另一种可能的方法是创建一个自定义动画类来为画笔设置动画。
我找到了一种简单的方法，方法是创建一个派生自AnimationTimeline 的类。我们可以覆盖自定义类中的一些成员，其中包括AnimationTimeline.GetCurrentValue method。它返回一个取决于动画进度以及开始和结束值的值。
最简单的方法是创建一个VisualBrush 并使用子控件上的Opacity 属性交叉淡入淡出开始值和结束值。结果是一个类似下面的类：
public class BrushAnimation : AnimationTimeline
{
public override Type TargetPropertyType
{
get
{
return typeof(Brush);
}
}
public override object GetCurrentValue(object defaultOriginValue,
object defaultDestinationValue,
AnimationClock animationClock)
{
return GetCurrentValue(defaultOriginValue as Brush,
defaultDestinationValue as Brush,
animationClock);
}
public object GetCurrentValue(Brush defaultOriginValue,
Brush defaultDestinationValue,
AnimationClock animationClock)
{
if (!animationClock.CurrentProgress.HasValue)
return Brushes.Transparent;
//use the standard values if From and To are not set
//(it is the value of the given property)
defaultOriginValue = this.From ?? defaultOriginValue;
defaultDestinationValue = this.To ?? defaultDestinationValue;
if (animationClock.CurrentProgress.Value == 0)
return defaultOriginValue;
if (animationClock.CurrentProgress.Value == 1)
return defaultDestinationValue;
return new VisualBrush(new Border()
{
Width = 1,
Height = 1,
Background = defaultOriginValue,
Child = new Border()
{
Background = defaultDestinationValue,
Opacity = animationClock.CurrentProgress.Value,
}
});
}
protected override Freezable CreateInstanceCore()
{
return new BrushAnimation();
}
//we must define From and To, AnimationTimeline does not have this properties
public Brush From
{
get { return (Brush)GetValue(FromProperty); }
set { SetValue(FromProperty, value); }
}
public Brush To
{
get { return (Brush)GetValue(ToProperty); }
set { SetValue(ToProperty, value); }
}
public static readonly DependencyProperty FromProperty =
DependencyProperty.Register("From", typeof(Brush), typeof(BrushAnimation));
public static readonly DependencyProperty ToProperty =
DependencyProperty.Register("To", typeof(Brush), typeof(BrushAnimation));
}
您可以像往常一样在 XAML 中使用它：
<EventTrigger RoutedEvent="Loaded">
<BeginStoryboard>
<Storyboard >
<local:BrushAnimation Storyboard.TargetName="border"
Storyboard.TargetProperty="Background"
Duration="0:0:5" From="Red"
RepeatBehavior="Forever" AutoReverse="True" >
<local:BrushAnimation.To>
<LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
<GradientStop Color="#FF00FF2E" Offset="0.005"/>
<GradientStop Color="#FFC5FF00" Offset="1"/>
<GradientStop Color="Blue" Offset="0.43"/>
</LinearGradientBrush>
</local:BrushAnimation.To>
</local:BrushAnimation>
</Storyboard>
</BeginStoryboard>
</EventTrigger>
或在后面的代码中：
var animation = new BrushAnimation
{
From = Brushes.Red,
To = new LinearGradientBrush (Colors.Green, Colors.Yellow, 45),
Duration = new Duration(TimeSpan.FromSeconds(5)),
};
animation.Completed += new EventHandler(animation_Completed);
Storyboard.SetTarget(animation, border);
Storyboard.SetTargetProperty(animation, new PropertyPath("Background"));
var sb = new Storyboard();
sb.Children.Add(animation);
sb.Begin();
还可以使用构造函数重载等来扩展BrushAnimation，因此它看起来像一个 .NET 给定的动画类型。