WPF中自定义GridLengthAnimation

public class GridLengthAnimation : AnimationTimeline  {    /// <summary>    /// Returns the type of object to animate    /// </summary>    public override Type TargetPropertyType => typeof(GridLength);     /// <summary>    /// Creates an instance of the animation object    /// </summary>    /// <returns>Returns the instance of the GridLengthAnimation</returns>    protected override System.Windows.Freezable CreateInstanceCore()    {      return new GridLengthAnimation();    }     /// <summary>    /// Dependency property for the From property    /// </summary>    public static readonly DependencyProperty FromProperty = DependencyProperty.Register("From", typeof(GridLength),      typeof(GridLengthAnimation));     /// <summary>    /// CLR Wrapper for the From depenendency property    /// </summary>    public GridLength From    {      get      {        return (GridLength)GetValue(GridLengthAnimation.FromProperty);      }      set      {        SetValue(GridLengthAnimation.FromProperty, value);      }    }     /// <summary>    /// Dependency property for the To property    /// </summary>    public static readonly DependencyProperty ToProperty = DependencyProperty.Register("To", typeof(GridLength),      typeof(GridLengthAnimation));     /// <summary>    /// CLR Wrapper for the To property    /// </summary>    public GridLength To    {      get      {        return (GridLength)GetValue(GridLengthAnimation.ToProperty);      }      set      {        SetValue(GridLengthAnimation.ToProperty, value);      }    }     /// <summary>    /// Animates the grid let set    /// </summary>    /// <param name="defaultOriginValue">The original value to animate</param>    /// <param name="defaultDestinationValue">The final value</param>    /// <param name="animationClock">The animation clock (timer)</param>    /// <returns>Returns the new grid length to set</returns>    public override object GetCurrentValue(object defaultOriginValue,      object defaultDestinationValue, AnimationClock animationClock)    {      double fromVal = ((GridLength)GetValue(GridLengthAnimation.FromProperty)).Value;       double toVal = ((GridLength)GetValue(GridLengthAnimation.ToProperty)).Value;       if (fromVal > toVal)        return new GridLength((1 - animationClock.CurrentProgress.Value) * (fromVal - toVal) + toVal, GridUnitType.Star);      else        return new GridLength(animationClock.CurrentProgress.Value * (toVal - fromVal) + fromVal, GridUnitType.Star);    }

 /// <summary>    /// The <see cref="EasingFunction" /> dependency property's name.    /// </summary>    public const string EasingFunctionPropertyName = "EasingFunction";     /// <summary>    /// Gets or sets the value of the <see cref="EasingFunction" />    /// property. This is a dependency property.    /// </summary>    public IEasingFunction EasingFunction    {      get      {        return (IEasingFunction)GetValue(EasingFunctionProperty);      }      set      {        SetValue(EasingFunctionProperty, value);      }    }     /// <summary>    /// Identifies the <see cref="EasingFunction" /> dependency property.    /// </summary>    public static readonly DependencyProperty EasingFunctionProperty = DependencyProperty.Register(      EasingFunctionPropertyName,      typeof(IEasingFunction),      typeof(GridLengthAnimation),      new UIPropertyMetadata(null));

public override object GetCurrentValue(object defaultOriginValue,      object defaultDestinationValue, AnimationClock animationClock)    {      double fromVal = ((GridLength)GetValue(FromProperty)).Value;       double toVal = ((GridLength)GetValue(ToProperty)).Value;       //check that from was set from the caller      //if (fromVal == 1)      //  //set the from as the actual value      //  fromVal = ((GridLength)defaultDestinationValue).Value;       double progress = animationClock.CurrentProgress.Value;       IEasingFunction easingFunction = EasingFunction;      if (easingFunction != null)      {        progress = easingFunction.Ease(progress);      }        if (fromVal > toVal)        return new GridLength((1 - progress) * (fromVal - toVal) + toVal, GridUnitType.Star);         return new GridLength(progress * (toVal - fromVal) + fromVal, GridUnitType.Star);    }

 <anim:GridLengthAnimation Storyboard.TargetProperty="Width" From="0" To="*" Duration="0:0:0.5"/>