dotnet/wpf · error · ArgumentException

SR.Collection_BadType (GeneralTransform)

Error message

SR.Collection_BadType (GeneralTransform)

What it means

Thrown by the private Cast method (used by Add, Insert, and the collection constructor) when the value being added to a GeneralTransformCollection is not a GeneralTransform. The message names the collection type, the offending value's type, and the expected type 'GeneralTransform'.

Solutions

1. Only add objects deriving from GeneralTransform (e.g. TranslateTransform, RotateTransform, TransformGroup)
2. Check the object's runtime type with a type guard before Add/Insert
3. In XAML, verify child elements are transform types and namespaces are correct

Example fix

// before
collection.Add(myVisualBrush); // wrong type
// after
if (myVisualBrush is GeneralTransform t) { collection.Add(t); }

if (!(value is GeneralTransform)) throw new ArgumentException($"Expected GeneralTransform, got {value.GetType().Name}");

static bool IsGeneralTransform(object o) => o is GeneralTransform;

try { collection.Add(value); } catch (ArgumentException) { /* value is not a GeneralTransform — handle or log */ }

When it happens

Trigger: Calling collection.Add(someObject) or collection.Insert(i, someObject) where someObject is not derived from GeneralTransform — e.g. adding a string, a null-cast object, or a misconfigured XAML resource.

Common situations: XAML content mistakes (adding non-transform elements under <TransformGroup> or a GeneralTransformCollection resource), data binding producing the wrong type, or refactors where the wrong collection variable is used.

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.ScopeMustBeUIElementOrContent
• Can only countersign parts with Digital Signature…
• Duplicates not allowed - signature part already exists.
• ExtendedProperty is already part of the…
• GUID cannot be empty.

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/a2180af81d3a04b9. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Generated/GeneralTransformCollection.cs:506

                DependencyObject inheritanceChild = _collection[i];
                if (inheritanceChild != null && inheritanceChild.InheritanceContext == this)
                {
                    inheritanceChild.OnInheritanceContextChanged(args);
                }
            }
        }

        #endregion

        #region Private Helpers

        private GeneralTransform Cast(object value)
        {
            ArgumentNullException.ThrowIfNull(value);

            if (!(value is GeneralTransform))
            {
                throw new System.ArgumentException(SR.Format(SR.Collection_BadType, this.GetType().Name, value.GetType().Name, "GeneralTransform"));
            }

            return (GeneralTransform) value;
        }

        // IList.Add returns int and IList<T>.Add does not. This
        // is called by both Adds and IList<T>'s just ignores the
        // integer
        private int AddHelper(GeneralTransform value)
        {
            int index = AddWithoutFiringPublicEvents(value);

            // AddAtWithoutFiringPublicEvents incremented the version

            WritePostscript();

            return index;
        }

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