需求
我们想在编辑一个列表中某一个条目时，将编辑的详情内容也放置当前面，比如右侧。
可以通过将一个Grid,分成两个Cloumn,动态调整两个Cloumn的Width，就可以实现这个需求。
我们知道，Clomun的Width是个，而默认的动画没有这样子的。我们就需要自己实现这样一人动画。
设计
我们从Animation的类图上看到
我们可以从需求
我们想在编辑一个列表中某一个条目时，将编辑的详情内容也放置当前面，比如右侧。
可以通过将一个Grid,分成两个Cloumn,动态调整两个Cloumn的Width，就可以实现这个需求。
我们知道，Clomun的Width是个GridLength，而默认的动画没有这样子的。我们就需要自己实现这样一人动画。
设计
我们从Animation的类图上看到AnimationTimeline继承，重写其GetCurrentValue
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);
}
如上所示，我们仿着默认动画实现了From,To,同时将其属性定义为GridLength,当动画执行时，我们重写了GetCurrentValue,使其根据From/To属性相关联。
优化
通过以上代码，我们实现了在GridLength变化时，实现动画。但是，试用后我们发现，动画，有点太线性。这个时候，怎么办？
可以通过引入EasingFunction来实现。我们知道EasingFunction其实就是一个与时间t有关的时间函数f(t).通过时间函数的处理，我们使动画过渡不要那么线性。
/// <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));
对应的，还要重写GetCurrentValue函数。
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);
}
使用
<anim:GridLengthAnimation Storyboard.TargetProperty="Width" From="0" To="*" Duration="0:0:0.5"/>
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