dotnet/wpf · error · ArgumentException

Cannot compare different types.

Error message

Cannot compare different types.

What it means

CompoundFileStreamReference.CompareTo(object) only supports comparing against another CompoundFileStreamReference. Passing any other non-null object type throws ArgumentException (SR.CanNotCompareDiffTypes). The comparison itself is an ordinal compare of the upper-invariant full names.

Solutions

1. Keep stream references in a strongly typed List<CompoundFileStreamReference> before sorting.
2. Separate storages and streams into different collections and sort each independently.
3. Filter with OfType<CompoundFileStreamReference>() before any Sort/CompareTo.
4. If a cross-type ordering is needed, implement a custom comparer over a common property like FullName.

Example fix

// before
ArrayList refs = GetMixedReferences();
refs.Sort(); // ArgumentException on mixed types
// after
var streamRefs = GetMixedReferences().OfType<CompoundFileStreamReference>().ToList();
streamRefs.Sort();

if (other is CompoundFileStreamReference) { /* safe to compare */ }

bool IsComparableStreamRef(object o) => o is CompoundFileStreamReference;

try { result = streamRef.CompareTo(obj); }
catch (ArgumentException) { result = -1; /* or custom cross-type ordering */ }

When it happens

Trigger: Calling CompareTo on a CompoundFileStreamReference with a non-null argument of a different type — e.g. a CompoundFileStorageReference, a string, or an element of an object[]/ArrayList during Sort.

Common situations: Sorting heterogeneous reference collections in packaging utilities, mixing stream and storage references in one list, or accidentally boxing/typing arguments as object.

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.CanNotCompareDiffTypes
• ' ' ID is not a valid XSD ID.
• Cannot create a read-only stream.
• Cannot have leading path delimiter.
• CompoundFile path must be non-empty.

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/57ade77f6b95fe71. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/MS/Internal/IO/Packaging/CompoundFile/CompoundFileStreamReference.cs:106

        #endregion

        #region IComparable
        /// <summary>
        /// Compares two CompoundFileReferences
        /// </summary>
        /// <param name="o">CompoundFileReference to compare to this one</param>
        /// <remarks>Supports the IComparable interface</remarks>
        /// <returns>Less than zero if this instance is less than the given reference, zero if they are equal
        /// and greater than zero if this instance is greater than the given reference.  Not case sensitive.</returns>
        int IComparable.CompareTo(object o)
        {
            if (o == null)
                return 1;   // Standard behavior.

            // different type?
            if (o.GetType() != GetType())
                throw new ArgumentException(
                    SR.CanNotCompareDiffTypes);

            CompoundFileStreamReference r = (CompoundFileStreamReference)o;
            return String.CompareOrdinal(_fullName.ToUpperInvariant(), r._fullName.ToUpperInvariant());
        }
        #endregion

        //------------------------------------------------------
        //
        //   Private Methods
        //
        //------------------------------------------------------
        /// <summary>
        /// Initialize _fullName
        /// </summary>
        /// <remarks>this should only be called from constructors as references are immutable</remarks>
        /// <param name="fullName">string to parse</param>
        /// <exception cref="ArgumentException">if leading or trailing path delimiter</exception>

View on GitHub (pinned to 81131a70a4)