dotnet/wpf · error

Only one DocumentPageView with IsMasterPage property set to…

Error message

Only one DocumentPageView with IsMasterPage property set to True allowed.

What it means

Among the DocumentPageView objects in a DocumentViewerBase's PageViews collection, exactly one at most may have the attached property IsMasterPage set to true; it designates the master page used for zooming and layout. VerifyDocumentPageViews throws ArgumentException if two or more views declare IsMasterPage=true.

Solutions

1. Ensure only one DocumentPageView has IsMasterPage="True"
2. Remove the IsMasterPage attribute from duplicated views or set it to False
3. Set IsMasterPage programmatically after building the collection, guarding so only the first view gets it

Example fix

// before
<vw:DocumentPageView IsMasterPage="True"/>
<vw:DocumentPageView IsMasterPage="True"/>
// after
<vw:DocumentPageView IsMasterPage="True"/>
<vw:DocumentPageView/>

int masters = pageViews.Cast<DocumentPageView>().Count(pv => DocumentViewerBase.GetIsMasterPage(pv));
if (masters > 1) { /* unset IsMasterPage on all but the first */ }

try { viewer.PageViews = pageViews; }
catch (ArgumentException ex) when (ex.Message.Contains("IsMasterPage")) { /* fix master page flags */ }

When it happens

Trigger: Setting IsMasterPage=true on two or more DocumentPageView instances in the same PageViews collection (in XAML or code) before assigning it to the viewer.

Common situations: Copying a DocumentPageView element in XAML (including its IsMasterPage attribute) to create multiple pages, forgetting to reset IsMasterPage on the copies.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Cannot have empty collection of DocumentPageView objects.
• Bracket characters cannot be alpha-numeric or whitespace.
• Bracket characters cannot be one of the following: '=' …
• DocumentViewer element can have only one child.
• InvalidDrawingAttributesWidth

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/f1ed3f812a9e0c83. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Controls/Primitives/DocumentViewerBase.cs:874

        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.
        }

        /// <summary>
        /// Does deep Visual tree walk to retrieve all DocumentPageViews.
        /// It stops recursing down into visual tree in following situations:
        /// a) Visual is UIElement and it is not part of Contol Template,
        /// b) Visual is DocumentPageView.
        /// </summary>
        /// <param name="root">FrameworkElement that is part of Control Template.</param>
        /// <param name="pageViews">Collection of DocumentPageViews; found elements are appended here.</param>
        /// <returns>Whether collection of DocumentPageViews has been updated.</returns>
        private void FindDocumentPageViews(Visual root, List<DocumentPageView> pageViews)

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