dotnet/wpf · error · InvalidOperationException

SR.Timing_NoTextChildren

Error message

SR.Timing_NoTextChildren

What it means

TimelineGroup.AddText always throws InvalidOperationException because timelines cannot accept text content. Text nodes appearing inside a timeline element in XAML (e.g. whitespace or stray text under <Storyboard>) have no representation and are rejected.

Solutions

  1. Remove any text content inside timeline elements in XAML
  2. Ensure only child element tags (animations/timelines) appear inside Storyboard/ParallelTimeline
  3. Check for invisible characters or malformed entity references inside the storyboard element

Example fix

// before
<Storyboard>
  Some stray text
  <DoubleAnimation .../>
</Storyboard>
// after
<Storyboard>
  <DoubleAnimation .../>
</Storyboard>
Defensive patterns

Strategy: validation

Validate before calling

if (!string.IsNullOrWhiteSpace(childText)) throw new ArgumentException("Timelines accept no text content");

Try / catch

try { storyboard.AddText(text); }
catch (InvalidOperationException) { /* remove text content from timeline */ }

Prevention

When it happens

Trigger: Calling AddText directly, or XAML parser encountering non-whitespace text content inside a Storyboard/ParallelTimeline element (often from stray characters or bad markup inside the storyboard).

Common situations: Accidental text/typo inside <Storyboard>...</Storyboard> in XAML; frameworks or tools generating XAML that inject text nodes into timeline containers.

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/14d134fa21624cbd. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/TimelineGroup.cs:203

        /// 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 Timeline'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 Timeline 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.Timing_NoTextChildren);
        }

        #endregion // IAddChild interface
    }
}

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