dotnet/wpf · error · ArgumentException

SR.WrongSelectionType

Error message

SR.WrongSelectionType (selection: type={selection.GetType()})

What it means

CheckSelection validates that the selection object handed to the processor is a TextAnchor or TextSelection whose start TextContainer is a FixedTextContainer or DocumentSequenceTextContainer. Otherwise it throws ArgumentException(SR.WrongSelectionType) with the actual runtime type. Called from GenerateLocatorParts and textSegments.

Solutions

1. Only pass selections created from DocumentPageView/FixedPage content (FixedTextContainer).
2. Use the TextSelectionProcessor subclass that matches the content type (Fixed vs tree).
3. Check selection is ITextSelection/TextAnchor and its TextContainer type before calling.

Example fix

// before
processor.GenerateLocatorParts(unknownSelection); // may be a flow selection
// after
if (sel is TextSelection ts && (ts.Start.TextContainer is FixedTextContainer || ts.Start.TextContainer is DocumentSequenceTextContainer))
    processor.GenerateLocatorParts(ts);

if (!(selection is TextSelection || selection is TextAnchor)) throw new InvalidOperationException("selection must be TextSelection or TextAnchor");

bool IsFixedSelection(object s) => s is TextSelection ts && (ts.Start.TextContainer is FixedTextContainer || ts.Start.TextContainer is DocumentSequenceTextContainer);

try { processor.GenerateLocatorParts(selection); } catch (ArgumentException ex) { /* wrong selection type — re-derive from page view */ }

When it happens

Trigger: Calling GenerateLocatorParts (or the textSegments helper) with a selection that is neither TextAnchor nor TextSelection (first throw), or whose Start.TextContainer is not fixed/sequence content (second throw at line 449 is the container check).

Common situations: Passing a TextSelection from a FlowDocumentReader to a fixed-document annotation service; passing arbitrary objects (e.g. a TextPointer) as 'selection'; mixing flow and fixed anchoring processors.

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.EmptySelectionNotSupported
• Unsupported Selection
• anchorLocator.Parts
• annotation component
• Can only call SelectAll when CanSelectMultipleItems is true.

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/510dc454c67689c9. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Annotations/Anchoring/FixedTextSelectionProcessor.cs:449

            ITextPointer start = null;
            ITextRange textRange = selection as ITextRange;

            if (textRange != null)
            {
                start = textRange.Start;
                textSegments = textRange.TextSegments;
            }
            else
            {
                TextAnchor anchor = selection as TextAnchor;
                if (anchor != null)
                {
                    start = anchor.Start;
                    textSegments = anchor.TextSegments;
                }
                else
                {
                    throw new ArgumentException(SR.WrongSelectionType, $"selection: type={selection.GetType()}");
                }
            }

            if (!(start.TextContainer is FixedTextContainer ||
                start.TextContainer is DocumentSequenceTextContainer))
                throw new ArgumentException(SR.WrongSelectionType, $"selection: type={selection.GetType()}");

            return textSegments;
        }

        /// <summary>
        /// Checks if the selection object satisfies the requirements
        /// for this processor
        /// </summary>
        /// <param name="selection">selection</param>
        /// <returns>ITextRange interface, implemented by the object</returns>
        private TextAnchor CheckAnchor(object selection)
        {

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