dotnet/wpf · error · InvalidOperationException

SR.Animation_NoTextChildren

Error message

SR.Animation_NoTextChildren

What it means

ObjectAnimationUsingKeyFrames.AddText always throws InvalidOperationException because key-frame timelines cannot accept text children. It is a generated IAddChild guard rejecting text content in timelines.

Solutions

  1. Remove text content from the animation element
  2. Provide values via ObjectKeyFrame children instead
  3. Trim/fix whitespace-producing XAML constructs like xml:space=preserve

Example fix

// before
<ObjectAnimationUsingKeyFrames>some text</ObjectAnimationUsingKeyFrames>
// after
<ObjectAnimationUsingKeyFrames><DiscreteObjectKeyFrame KeyTime="0:0:0" Value="someValue"/></ObjectAnimationUsingKeyFrames>
Defensive patterns

Strategy: validation

Validate before calling

if (content is string) throw new InvalidOperationException("Timelines do not accept text children");

Prevention

When it happens

Trigger: Calling AddText(string) directly, or XAML text/whitespace nodes inside <ObjectAnimationUsingKeyFrames>.

Common situations: XAML with stray text between elements, or code using IAddChild.AddText to set values.

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/c1a2c57dfe9a99f2. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/Generated/ObjectAnimationUsingKeyFrames.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 ObjectAnimationBase

        /// <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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