Cannot have empty collection of DocumentPageView objects.

Error message

Cannot have empty collection of DocumentPageView objects.

What it means

DocumentViewerBase.VerifyDocumentPageViews requires a non-empty collection of DocumentPageView objects to build the viewer's page views. A null or empty PageViews collection is invalid because the viewer cannot render any pages without at least one view.

Solutions

Add at least one DocumentPageView to the PageViews collection
If PageViews is data-bound, ensure the source collection is populated before assignment
If the viewer should be empty, avoid setting PageViews at all rather than assigning an empty collection

Example fix

// before
documentViewer.PageViews = new DocumentPageViewList();
// after
documentViewer.PageViews = new DocumentPageViewList { new DocumentPageView() };

Defensive patterns

Strategy: validation

Validate before calling

if (pageViews == null || pageViews.Count == 0) throw new InvalidOperationException("At least one DocumentPageView is required before assigning PageViews.");

Try / catch

try { viewer.PageViews = pageViews; }
catch (ArgumentException ex) when (ex.Message.Contains("DocumentPageView")) { /* supply a non-empty collection */ }

Prevention

Validate PageViews is non-empty before assignment
In XAML, always include at least one DocumentPageView inside PageViews
Guard data-bound collections so they are populated before binding

When it happens

Trigger: Assigning a null or empty DocumentPageViewList to DocumentViewerBase.PageViews (e.g. via XAML <DocumentViewer.PageViews/> or code), which triggers UpdatePageViews -> VerifyDocumentPageViews.

Common situations: Declaratively defining a DocumentViewer with no PageViews in XAML, clearing the PageViews collection at runtime, or data-binding an empty collection into PageViews.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/ea9818f8087dca29. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Primitives/DocumentViewerBase.cs:864

            }
        }

        /// <summary>
        /// Verify collection of DocumentPageViews. It needs to meet following conditions:
        /// a) collection is not null,
        /// b) only one page has IsMasterPage property set to true,
        /// c) unique PageNumbers for each active DocumentPageView,
        /// </summary>
        /// <param name="pageViews">Collection of DocumentPageViews to validate.</param>
        private void VerifyDocumentPageViews(ReadOnlyCollection<DocumentPageView> pageViews)
        {
            int index;
            bool hasMasterPage = false;

            // At least one DocumentPageView is required.
            if (pageViews == null)
            {
                throw new ArgumentException(SR.DocumentViewerPageViewsCollectionEmpty);
            }

            // Expecting only one DocumentPageView with IsMasterPage property set to true.
            for (index = 0; index < pageViews.Count; index++)
            {
                if (GetIsMasterPage(pageViews[index]))
                {
                    if (hasMasterPage)
                    {
                        throw new ArgumentException(SR.DocumentViewerOneMasterPage);
                    }
                    hasMasterPage = true;
                }
            }

            // Unique PageNumbers for each active DocumentPageView.
        }

View on GitHub (pinned to 81131a70a4)