{"record":{"id":"7728a4a501e8dda4","repo":"dotnet/wpf","slug":"sr-typemetadataalreadyinuse","errorCode":null,"errorMessage":"SR.TypeMetadataAlreadyInUse","messagePattern":"SR\\.TypeMetadataAlreadyInUse","errorType":"exception","errorClass":"ArgumentException","httpStatus":null,"severity":"error","filePath":"src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/DependencyProperty.cs","lineNumber":455,"sourceCode":"\n\n        /// <summary>\n        ///     Parameter validation for OverrideMetadata, includes code to force\n        /// all base classes of \"forType\" to register their metadata so we know\n        /// what we are overriding.\n        /// </summary>\n        private void SetupOverrideMetadata(\n                Type forType,\n                PropertyMetadata typeMetadata,\n            out DependencyObjectType dType,\n            out PropertyMetadata baseMetadata )\n        {\n            ArgumentNullException.ThrowIfNull(forType);\n            ArgumentNullException.ThrowIfNull(typeMetadata);\n\n            if (typeMetadata.Sealed)\n            {\n                throw new ArgumentException(SR.TypeMetadataAlreadyInUse);\n            }\n\n            if (!typeof(DependencyObject).IsAssignableFrom(forType))\n            {\n                throw new ArgumentException(SR.Format(SR.TypeMustBeDependencyObjectDerived, forType.Name));\n            }\n\n            // Ensure default value is a correct value (if it was supplied,\n            // otherwise, the default value will be taken from the base metadata\n            // which was already validated)\n            if (typeMetadata.IsDefaultValueModified)\n            {\n                // Will throw ArgumentException if fails.\n                ValidateMetadataDefaultValue( typeMetadata, PropertyType, Name, ValidateValueCallback );\n            }\n\n            // Force all base classes to register their metadata\n            dType = DependencyObjectType.FromSystemType(forType);","sourceCodeStart":437,"sourceCodeEnd":473,"githubUrl":"https://github.com/dotnet/wpf/blob/81131a70a4c573cd62748a5c36908fc4d662daa9/src/Microsoft.DotNet.Wpf/src/WindowsBase/System/Windows/DependencyProperty.cs#L437-L473","documentation":"OverrideMetadata rejects a typeMetadata instance that has already been sealed. Metadata becomes sealed when first used (registered or overridden); reusing the same PropertyMetadata object for a second OverrideMetadata call is not allowed because the property system mutates and freezes it.","triggerScenarios":"Sharing one PropertyMetadata instance across two OverrideMetadata calls, or calling OverrideMetadata with the same metadata that was passed to Register.","commonSituations":"Static readonly shared metadata fields reused for several properties/types; refactoring that hoists a metadata literal into a shared variable.","solutions":["Create a new PropertyMetadata (or derived) instance for each OverrideMetadata call.","If defaults must be shared, share the default value object, not the metadata instance.","Call OverrideMetadata only once per (property, forType) pair."],"exampleFix":"// before\nprivate static readonly PropertyMetadata SharedMeta = new PropertyMetadata(5);\nA.OverrideMetadata(WidthProperty, SharedMeta);\nB.OverrideMetadata(WidthProperty, SharedMeta); // throws\n// after\nA.OverrideMetadata(WidthProperty, new PropertyMetadata(5));\nB.OverrideMetadata(WidthProperty, new PropertyMetadata(5));","handlingStrategy":"validation","validationCode":"if (metadata.Sealed) throw new InvalidOperationException(\"Metadata instance already sealed; create a new one\");","typeGuard":"static bool IsReusableMetadata(PropertyMetadata m) => !m.Sealed;","tryCatchPattern":null,"preventionTips":["Never share PropertyMetadata instances across Register/OverrideMetadata calls","Share default value objects instead of metadata objects"],"tags":["wpf","dependency-property","metadata"],"backgroundTag":"invalid-state-transition","analyzedSha":"81131a70a4c573cd62748a5c36908fc4d662daa9","analyzedAt":"2026-09-14T10:12:48.479Z","contentChangedAt":"2026-09-14T10:12:48.479Z","schemaVersion":2},"datasetVersion":"2026-09-21T21:30:21.729Z"}