dotnet/wpf · error · InvalidOperationException

SR.Animation_NoTextChildren

Error message

SR.Animation_NoTextChildren

What it means

CharAnimationUsingKeyFrames.AddText unconditionally throws InvalidOperationException (SR.Animation_NoTextChildren) because key-frame timelines cannot accept text as content. The override exists only to satisfy the IAddChild contract and always fails.

Solutions

  1. Remove all inner text from the <CharAnimationUsingKeyFrames> element
  2. Specify values using key-frame child elements such as <DiscreteCharKeyFrame Value="a" .../>
  3. In code, populate animation.KeyFrames instead of calling AddText

Example fix

// before (XAML)
<CharAnimationUsingKeyFrames>abc</CharAnimationUsingKeyFrames>
// after
<CharAnimationUsingKeyFrames>
  <DiscreteCharKeyFrame Value="a" KeyTime="0:0:0"/>
  <DiscreteCharKeyFrame Value="c" KeyTime="0:0:1"/>
</CharAnimationUsingKeyFrames>
Defensive patterns

Strategy: validation

Validate before calling

// XAML guard: element body must contain no text nodes — only key-frame child elements

Try / catch

try { adder.AddText(text); }
catch (InvalidOperationException) { /* timelines take no text: use key-frame children */ }

Prevention

When it happens

Trigger: Literal text placed inside <CharAnimationUsingKeyFrames> tags in XAML, or a direct programmatic call to AddText.

Common situations: Stray text or whitespace characters inside the XAML animation element; attempts to specify char values as inner text.

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/470e392a8207d67c. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/Generated/CharAnimationUsingKeyFrames.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 CharAnimationBase

        /// <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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