AvaloniaUI/Avalonia · error · ArgumentException

Key frame key is less than the previous one

Error message

Key frame key {key} is less than the previous one

What it means

Thrown by KeyFrames<T>.Validate when a newly inserted key frame has a lower normalizedProgressKey than the last (highest) key already in the collection. Key frames must be added in non-decreasing time order so the animation can interpolate forward.

Solutions

1. Insert key frames in ascending progress order.
2. Sort your frame data by progress key before inserting.
3. If you need a frame before the current last one, rebuild the animation from scratch in order.

Example fix

// before
anim.InsertKeyFrame(0.5f, mid);
anim.InsertKeyFrame(0.25f, early); // throws: 0.25 < 0.5
// after
anim.InsertKeyFrame(0.25f, early);
anim.InsertKeyFrame(0.5f, mid);

// ensure frames are in ascending key order before inserting
foreach (var f in frames.OrderBy(f => f.Key)) anim.InsertKeyFrame(f.Key, f.Value);

When it happens

Trigger: Inserting frames out of order, e.g. InsertKeyFrame(0.5f,...) followed by InsertKeyFrame(0.25f,...). The message includes the offending key value.

Common situations: Data-driven key frames sourced from an unsorted collection; inserting a 'starting' frame at 0 after already adding 0.5/1.0; loop that adds frames in reverse.

Related errors

• Key frame key
• Animation has no key frames
• Minimum allowed value is 1ms and maximum allowed value is…
• Animation Target can't be null
• Invalid animation duration

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/85b653a576bb9ee3. Report an issue: GitHub.

Appendix: source

Thrown at src/Avalonia.Base/Rendering/Composition/Animations/KeyFrames.cs:20

using System.Collections.Generic;
using Avalonia.Animation.Easings;
using Avalonia.Rendering.Composition.Expressions;

namespace Avalonia.Rendering.Composition.Animations
{
    
    /// <summary>
    /// Collection of composition animation key frames
    /// </summary>
    /// <typeparam name="T"></typeparam>
    class KeyFrames<T> : List<KeyFrame<T>>, IKeyFrames
    {
        void Validate(float key)
        {
            if (key < 0 || key > 1)
                throw new ArgumentException("Key frame key");
            if (Count > 0 && this[Count - 1].NormalizedProgressKey > key)
                throw new ArgumentException("Key frame key " + key + " is less than the previous one");
        }
        
        public void InsertExpressionKeyFrame(float normalizedProgressKey, string value, IEasing easingFunction)
        {
            Validate(normalizedProgressKey);
            Add(new KeyFrame<T>
            {
                NormalizedProgressKey = normalizedProgressKey,
                Expression = Expression.Parse(value),
                EasingFunction = easingFunction
            });
        }

        public void Insert(float normalizedProgressKey, T value, IEasing easingFunction)
        {
            Validate(normalizedProgressKey);
            Add(new KeyFrame<T>
            {

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