dotnet/wpf · error · InvalidOperationException

SR.Animation_NoTextChildren

Error message

SR.Animation_NoTextChildren

What it means

DecimalAnimationUsingKeyFrames.AddText always throws InvalidOperationException (SR.Animation_NoTextChildren). Timelines do not support text children; this virtual is deliberately implemented as a throw and the XML docs note it.

Solutions

  1. Remove any text inside the DecimalAnimationUsingKeyFrames element in XAML
  2. Express values as key frame child elements
  3. Use KeyFrames.Add programmatically instead of AddText
  4. Scan the XAML for accidental literal values between tags

Example fix

// before (XAML)
<DecimalAnimationUsingKeyFrames>50</DecimalAnimationUsingKeyFrames>
// after (XAML)
<DecimalAnimationUsingKeyFrames>
  <LinearDecimalKeyFrame KeyTime="0:0:1" Value="50" />
</DecimalAnimationUsingKeyFrames>
Defensive patterns

Strategy: validation

Validate before calling

// validate before parse/insert: reject non-whitespace text nodes under the animation element

Try / catch

try { addText(childText); }
catch (InvalidOperationException) { /* use a key frame child instead */ }

Prevention

When it happens

Trigger: Calling AddText(string) directly, or XAML parsing when literal text (including stray non-whitespace characters) appears inside a <DecimalAnimationUsingKeyFrames> element.

Common situations: Typos or stray characters in XAML inside the animation element; code treating the animation as a text content container.

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/47ebe1a9c416d79d. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/Generated/DecimalAnimationUsingKeyFrames.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 DecimalAnimationBase

        /// <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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