NullReferenceException thrown by GetPrintJobInfoCollection() when trying to get the print jobs from default printer

Question

I am trying to display the print jobs currently in print queue of a default printer on the console using this code:

for (;;)
{
    string printerName = new System.Drawing.Printing.PrinterSettings().PrinterName;
    System.Printing.LocalPrintServer localPrintServer = new System.Printing.LocalPrintServer();
    System.Printing.PrintQueueCollection printQueues = localPrintServer.GetPrintQueues(new[] { System.Printing.EnumeratedPrintQueueTypes.Local, System.Printing.EnumeratedPrintQueueTypes.Connections });

    if (printQueues == null) return;

    System.Printing.PrintQueue queue = printQueues.Where(x => x.Name.Equals(printerName)).FirstOrDefault();
    if (queue.NumberOfJobs <= 0)
        Console.WriteLine("Queue Empty!");
    else
    {
        Console.WriteLine("Number of Jobs: " + queue.NumberOfJobs);
        foreach (System.Printing.PrintSystemJobInfo psji in queue.GetPrintJobInfoCollection())
        {
            Console.WriteLine(psji.Name);
        }
        Console.WriteLine("\n\nPress any key to exit...");
        Console.ReadLine();
        break;
    }
}

When there is no item in the print queue it succesfully displays "Queue Empty!".

But when I start document printing, NumberOfJobs=1 but GetPrintJobInfoCollection() throws NullReferenceException.

Why there is a job and still its returning null?

What can be the reason?

Also, I don't have a printer so I am trying to print it on "Microsoft Print to PDF".

Also its not a duplicate of the question @PatrickHofman mentioned. I know why `NullReferenceException` is thrown. But my question is why that function is throwing even there is data in the collection. Please remove Duplicate flag. — Aishwarya Shiva, Jun 27 '17 at 10:50
At least give us some information to start with. What is the exact call stack? Is it a multi-threaded application? Where does that code run? — Patrick Hofman, Jun 27 '17 at 10:53
@PatrickHofman it's a simple console application and this is the complete code. — Aishwarya Shiva, Jun 27 '17 at 10:54
And you are sure that `GetPrintJobInfoCollection()` is throwing the exception and not for example `psji`? — Patrick Hofman, Jun 27 '17 at 10:56
`psji` is an element in the collection returned by `GetPrintJobInfoCollection()`. But why that collection is `null` if `NumberOfJobs=1`? This is what I am asking. — Aishwarya Shiva, Jun 27 '17 at 10:57
So is the collection null? Then you know the reason the code fails and you actually want to ask another question... — Patrick Hofman, Jun 27 '17 at 10:58
@PatrickHofman The question is why it is `null`. Even if the count>0. — Aishwarya Shiva, Jun 27 '17 at 10:59
But that is not the question you are asking. You are asking why you get the exception. The answer: because it is null. Why it is null is another question. — Patrick Hofman, Jun 27 '17 at 11:00
https://msdn.microsoft.com/en-us/library/system.printing.printqueue.getprintjobinfocollection(v=vs.110).aspx suggests you should refresh the queue before issuing the getprintjobinfocollection — BugFinder, Jun 27 '17 at 11:03
@BugFinder Thanks a lot it worked. I hope someone will reopen this question and please add this as an answer. Because this might be helpful in future to someone else. — Aishwarya Shiva, Jun 27 '17 at 11:07
@PatrickHofman maybe able to reopen it, I've added my vote.. — BugFinder, Jun 27 '17 at 11:11
@AishwaryaShiva ping me if it gets reopeed, I'll add it as an answer.. so you can record it properly — BugFinder, Jun 27 '17 at 11:11
@PatrickHofman I asked **Why there is a job and still its returning null? What can be the reason?** I think that clears the confusion. Please see BugFinder answer and reopen it. — Aishwarya Shiva, Jun 27 '17 at 11:12

score 5 · Accepted Answer · answered Jun 27 '17 at 11:31

If you look at the Microsoft link it shows that it refreshes the queue before asking for the GetPrintJobInfoCollection.

While, it would seem logical that you only just grabbed the queue how out of date can it be, the fact their example specifically refreshes would suggest this is the way to go.

NullReferenceException thrown by GetPrintJobInfoCollection() when trying to get the print jobs from default printer

1 Answers1