dotnet/wpf · error · ArgumentNullException

queue

Error message

queue

What it means

The PrintContext constructor throws ArgumentNullException with parameter name "queue" when a null PrintQueue is passed. A print context is meaningless without a target print queue — it is used to open the print document stream (StartDoc/EndDoc), so the queue is a mandatory dependency.

Solutions

1. Validate the PrintQueue before constructing PrintContext and surface a user-facing 'select a printer' message
2. Resolve the queue explicitly: new PrintContext(GetValidQueue()) and fail early with a clear error if null
3. Handle the case where the selected printer no longer exists by re-enumerating LocalPrintServer.GetPrintQueues

Example fix

// before
var ctx = new PrintContext(dialog.PrintQueue); // null if user never picked a printer
// after
if (dialog.PrintQueue == null) { ShowSelectPrinterDialog(); return; }
var ctx = new PrintContext(dialog.PrintQueue);

if (queue == null)
    throw new InvalidOperationException("A print queue must be selected before printing.");

try { var ctx = new PrintContext(queue); }
catch (ArgumentNullException ex) when (ex.ParamName == "queue") { ShowSelectPrinterDialog(); }

When it happens

Trigger: new PrintContext(null) — typically when the PrintQueue came from a failed lookup (LocalPrintServer.GetPrintQueue returning null), an unresolved variable, or a PrintDialog whose PrintQueue was never assigned.

Common situations: Print-queue selection UI where no printer was chosen; print-server enumeration returning a missing queue; deserializing saved print settings referencing a removed printer.

Related errors

• getPage
• PrintSystemException.PrintSystemJobInfo.Create
• value
• visual
• annotation component

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/2af144589db48b2b. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/printcontext.cs:186

            }
        }
    }

    #region public class PrintContext
    /// <summary>
    /// PrintContext provides visual level printing API
    /// </summary>
    public class PrintContext : DispatcherObject
    {
        /// <summary>
        /// Connect to a specified print queue
        /// </summary>
        /// <param name="queue"></param>
        public PrintContext(PrintQueue queue)
        {
            if( queue == null )
            {
               throw new ArgumentNullException("queue");
            }

            // enter batching for printing
            MediaContext.CurrentMediaContext.ChannelSyncMode = true;

            _queue     = queue;
            _jobTicket = new JobTicket(queue.UserJobTicket); // Make a new copy
        }

        #region Print()
        /// <summary>
        /// Print a job
        /// </summary>
        public void Print(GetPageCallback getPage, string jobName)
        {
            try
            {
                if (getPage == null)

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