dotnet/wpf · error · ArgumentException

SR.IncorrectLocatorPartType

Error message

SR.IncorrectLocatorPartType ({locatorPart.PartType.Namespace}:{locatorPart.PartType.Name})

What it means

GetLocatorPartSegmentValues parses segment geometry out of a ContentLocatorPart. It first requires locatorPart.PartType to equal FixedTextElementName; any other part type throws ArgumentException(SR.IncorrectLocatorPartType) including the fully-qualified part type name. This protects against feeding e.g. a tree-selection locator part into the fixed processor.

Solutions

Create locator parts with FixedTextSelectionProcessor.CreateLocatorPart / matching PartType.
Check locatorPart.PartType == FixedTextSelectionProcessor.FixedTextElementName before resolving.
Route each locator through the processor whose Id/PartType matches.

Example fix

// before
var part = new ContentLocatorPart(treeSelectionProcessorPartType);
fixedProcessor.ResolveLocatorPart(part, docPage, out level);
// after
var part = new ContentLocatorPart(FixedTextSelectionProcessor.FixedTextElementName);
part.NameValuePairs["Count"] = "1";
fixedProcessor.ResolveLocatorPart(part, docPage, out level);

Defensive patterns

Strategy: validation

Validate before calling

if (locatorPart.PartType != FixedTextSelectionProcessor.FixedTextElementName) throw new InvalidOperationException($"Unexpected PartType {locatorPart.PartType.Name}");

Try / catch

try { processor.ResolveLocatorPart(part, node, out var level); } catch (ArgumentException ex) { /* wrong processor for this part type */ }

Prevention

Route each ContentLocatorPart to the processor that created it
Check PartType before resolution
Avoid cross-loading annotation stores from foreign apps

When it happens

Trigger: Calling ResolveLocatorPart (which calls GetLocatorPartSegmentValues) with a ContentLocatorPart whose PartType differs from the FixedText element name — e.g. a ContentLocatorPart created for the tree selection processor.

Common situations: Cross-wiring processors: annotations created under a TreeSelectionProcessor resolved through the fixed processor; manually built locator parts with wrong PartType; loading annotation stores written by other applications.

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

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/647c309215290588. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/Annotations/Anchoring/FixedTextSelectionProcessor.cs:493

                throw new ArgumentException(SR.WrongSelectionType, $"selection: type={selection.GetType()}");
            }

            return anchor;
        }

        /// <summary>
        ///     Extracts the values of attributes from a locator part.
        /// </summary>
        /// <param name="locatorPart">the locator part to extract values from</param>
        /// <param name="segmentNumber">number of segment value to retrieve</param>
        /// <param name="start">the start point value based on StartXAttribute and StartYAttribute values</param>
        /// <param name="end">the end point value based on EndXAttribyte and EndYattribute values</param>
        private void GetLocatorPartSegmentValues(ContentLocatorPart locatorPart, int segmentNumber, out Point start, out Point end)
        {
            ArgumentNullException.ThrowIfNull(locatorPart);

            if (FixedTextElementName != locatorPart.PartType)
                throw new ArgumentException(SR.Format(SR.IncorrectLocatorPartType, $"{locatorPart.PartType.Namespace}:{locatorPart.PartType.Name}"), nameof(locatorPart));

            string segmentValue = locatorPart.NameValuePairs[TextSelectionProcessor.SegmentAttribute + segmentNumber.ToString(NumberFormatInfo.InvariantInfo)];
            if (segmentValue == null)
                throw new ArgumentException(SR.Format(SR.InvalidLocatorPart, TextSelectionProcessor.SegmentAttribute + segmentNumber.ToString(NumberFormatInfo.InvariantInfo)));

            ReadOnlySpan<char> segmentValueSpan = segmentValue.AsSpan();
            Span<Range> splitRegions = stackalloc Range[5];

            if (segmentValueSpan.Split(splitRegions, TextSelectionProcessor.Separator) != 4)
                throw new ArgumentException(SR.Format(SR.InvalidLocatorPart, TextSelectionProcessor.SegmentAttribute + segmentNumber.ToString(NumberFormatInfo.InvariantInfo)));

            start = GetPoint(segmentValueSpan[splitRegions[0]], segmentValueSpan[splitRegions[1]]);
            end = GetPoint(segmentValueSpan[splitRegions[2]], segmentValueSpan[splitRegions[3]]);
        }

        /// <summary>
        /// Calculates <see cref="Point"/> out of X and Y values supplied as a <see cref="string"/>.
        /// </summary>

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