Avalonia中的动画

public class StringAnimator : InterpolatingAnimator<string>
{
    /// <summary>
    /// 计算插值结果。
    /// </summary>
    /// <param name="progress">进度：0到1之间的值，指在两个关键帧之间过渡的时间位置。</param>
    /// <param name="oldValue">旧值：动画开始时，第一个关键帧的值。</param>
    /// <param name="newValue">新值：动画结束时，最后一个关键帧的值。</param>
    /// <returns>返回插值结果。</returns>
    public override string Interpolate(double progress, string oldValue, string newValue)
    {
        if (progress <= 0)
            return oldValue;
        if (progress >= 1)
            return newValue;
        int oldLength = string.IsNullOrEmpty(oldValue) ? 0 : oldValue.Length;
        int newLength = string.IsNullOrEmpty(newValue) ? 0 : newValue.Length;
        if (oldLength == 0 && newLength == 0)
            return string.Empty;
        if (oldLength == newLength && oldValue == newValue)
            return newValue;
        if (oldLength == 0 || newValue.StartsWith(oldValue))
        {
            // 如果旧值为空或新值以旧值开头，则从旧值开始插入新值的剩余部分
            return newValue.Substring(0, (int)(oldLength + (newLength - oldLength) * progress));
        }
        else if (newLength == 0 || oldValue.StartsWith(newValue))
        {
            // 如果新值为空或旧值以新值开头，则从新值开始删除旧值的剩余部分
            return oldValue.Substring(0, (int)(newLength + (oldLength - newLength) * (1 - progress)));
        }
        else
        {
            //如果没有包含关系，忽略旧值，直接从新值开始插入
            oldLength = 0;
            return newValue.Substring(0, (int)(oldLength + (newLength - oldLength) * progress));
        }
    }

    static StringAnimator()
    {
        // 注册动画器
        Animation.RegisterCustomAnimator<string, StringAnimator>();
    }
}

public class DiscreteAnimator<T> : InterpolatingAnimator<T>
{
    public override T Interpolate(double progress, T oldValue, T newValue)
    {
        return progress < 1 ? oldValue : newValue;
    }

    static DiscreteAnimator()
    {
        // 注册动画器
        Animation.RegisterCustomAnimator<T, DiscreteAnimator<T>>();
    }
}

<TextBlock Text="离散动画器文本，切换几种不同的样式。">
    <TextBlock.Styles>
        <Style Selector="TextBlock">
          <Style.Animations>
            <Animation Duration="0:0:3" IterationCount="Infinite" PlaybackDirection="Alternate">
              <KeyFrame Cue="0%">
                <Setter Property="FontStyle" Value="Normal">
                    <Animation.Animator>
                        <app:DiscreteAnimator x:TypeArguments="FontStyle" />
                    </Animation.Animator>
                </Setter>
              </KeyFrame>
              <KeyFrame Cue="30%">
                <Setter Property="FontStyle" Value="Italic">
                    <Animation.Animator>
                        <app:DiscreteAnimator x:TypeArguments="FontStyle" />
                    </Animation.Animator>
                </Setter>
              </KeyFrame>
              <KeyFrame Cue="60%">
                <Setter Property="FontStyle" Value="Oblique">
                    <Animation.Animator>
                        <app:DiscreteAnimator x:TypeArguments="FontStyle" />
                    </Animation.Animator>
                </Setter>
              </KeyFrame>
            </Animation>
          </Style.Animations>
        </Style>
      </TextBlock.Styles>
</TextBlock>

//注册一个AvaloniaProperty，类型为int，默认值为0
public const string DISCRETE_VALUE = "DiscreteValue";
public static readonly StyledProperty<int> DiscreteValueProperty =
    AvaloniaProperty.Register<Path, int>(DISCRETE_VALUE, 0);
//定义一个数组，存储不同的几何路径，在动画过程中根据DiscreteValue的值来切换不同的路径
private PathGeometry[] bells = [];      //这里省略了路径的定义
//创建一个动画并运行它
private void PlayAnimation_Click(object? sender, Avalonia.Interactivity.RoutedEventArgs e)
{
    var animation = new Animation()
    {
        Duration = TimeSpan.FromSeconds(8),
        IterationCount = new IterationCount(2),
        PlaybackDirection = PlaybackDirection.Alternate,
        Children =
        {
            new KeyFrame()
            {
                Setters = { new Setter(DiscreteValueProperty, 0), },
                KeyTime = TimeSpan.FromSeconds(0)
            },
            new KeyFrame()
            {
                Setters = { new Setter(DiscreteValueProperty, 1), },
                KeyTime = TimeSpan.FromSeconds(2)
            },
            new KeyFrame()
            {
                Setters = { new Setter(DiscreteValueProperty, 2), },
                KeyTime = TimeSpan.FromSeconds(4)
            },
            new KeyFrame()
            {
                Setters = { new Setter(DiscreteValueProperty, 3), },
                KeyTime = TimeSpan.FromSeconds(6)
            },
            new KeyFrame()
            {
                Setters = { new Setter(DiscreteValueProperty, 3), },
                KeyTime = TimeSpan.FromSeconds(8)
            }
        }
    };
    _ = animation.RunAsync(Path1);
}
//在属性的PropertyChanged事件中，根据DiscreteValue的值来切换不同的路径
private void Path1_PropertyChanged(object? sender, Avalonia.AvaloniaPropertyChangedEventArgs e)
{
    if (e.Property.Name == DiscreteValueProperty.Name)
    {
        Debug.WriteLine($"time: {DateTime.Now}, Path1 property changed: {e.Property.Name}, old value: {e.OldValue}, new value: {e.NewValue}");
        int value = (int)e.NewValue;
        Path1.Data = bells[value % bells.Length];
    }
}