dotnet/wpf · error · ArgumentNullException

getPage

Error message

getPage

What it means

PrintContext.Print throws ArgumentNullException with parameter name "getPage" when the GetPageCallback delegate is null. Print iterates pages by invoking this callback, so without it no pages can be produced.

Solutions

1. Ensure a non-null GetPageCallback (e.g. a method that returns each page's Visual) before calling Print
2. Validate the delegate early and report a configuration error instead of crashing at print time
3. Combine with XpsDocumentWriter/PrintDialog flows that guarantee a callback is supplied

Example fix

// before
context.Print(null, "Job"); // throws
// after
GetPageCallback cb = (pageNumber) => RenderPage(pageNumber);
context.Print(cb, "Job");

if (getPage == null)
    throw new InvalidOperationException("A GetPageCallback must be supplied to print.");

try { context.Print(getPage, jobName); }
catch (ArgumentNullException ex) when (ex.ParamName == "getPage") { Log("Page-render callback missing"); }

When it happens

Trigger: Calling printContext.Print(null, jobName) — e.g. when the delegate was built conditionally and never assigned, or a method group reference resolved to null after refactoring.

Common situations: Custom print pipelines where the page-content provider is constructed asynchronously and not ready at Print time; refactoring that removed the page-rendering method while keeping the Print call.

Related errors

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

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/96549ac9814defea. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/printcontext.cs:206

            // 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)
                {
                    throw new ArgumentNullException("getPage");
                }

                this.StartDoc(jobName);

                int pageNo = 0;

                Visual visual = getPage(this);

                while (!_cancel && (visual != null))
                {
                    string uri = this.StartPage(pageNo);

                    this.Render(visual, uri);
                    this.EndPage();

                    pageNo++;

                    visual = getPage(this);

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