How to show printer properties/preferences dialog and save changes?

Question

EDIT: My fault! I expected the changes to be written back to the default printer settings when in fact only the local instance of the PrinterSettings are changed. -

Answer 1

Even though the answer ended up working its way into the question, I think the following provides a better answer to the original question,

(1) Because it clearly does not modify the passed-in PrinterSettings if the user cancels.

(2) Because it returns a DialogResult, which the caller will likely be interested in.

[DllImport("kernel32.dll")]
static extern IntPtr GlobalLock(IntPtr hMem);
[DllImport("kernel32.dll")]
static extern bool GlobalUnlock(IntPtr hMem);
[DllImport("kernel32.dll")]
static extern bool GlobalFree(IntPtr hMem);
[DllImport("winspool.Drv", EntryPoint = "DocumentPropertiesW", SetLastError = true, ExactSpelling = true, CallingConvention = CallingConvention.StdCall)]
static extern int DocumentProperties(IntPtr hwnd, IntPtr hPrinter, [MarshalAs(UnmanagedType.LPWStr)] string pDeviceName, IntPtr pDevModeOutput, IntPtr pDevModeInput, int fMode);

private const int DM_PROMPT = 4;
private const int DM_OUT_BUFFER = 2;
private const int DM_IN_BUFFER = 8;

private DialogResult EditPrinterSettings(PrinterSettings printerSettings)
{
    DialogResult myReturnValue = DialogResult.Cancel;
    IntPtr hDevMode = printerSettings.GetHdevmode(printerSettings.DefaultPageSettings);
    IntPtr pDevMode = GlobalLock(hDevMode);
    int sizeNeeded = DocumentProperties(this.Handle, IntPtr.Zero, printerSettings.PrinterName, pDevMode, pDevMode, 0);
    IntPtr devModeData = Marshal.AllocHGlobal(sizeNeeded);
    long userChoice = DocumentProperties(this.Handle, IntPtr.Zero, printerSettings.PrinterName, devModeData, pDevMode, DM_IN_BUFFER | DM_PROMPT | DM_OUT_BUFFER);
    long IDOK = (long)DialogResult.OK;
    if (userChoice == IDOK)
    {
        myReturnValue = DialogResult.OK;
        printerSettings.SetHdevmode(devModeData);
        printerSettings.DefaultPageSettings.SetHdevmode(devModeData);
    }
    GlobalUnlock(hDevMode);
    GlobalFree(hDevMode);
    Marshal.FreeHGlobal(devModeData);
    return myReturnValue;
}