dotnet/wpf · error · ArgumentNullException

Int32KeyFrameCollection

Error message

Int32KeyFrameCollection[{0}]

What it means

The Int32KeyFrameCollection indexer setter throws ArgumentNullException whose message is the formatted string 'Int32KeyFrameCollection[{index}]' when a null key frame is assigned at an index. Null key frames are not permitted in the collection.

Solutions

1. Check the key frame for null before assigning into the collection.
2. Only add Int32KeyFrame instances that were successfully constructed.
3. Log/validate the source of the null frame upstream.

Example fix

// before
keyFrames[0] = GetFrame(); // may return null
// after
var frame = GetFrame();
if (frame != null) keyFrames[0] = frame;

if (frame == null)
    throw new InvalidOperationException($"No key frame available for index {index}; refusing to insert null into Int32KeyFrameCollection.");

bool IsValidFrame(Int32KeyFrame f) => f != null;

try { keyFrames[index] = frame; }
catch (ArgumentNullException ex) when (ex.Message.Contains("Int32KeyFrameCollection[")) {
    // substitute a valid default key frame or log and skip
}

When it happens

Trigger: Executing keyFrames[index] = null; on an Int32KeyFrameCollection.

Common situations: Programmatic construction of key-frame collections where a frame variable is unexpectedly null; deserialization or data-binding producing null frames.

Related errors

• Int64KeyFrameCollection
• PointKeyFrameCollection
• RectKeyFrameCollection
• ColorKeyFrameCollection
• DecimalKeyFrameCollection

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/a317b085c206897e. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/Generated/Int32KeyFrameCollection.cs:466

            }
        }

        /// <summary>
        /// Gets or sets the Int32KeyFrame at a given index.
        /// </summary>
        public Int32KeyFrame this[int index]
        {
            get
            {
                ReadPreamble();

                return _keyFrames[index];
            }
            set
            {
                if (value == null)
                {
                    throw new ArgumentNullException(String.Format(CultureInfo.InvariantCulture, "Int32KeyFrameCollection[{0}]", index));
                }

                WritePreamble();

                if (value != _keyFrames[index])
                {
                    OnFreezablePropertyChanged(_keyFrames[index], value);
                    _keyFrames[index] = value;

                    Debug.Assert(_keyFrames[index] != null);

                    WritePostscript();
                }
            }
        }

        #endregion
    }

View on GitHub (pinned to 81131a70a4)