void CheckPrinterPaperType(PrintDialog printDialog)
    {
        CurrentPrinterPaperType = printDialog.PrintableAreaWidth >= 595 && printDialog.PrintableAreaHeight >=792
            ? PrinterPaperSize.Large
            : PrinterPaperSize.Small;
    }

 private void PreparePrintVM()
    {
        PrintScreenVM newPrintScreen = new PrintScreenVM();
        int NumOfColumsInPrintPage = ScResMgr.GetValue("ImageManager", "NumOfColumsInPrintPage", 2);
        int NumOfRowsInPrintPage = ScResMgr.GetValue("ImageManager", "NumOfRowsInPrintPage", 4);
        int imagesNumPerPage = NumOfColumsInPrintPage * NumOfRowsInPrintPage;
        if (CurrentPrinterPaperType == PrinterPaperSize.Small) imagesNumPerPage = 1;

        foreach (SeriesVM seriesVM in mainVM.Patient.Series)
        {
            List<ImageVM> selectedImageList = seriesVM.GetSelectedImages();
            foreach (ImageVM image in selectedImageList)
                image.LoadImage(true);

            for (int i = 0; i < selectedImageList.Count; i += imagesNumPerPage)
            {
                int numOfImages = (i + imagesNumPerPage > selectedImageList.Count) ? selectedImageList.Count - i : imagesNumPerPage;
                newPrintScreen.AddPage(
                    mainVM.Patient.FirstName,
                    mainVM.Patient.LastName,
                    mainVM.Patient.PatientId,
                    seriesVM.DateTime,
                    selectedImageList.GetRange(i, numOfImages),
                    NumOfColumsInPrintPage,
                    NumOfRowsInPrintPage);
            }
        }
        mainVM.PrintScreen = newPrintScreen;

    }