dotnet/wpf · error · InvalidOperationException

SR.Animation_NoTextChildren

Error message

SR.Animation_NoTextChildren

What it means

MatrixAnimationUsingKeyFrames.AddText always throws InvalidOperationException because key-frame timelines cannot accept text children. This is an intentional guard generated for all timeline classes to reject unsupported XAML content via IAddChild.

Solutions

  1. Remove the text child from the animation element or call site; key-frame animations accept only KeyFrame children via AddChild
  2. If configuring animation values, use KeyFrames collection or the animated property path instead of text
  3. Check for XML whitespace/text nodes inside the element in XAML

Example fix

// before
anim.AddText("0,0");
// after
anim.KeyFrames.Add(new DiscreteMatrixKeyFrame(Matrix.Identity, KeyTime.FromTimeSpan(TimeSpan.FromSeconds(1))));
Defensive patterns

Strategy: validation

Validate before calling

if (xamlNode.NodeType == XamlNodeType.Value && xamlNode.Value is string) throw new InvalidOperationException("Timelines do not accept text children");

Prevention

When it happens

Trigger: Calling AddText(string) directly, or XAML parsing that places a text run inside a <MatrixAnimationUsingKeyFrames> element.

Common situations: Hand-editing XAML with whitespace/text nodes or stray characters inside the animation element; programmatic IAddChild-based construction of timelines.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/d1b79e06a28bae71. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/Generated/MatrixAnimationUsingKeyFrames.cs:277

        /// WritePreamble() or WritePostscript().  It also doesn't throw an
        /// ArgumentNullException if the childText parameter is null.  These tasks
        /// are performed by the interface implementation.  Therefore, it's OK
        /// for a derived class to override this method and call the base
        /// class implementation only if they determine that it's the right
        /// course of action.  The derived class can rely on KeyFrameAnimation's
        /// implementation of IAddChild.AddChild or implement their own
        /// following the Freezable pattern since that would be a public
        /// method.
        /// </remarks>
        /// <param name="childText">A string representing the child text that
        /// should be added.  If this is a KeyFrameAnimation an exception will be
        /// thrown.</param>
        /// <exception cref="InvalidOperationException">Timelines have no way
        /// of adding text.</exception>
        [EditorBrowsable(EditorBrowsableState.Advanced)]
        protected virtual void AddText(string childText)
        {
            throw new InvalidOperationException(SR.Animation_NoTextChildren);
        }

        #endregion

        #region MatrixAnimationBase

        /// <summary>
        /// Calculates the value this animation believes should be the current value for the property.
        /// </summary>
        /// <param name="defaultOriginValue">
        /// This value is the suggested origin value provided to the animation
        /// to be used if the animation does not have its own concept of a
        /// start value. If this animation is the first in a composition chain
        /// this value will be the snapshot value if one is available or the
        /// base property value if it is not; otherise this value will be the 
        /// value returned by the previous animation in the chain with an 
        /// animationClock that is not Stopped.
        /// </param>

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