/// <summary>
/// Initializes all fields in the print job monitor.
/// </summary>
private void Initialize()
{
// In the event that the monitor is started while the spooler is offline,
// keep retrying until the spooler becomes available.
SafePrinterHandle hPrinter = null;
while (true)
{
try
{
void action() => hPrinter = OpenPrinter(null);
Retry.WhileThrowing <Win32Exception>(action, 5, TimeSpan.FromSeconds(30));
break;
}
catch (Win32Exception ex)
{
switch (ex.NativeErrorCode)
{
// Ignore these errors.
case RPC_S_SERVER_UNAVAILABLE:
case RPC_S_CALL_FAILED:
case ERROR_INVALID_PRINTER_NAME:
Thread.Sleep(TimeSpan.FromSeconds(1));
break;
default:
throw;
}
}
}
_options = CreatePrinterNotifyOptions();
SafePrinterChangeNotificationHandle hChange = FindFirstPrinterChangeNotification(hPrinter, PrinterChanges.Job, _options);
_hPrinters.Add(hPrinter);
_hChanges.Add(hChange);
}
internal static extern bool FindNextPrinterChangeNotification(SafePrinterChangeNotificationHandle hChange, [Out] out uint pdwChange, ref PrinterNotifyOptions pPrinterNotifyOptions, [Out] out SafePrinterNotifyInfoHandle ppPrinterNotifyInfo);
internal static extern SafePrinterChangeNotificationHandle FindFirstPrinterChangeNotification(SafePrinterHandle hPrinter, uint printerChanges, uint fdwOptions, ref PrinterNotifyOptions pPrinterNotifyOptions);
/// <summary>
/// Retrieves information about the most recent notification for a change notification object associated with a printer or print server.
/// Call this function when a wait operation on the change notification object is satisfed.
/// </summary>
/// <param name="hChange">A handle to a change notification object associated with a printer or print server.</param>
/// <param name="options">The <see cref="PrinterNotifyOptions" />.</param>
/// <returns>A <see cref="PrinterNotifyInfoReader" /> containing the notification details.</returns>
/// <exception cref="Win32Exception">The underlying operation failed.</exception>
/// <exception cref="System.Exception">
/// No notification available at this time.
/// or
/// Info has been discarded.
/// </exception>
private static PrinterNotifyInfoReader FindNextPrinterChangeNotification(SafePrinterChangeNotificationHandle hChange, PrinterNotifyOptions options = new PrinterNotifyOptions())
{
if (!NativeMethods.FindNextPrinterChangeNotification(hChange, out _, ref options, out SafePrinterNotifyInfoHandle infoHandle))
{
throw new Win32Exception();
}
if (infoHandle == null || infoHandle.IsInvalid)
{
// Apparently there was no notification after all. Just return an empty reader.
return(new PrinterNotifyInfoReader());
}
PrinterNotifyInfoReader result = new PrinterNotifyInfoReader(infoHandle);
// Check to see if data has been discarded.
if (result.InfoDiscarded)
{
result.Dispose();
return(null);
}
return(result);
}
/// <summary>
/// Creates a change notification object and returns a handle to the object.
/// </summary>
/// <param name="hPrinter">A handle to the printer or print server to monitor.</param>
/// <param name="filter">The <see cref="PrinterChanges" /> that should trigger new events.</param>
/// <param name="options">The <see cref="PrinterNotifyOptions" /> that dictate which notifications should be sent.</param>
/// <returns>A handle to a change notification object associated with the specified printer or print server.</returns>
/// <exception cref="Win32Exception">The underlying operation failed.</exception>
private static SafePrinterChangeNotificationHandle FindFirstPrinterChangeNotification(SafePrinterHandle hPrinter, PrinterChanges filter, PrinterNotifyOptions options)
{
uint fdwOptions = 0; // Must always be zero for 2D printers.
SafePrinterChangeNotificationHandle result = NativeMethods.FindFirstPrinterChangeNotification(hPrinter, (uint)filter, fdwOptions, ref options);
if (Marshal.GetLastWin32Error() > 0)
{
throw new Win32Exception();
}
return(result);
}
