{"record":{"id":"f3c375d99d3ed270","repo":"stride3d/stride","slug":"cannot-instantiate-an-object-for-type-objectcontext","errorCode":null,"errorMessage":"Cannot instantiate an object for type [{objectContext.Descriptor}]","messagePattern":"Cannot instantiate an object for type \\[(.+?)\\]","errorType":"exception","errorClass":"YamlException","httpStatus":null,"severity":"error","filePath":"sources/core/Stride.Core.Yaml/Serialization/Serializers/ObjectSerializer.cs","lineNumber":174,"sourceCode":"\n        /// <summary>\n        /// Reads the members from the current stream.\n        /// </summary>\n        /// <typeparam name=\"TStart\">The type of the t start.</typeparam>\n        /// <typeparam name=\"TEnd\">The type of the t end.</typeparam>\n        /// <param name=\"objectContext\"></param>\n        /// <returns>Return the object being read, by default thisObject passed by argument.</returns>\n        protected virtual void ReadMembers<TStart, TEnd>(ref ObjectContext objectContext)\n            where TStart : NodeEvent\n            where TEnd : ParsingEvent\n        {\n            var reader = objectContext.Reader;\n            var start = reader.Expect<TStart>();\n\n            // throws an exception while deserializing\n            if (objectContext.Instance == null)\n            {\n                throw new YamlException(start.Start, start.End, $\"Cannot instantiate an object for type [{objectContext.Descriptor}]\");\n            }\n\n            while (!reader.Accept<TEnd>())\n            {\n                ReadMember(ref objectContext);\n            }\n            reader.Expect<TEnd>();\n        }\n\n        /// <summary>\n        /// Reads an item of the object from the YAML flow (either a sequence item or mapping key/value item).\n        /// </summary>\n        /// <param name=\"objectContext\"></param>\n        /// <exception cref=\"YamlException\">Unable to deserialize property [{0}] not found in type [{1}].DoFormat(propertyName, typeDescriptor)</exception>\n        protected virtual void ReadMember(ref ObjectContext objectContext)\n        {\n            Scalar memberScalar;\n            string memberName;","sourceCodeStart":156,"sourceCodeEnd":192,"githubUrl":"https://github.com/stride3d/stride/blob/96fad776d210c221682aac1ccdf4c79dc046fc38/sources/core/Stride.Core.Yaml/Serialization/Serializers/ObjectSerializer.cs#L156-L192","documentation":"ObjectSerializer.ReadMembers expects the object instance to have been created before reading its members. If objectContext.Instance is still null after the instantiation step, a YamlException with the node's span is thrown — the library could not construct an object of the target type.","triggerScenarios":"Deserializing a mapping node whose target type cannot be instantiated: abstract type without a registered concrete mapping, type with no usable constructor, constructor throwing, or null produced by a custom ObjectFactory.","commonSituations":"Polymorphic YAML lacking the concrete type discriminator; constructor signature changed after refactor/upgrade; serializer for interface-typed members without realignment; activation errors in AOT/trimming environments.","solutions":["Check for a prior exception/activation failure — the constructor or ObjectFactory likely threw or returned null","Register realignment (abstract type -> concrete type) so the concrete type can be instantiated","Ensure the type has an accessible parameterless or matching constructor","Verify the YAML contains the concrete type tag when serializing polymorphic members"],"exampleFix":"// before\n// property typed IFoo serialized as plain mapping, no concrete type\nmyFoo:\n  Bar: 1\n// after\nmyFoo:\n  Bar: 1\n  ~ConcreteFoo: {}   // or ensure type tag / realignment is emitted","handlingStrategy":"validation","validationCode":"if (targetType.IsAbstract || targetType.IsInterface)\n    serializerContext.Services?.GetService<RealOffset>();\n// ensure realignment registered:\nif (!factory.CanInstantiate(targetType))\n    throw new InvalidOperationException($\"Register a concrete type for {targetType}\");","typeGuard":"static bool CanActivate(Type t) => !t.IsAbstract && !t.IsInterface && t.GetConstructor(Type.EmptyTypes) != null;","tryCatchPattern":"try\n{\n    objectSerializer.ReadYaml(ref objectContext);\n}\ncatch (YamlException ex) when (ex.Message.Contains(\"Cannot instantiate an object for type\"))\n{\n    // register realignment or supply an ObjectFactory, then retry\n}","preventionTips":["Keep parameterless constructors on serialized types","Register realignment for interface/abstract member types","Ensure polymorphic YAML always carries the concrete type tag","Watch for constructor exceptions logged before this error"],"tags":["yaml","deserialization","instantiation"],"backgroundTag":"json-unmarshal-failed","analyzedSha":"96fad776d210c221682aac1ccdf4c79dc046fc38","analyzedAt":"2026-09-14T02:59:31.279Z","contentChangedAt":"2026-09-14T02:59:31.279Z","schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}