dotnet/wpf · error · ArgumentException

SR.Collection_BadDestArray

Error message

SR.Collection_BadDestArray

What it means

This SR resource backs an ArgumentException (wrapping an InvalidCastException) thrown by the generated ICollection.CopyTo(Array, int) implementation (CollectionHelper.cs, Collection_SetValue) when a collection element cannot be stored in the destination array's element type. The message includes the collection type name to aid diagnosis.

Solutions

  1. Allocate the destination array with the collection's element type (or a compatible base type)
  2. Validate array element-type compatibility before calling CopyTo
  3. Use CopyTo(T[], int) or enumeration instead of the Array overload when types differ
  4. Catch ArgumentException and surface the collection type name to diagnose the mismatch

Example fix

// before
var dest = new int[collection.Count];
collection.CopyTo(dest, 0); // BadDestArray
// after
var dest = new MyElementType[collection.Count];
collection.CopyTo(dest, 0);
Defensive patterns

Strategy: validation

Validate before calling

var elemType = array.GetType().GetElementType();
if (elemType == null || !typeof(MyElementType).IsAssignableFrom(elemType))
    throw new ArgumentException("array element type incompatible");

Try / catch

try { collection.CopyTo(array, index); }
catch (ArgumentException) { copyViaEnumeration(collection, array, index); }

Prevention

When it happens

Trigger: Calling CopyTo with a destination array whose element type is not assignable from the collection's element type (e.g. copying a typed collection into an incompatible array), causing Array.SetValue to throw InvalidCastException which is wrapped.

Common situations: Passing narrowly typed arrays through object[]-typed code paths; covariance assumptions between similar element types; refactoring element types so old call sites' arrays no longer match.

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

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/9a20f250297007b4. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WpfGfx/codegen/mcg/helpers/CollectionHelper.cs:384

                        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);
                        }
                    }
                [[/inline]];

        }

        public static string WriteCopyToCommon(McgResource resource)
        {
            return
                [[inline]]
                    ReadPreamble();

                    ArgumentNullException.ThrowIfNull(array);

                    // This will not throw in the case that we are copying
                    // from an empty collection.  This is consistent with the
                    // BCL Collection implementations. (Windows 1587365)
                    ArgumentOutOfRangeException.ThrowIfNegative(index);

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