dotnet/wpf · error · ArgumentException

SR.NotInAssociatedTree

Error message

SR.NotInAssociatedTree

What it means

ValidationHelper.VerifyPosition throws ArgumentException(SR.NotInAssociatedTree) when the supplied position belongs to a different ITextContainer than the one passed in. TextPointers are only valid within their owning document; mixing pointers between documents is rejected.

Solutions

1. Always obtain pointers from the same container you operate on (e.g. use document.ContentStart of THAT document).
2. Re-create pointers after swapping the control's Document; old pointers are orphaned.
3. Guard with pos.TextContainer == container before calling text APIs.

Example fix

// before
otherDoc.TextContainer.VerifyPosition(container, pointerFromOtherDoc, nameof(pointerFromOtherDoc));
// after
if (pointerFromOtherDoc.TextContainer == container) container.VerifyPosition(container, pointerFromOtherDoc, nameof(pointerFromOtherDoc));

bool sameTree = position != null && position.TextContainer == container;

bool BelongsToContainer(ITextPointer p, ITextContainer c) => p != null && p.TextContainer == c;

try { container.VerifyPosition(container, pos, nameof(pos)); }
catch (ArgumentException) { pos = container.CurrentPosition; }

When it happens

Trigger: Passing a TextPointer from one FlowDocument/TextBox to another document's API (e.g. container.VerifyPosition(otherContainer, pointerFromElsewhere, nameof(pos))).

Common situations: Copying TextPointer fields between RichTextBox instances; using a saved pointer after assigning a new FlowDocument to the control; merging selections from two documents.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• SR.AnnotationAdorner_NotUIElement
• SR.AudioVideo_InvalidDependencyObject
• SR.Format(SR.BadFixedTextPosition, "position")
• SR.Format(SR.CannotConvertType, key.GetType(), "int")
• SR.Format(SR.CannotConvertType, typeof(CharacterMetrics)…

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/507349e52d38ed29. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Documents/ValidationHelper.cs:44

        // Throws an appropriate exception if a test fails.
        internal static void VerifyPosition(ITextContainer tree, ITextPointer position)
        {
            VerifyPosition(tree, position, nameof(position));
        }
        
        // Verifies a TextPointer is non-null and is associated with a given TextContainer.
        //
        // Throws an appropriate exception if a test fails.
        internal static void VerifyPosition(ITextContainer container, ITextPointer position, string paramName)
        {
            if (position == null)
            {
                throw new ArgumentNullException(paramName);
            }

            if (position.TextContainer != container)
            {
                throw new ArgumentException(SR.Format(SR.NotInAssociatedTree, paramName));
            }
        }

        // Verifies two positions are safe to use as a logical text span.
        //
        // Throws ArgumentNullException if startPosition == null || endPosition == null
        //        ArgumentException if startPosition.TextContainer != endPosition.TextContainer or
        //                             startPosition > endPosition
        internal static void VerifyPositionPair(ITextPointer startPosition, ITextPointer endPosition)
        {
            ArgumentNullException.ThrowIfNull(startPosition);
            ArgumentNullException.ThrowIfNull(endPosition);
            if (startPosition.TextContainer != endPosition.TextContainer)
            {
                throw new ArgumentException(SR.Format(SR.InDifferentTextContainers, "startPosition", "endPosition"));
            }
            if (startPosition.CompareTo(endPosition) > 0)
            {

View on GitHub (pinned to 81131a70a4)