{"record":{"id":"9ed3851f1ab35720","repo":"dotnet/wpf","slug":"sr-animation-childmustbekeyframe","errorCode":null,"errorMessage":"SR.Animation_ChildMustBeKeyFrame","messagePattern":"SR\\.Animation_ChildMustBeKeyFrame","errorType":"exception","errorClass":"ArgumentException","httpStatus":null,"severity":"error","filePath":"src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/Generated/CharAnimationUsingKeyFrames.cs","lineNumber":227,"sourceCode":"            WritePostscript();\n        }\n\n        /// <summary>\n        /// Implemented to allow KeyFrames to be direct children\n        /// of KeyFrameAnimations in markup.\n        /// </summary>\n        [EditorBrowsable(EditorBrowsableState.Advanced)]\n        protected virtual void AddChild(object child)\n        {\n            CharKeyFrame keyFrame = child as CharKeyFrame;\n\n            if (keyFrame != null)\n            {\n                KeyFrames.Add(keyFrame);\n            }\n            else\n            {        \n                throw new ArgumentException(SR.Animation_ChildMustBeKeyFrame, nameof(child));\n            }\n        }\n\n        /// <summary>\n        /// Adds a text string as a child of this KeyFrameAnimation.\n        /// </summary>\n        /// <param name=\"childText\">\n        /// The text to add.\n        /// </param>\n        /// <remarks>\n        /// A KeyFrameAnimation does not accept text as a child, so this method will\n        /// raise an InvalididOperationException unless a derived class has\n        /// overridden the behavior to add text.\n        /// </remarks>\n        /// <exception cref=\"ArgumentNullException\">The childText parameter is\n        /// null.</exception>\n        void IAddChild.AddText(string childText)\n        {","sourceCodeStart":209,"sourceCodeEnd":245,"githubUrl":"https://github.com/dotnet/wpf/blob/81131a70a4c573cd62748a5c36908fc4d662daa9/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/Generated/CharAnimationUsingKeyFrames.cs#L209-L245","documentation":"CharAnimationUsingKeyFrames.AddChild throws ArgumentException (SR.Animation_ChildMustBeKeyFrame, paramName \"child\") when the child added through IAddChild is null or not a CharKeyFrame. Only char-typed key frames may be children of this key-frame animation.","triggerScenarios":"XAML IAddChild usage with a non-CharKeyFrame child inside <CharAnimationUsingKeyFrames>, or calling AddChild(null)/AddChild(wrongType).","commonSituations":"XAML authoring mistakes: wrong key-frame type (e.g. ByteKeyFrame inside a char animation) or nested plain values instead of key frames.","solutions":["Add only CharKeyFrame children, e.g. <DiscreteCharKeyFrame Value=\"a\" KeyTime=\"0:0:1\"/>","Use animation.KeyFrames.Add(new DiscreteCharKeyFrame(...)) in code","Use a different animation type if plain values were intended"],"exampleFix":"// before (XAML)\n<CharAnimationUsingKeyFrames>\n  <String>a</String>\n</CharAnimationUsingKeyFrames>\n// after\n<CharAnimationUsingKeyFrames>\n  <DiscreteCharKeyFrame Value=\"a\" KeyTime=\"0:0:1\"/>\n</CharAnimationUsingKeyFrames>","handlingStrategy":"validation","validationCode":"if (child is CharKeyFrame kf) animation.KeyFrames.Add(kf);\nelse throw new ArgumentException(\"Child must be a CharKeyFrame\", nameof(child));","typeGuard":"static bool IsKeyFrameChild(object o) => o is CharKeyFrame;","tryCatchPattern":"try { adder.AddChild(child); }\ncatch (ArgumentException ex) when (ex.ParamName == \"child\") { /* child was not a CharKeyFrame; fix the child element type */ }","preventionTips":["In XAML, nest only CharKeyFrame-derived elements inside CharAnimationUsingKeyFrames","Match key-frame value type to the animation's char value type","Prefer the KeyFrames collection property in code over IAddChild"],"tags":["wpf","animation","xaml","keyframe","invalid-child"],"backgroundTag":"invalid-argument-value","analyzedSha":"81131a70a4c573cd62748a5c36908fc4d662daa9","analyzedAt":"2026-09-14T10:12:48.479Z","contentChangedAt":"2026-09-14T10:12:48.479Z","schemaVersion":2},"datasetVersion":"2026-09-22T01:17:13.364Z"}