dotnet/wpf · error · ArgumentException

SR.Collection_BadDestArray

Error message

SR.Collection_BadDestArray

What it means

CopyTo wraps InvalidCastException and rethrows ArgumentException (SR.Collection_BadDestArray) when an element cannot be stored into the destination array, i.e. the array's element type is not assignment-compatible with Transform3D.

Solutions

  1. Use an array whose element type is Transform3D (or object), or use the generic CopyTo(Transform3D[], int) overload.
  2. Prefer iterating with foreach into a correctly typed buffer.
  3. Verify the array element type with typeof(Transform3D).IsAssignableFrom(arr.GetType().GetElementType()) before calling.

Example fix

// before
var target = new Visual3D[collection.Count];
((ICollection)collection).CopyTo(target, 0);
// after
var target = new Transform3D[collection.Count];
collection.CopyTo(target, 0);
Defensive patterns

Strategy: validation

Validate before calling

var elemType = array.GetType().GetElementType();
if (!typeof(Transform3D).IsAssignableFrom(elemType) && elemType != typeof(object))
    throw new ArgumentException("Bad destination array type");

Type guard

bool IsCompatible(Array a) => a != null && (a.GetType().GetElementType() == typeof(Transform3D) || a.GetType().GetElementType() == typeof(object));

Try / catch

try { ((ICollection)collection).CopyTo(arr, 0); } catch (ArgumentException e) when (e.InnerException is InvalidCastException) { /* reallocate correctly-typed array */ }

Prevention

When it happens

Trigger: Calling the non-generic ICollection.CopyTo with an array whose element type cannot hold Transform3D (e.g. new Visual3D[3] or new object[3] only works via boxing, but an unrelated type like new string[3] fails), causing SetValue to throw InvalidCastException.

Common situations: Legacy ICollection-based code passing arrays typed for another collection's element type; refactoring element types between Visual3D/Transform3D collections; reflection-driven copy utilities.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/31e3ef59a98352bb. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media3D/Generated/Transform3DCollection.cs:427

            if (array.Rank != 1)
            {
                throw new ArgumentException(SR.Collection_BadRank);
            }

            // Elsewhere in the collection we throw an AE when the type is
            // bad so we do it here as well to be consistent
            try
            {
                int count = _collection.Count;
                for (int i = 0; i < count; i++)
                {
                    array.SetValue(_collection[i], index + i);
                }
            }
            catch (InvalidCastException e)
            {
                throw new ArgumentException(SR.Format(SR.Collection_BadDestArray, this.GetType().Name), e);
            }
        }

        bool ICollection.IsSynchronized
        {
            get
            {
                ReadPreamble();

                return IsFrozen || Dispatcher != null;
            }
        }

        object ICollection.SyncRoot
        {
            get
            {
                ReadPreamble();

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