dotnet/wpf · error · InvalidOperationException

SR.Timing_RepeatBehaviorNotIterationCount

Error message

SR.Timing_RepeatBehaviorNotIterationCount

What it means

RepeatBehavior.Count returns the iteration count only when the instance represents one (HasCount / KeyTimeType-style IterationCount). Reading Count on a RepeatBehavior created as Forever, a RepeatBehavior(TimeSpan), or the default throws InvalidOperationException with Timing_RepeatBehaviorNotIterationCount.

Solutions

  1. Guard with if (rb.HasCount) before accessing rb.Count.
  2. Branch on the behavior: HasCount -> Count, HasDuration -> Duration, Forever -> infinite handling.
  3. Do not treat Count as a numeric fallback; use HasCount/HasDuration to pick the property.

Example fix

// before
double count = repeatBehavior.Count;
// after
double count = repeatBehavior.HasCount ? repeatBehavior.Count : 0;
Defensive patterns

Strategy: type-guard

Validate before calling

double? count = repeatBehavior.HasCount ? repeatBehavior.Count : (double?)null;

Type guard

static bool HasIterationCount(RepeatBehavior rb) => rb.HasCount;
static double? SafeCount(RepeatBehavior rb) => rb.HasCount ? rb.Count : (double?)null;

Try / catch

double count;
try { count = repeatBehavior.Count; }
catch (InvalidOperationException) { count = 0; }

Prevention

When it happens

Trigger: Reading rb.Count when rb was built with new RepeatBehavior(TimeSpan.FromSeconds(2)), is RepeatBehavior.Forever, or is default(RepeatBehavior). Example: double n = RepeatBehavior.Forever.Count; throws.

Common situations: Serializing animation settings without checking the behavior type; UI code that assumes every RepeatBehavior has a count; migrating code that used an older API where count was always set.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/bc25d2c07f98cad4. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/RepeatBehavior.cs:110

        public bool HasDuration
        {
            get
            {
                return _type == RepeatBehaviorType.RepeatDuration;
            }
        }

        /// <summary>
        /// Returns the iteration count specified by this RepeatBehavior.
        /// </summary>
        /// <value>The iteration count specified by this RepeatBehavior.</value>
        /// <exception cref="InvalidOperationException">Thrown if this RepeatBehavior does not represent an iteration count.</exception>
        public double Count
        {
            get
            {
                if (!HasCount)
                    throw new InvalidOperationException(SR.Format(SR.Timing_RepeatBehaviorNotIterationCount, this));

                return _iterationCount;
            }
        }

        /// <summary>
        /// Returns the repeat duration specified by this RepeatBehavior.
        /// </summary>
        /// <value>A TimeSpan representing the repeat duration specified by this RepeatBehavior.</value>
        /// <exception cref="InvalidOperationException">Thrown if this RepeatBehavior does not represent a repeat duration.</exception>
        public TimeSpan Duration
        {
            get
            {
                if (!HasDuration)
                    throw new InvalidOperationException(SR.Format(SR.Timing_RepeatBehaviorNotRepeatDuration, this));

                return _repeatDuration;

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