dotnet/wpf · error · ArgumentException

ExtendedProperty is already part of the…

Error message

ExtendedProperty is already part of the ExtendedPropertyCollection.

What it means

ExtendedPropertyCollection.Add(Guid, object) first checks Contains(id) and throws ArgumentException(SR.EPExists, nameof(id)) — 'ExtendedProperty is already part of the ExtendedPropertyCollection.' — when a property with the same GUID already exists. The collection requires unique keys; duplicates must go through the indexer's set accessor instead.

Solutions

1. Use the indexer (collection[guid] = value) to overwrite an existing property instead of Add.
2. Check Contains(guid) before Add and skip, overwrite, or remove-then-add as appropriate.
3. Deduplicate property lists before decoding/persisting ISF so the same id isn't added twice.
4. Catch ArgumentException with the 'id' param name to handle duplicates from external data gracefully.

Example fix

// before
properties.Add(guid, value); // ArgumentException if guid already present
// after
if (properties.Contains(guid))
    properties[guid] = value;
else
    properties.Add(guid, value);

if (properties.Contains(id))
    properties[id] = value;
else
    properties.Add(id, value);

static bool IsNewProperty(ExtendedPropertyCollection c, Guid id) => !c.Contains(id);

try { properties.Add(id, value); }
catch (ArgumentException ex) when (ex.ParamName == "id") { properties[id] = value; /* upsert */ }

When it happens

Trigger: Calling Add(guid, value) twice with the same GUID; decoding ISF (DecodeRawISF) whose payload lists the same property id more than once for one object.

Common situations: Applying default properties on ink objects that already have them; replaying/importing ISF data with duplicated property tags (double-applied transforms or merges); re-running an import routine without clearing the collection.

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

• Property not set.
• The GUID is not part of the ExtendedPropertyCollection.
• GUID cannot be empty.
• InvalidMatrixContainsInfinity
• InvalidMatrixContainsNaN

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/7f1972c368fb604c. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/MS/internal/Ink/ExtendedPropertyCollection.cs:150

        {
            ExtendedPropertyCollection copied = new ExtendedPropertyCollection();
            for (int x = 0; x < _extendedProperties.Count; x++)
            {
                copied.Add(_extendedProperties[x].Clone());
            }
            return copied;
        }

        /// <summary>
        /// Add
        /// </summary>
        /// <param name="id">Id</param>
        /// <param name="value">value</param>
        internal void Add(Guid id, object value)
        {
            if (this.Contains(id))
            {
                throw new ArgumentException(SR.EPExists, nameof(id));
            }

            ExtendedProperty extendedProperty = new ExtendedProperty(id, value);

            //this will raise change events
            this.Add(extendedProperty);
        }


        /// <summary>
        /// Remove
        /// </summary>
        /// <param name="id">id</param>
        internal void Remove(Guid id)
        {
            if (!Contains(id))
            {
                throw new ArgumentException(SR.EPGuidNotFound, nameof(id));

View on GitHub (pinned to 81131a70a4)