这是 WinRT XAML 工具包中的一个类，您可以使用它通过简单的调用（如myFlipView.FadeOut(). 您可以将代码更改为以下内容：
private async void ChangeItems(object sender, object o)
{
var totalItems = TheFlipView.Items.Count;
var newItemIndex = (TheFlipView.SelectedIndex + 1) % totalItems;
await TheFlipView.FadeOut();
TheFlipView.SelectedIndex = newItemIndex;
TheFlipView.FadeIn();
}
扩展类：
public static class UIElementAnimationExtensions
{
#region AttachedFadeStoryboard
/// <summary>
/// AttachedFadeStoryboard Attached Dependency Property
/// </summary>
public static readonly DependencyProperty AttachedFadeStoryboardProperty =
DependencyProperty.RegisterAttached(
"AttachedFadeStoryboard",
typeof(Storyboard),
typeof(UIElementAnimationExtensions),
new PropertyMetadata(null, OnAttachedFadeStoryboardChanged));
/// <summary>
/// Gets the AttachedFadeStoryboard property. This dependency property
/// indicates the currently running custom fade in/out storyboard.
/// </summary>
private static Storyboard GetAttachedFadeStoryboard(DependencyObject d)
{
return (Storyboard)d.GetValue(AttachedFadeStoryboardProperty);
}
/// <summary>
/// Sets the AttachedFadeStoryboard property. This dependency property
/// indicates the currently running custom fade in/out storyboard.
/// </summary>
private static void SetAttachedFadeStoryboard(DependencyObject d, Storyboard value)
{
d.SetValue(AttachedFadeStoryboardProperty, value);
}
/// <summary>
/// Handles changes to the AttachedFadeStoryboard property.
/// </summary>
/// <param name="d">
/// The <see cref="DependencyObject"/> on which
/// the property has changed value.
/// </param>
/// <param name="e">
/// Event data that is issued by any event that
/// tracks changes to the effective value of this property.
/// </param>
private static void OnAttachedFadeStoryboardChanged(
DependencyObject d, DependencyPropertyChangedEventArgs e)
{
Storyboard oldAttachedFadeStoryboard = (Storyboard)e.OldValue;
Storyboard newAttachedFadeStoryboard = (Storyboard)d.GetValue(AttachedFadeStoryboardProperty);
}
#endregion
#region FadeIn()
/// <summary>
/// Fades the element in using the FadeInThemeAnimation.
/// </summary>
/// <remarks>
/// Opacity property of the element is not affected.<br/>
/// The duration of the visible animation itself is not affected by the duration parameter. It merely indicates how long the Storyboard will run.<br/>
/// If FadeOutThemeAnimation was not used on the element before - nothing will happen.<br/>
/// </remarks>
/// <param name="element"></param>
/// <param name="duration"></param>
/// <returns></returns>
public static async Task FadeIn(this UIElement element, TimeSpan? duration = null)
{
((FrameworkElement)element).Visibility = Visibility.Visible;
var fadeInStoryboard = new Storyboard();
var fadeInAnimation = new FadeInThemeAnimation();
if (duration != null)
{
fadeInAnimation.Duration = duration.Value;
}
Storyboard.SetTarget(fadeInAnimation, element);
fadeInStoryboard.Children.Add(fadeInAnimation);
await fadeInStoryboard.BeginAsync();
}
#endregion
#region FadeOut()
/// <summary>
/// Fades the element out using the FadeOutThemeAnimation.
/// </summary>
/// <remarks>
/// Opacity property of the element is not affected.<br/>
/// The duration of the visible animation itself is not affected by the duration parameter. It merely indicates how long the Storyboard will run.<br/>
/// If FadeOutThemeAnimation was already run before and FadeInThemeAnimation was not run after that - nothing will happen.<br/>
/// </remarks>
/// <param name="element"></param>
/// <param name="duration"></param>
/// <returns></returns>
public static async Task FadeOut(this UIElement element, TimeSpan? duration = null)
{
var fadeOutStoryboard = new Storyboard();
var fadeOutAnimation = new FadeOutThemeAnimation();
if (duration != null)
{
fadeOutAnimation.Duration = duration.Value;
}
Storyboard.SetTarget(fadeOutAnimation, element);
fadeOutStoryboard.Children.Add(fadeOutAnimation);
await fadeOutStoryboard.BeginAsync();
}
#endregion
#region FadeInCustom()
/// <summary>
/// Fades the element in using a custom DoubleAnimation of the Opacity property.
/// </summary>
/// <param name="element"></param>
/// <param name="duration"></param>
/// <param name="easingFunction"> </param>
/// <returns></returns>
public static async Task FadeInCustom(this UIElement element, TimeSpan? duration = null, EasingFunctionBase easingFunction = null, double targetOpacity = 1.0)
{
CleanUpPreviousFadeStoryboard(element);
var fadeInStoryboard = new Storyboard();
var fadeInAnimation = new DoubleAnimation();
if (duration == null)
duration = TimeSpan.FromSeconds(0.4);
fadeInAnimation.Duration = duration.Value;
fadeInAnimation.To = targetOpacity;
fadeInAnimation.EasingFunction = easingFunction;
Storyboard.SetTarget(fadeInAnimation, element);
Storyboard.SetTargetProperty(fadeInAnimation, "Opacity");
fadeInStoryboard.Children.Add(fadeInAnimation);
SetAttachedFadeStoryboard(element, fadeInStoryboard);
await fadeInStoryboard.BeginAsync();
element.Opacity = targetOpacity;
fadeInStoryboard.Stop();
}
#endregion
#region FadeOutCustom()
/// <summary>
/// Fades the element out using a custom DoubleAnimation of the Opacity property.
/// </summary>
/// <param name="element"></param>
/// <param name="duration"></param>
/// <param name="easingFunction"> </param>
/// <returns></returns>
public static async Task FadeOutCustom(this UIElement element, TimeSpan? duration = null, EasingFunctionBase easingFunction = null)
{
CleanUpPreviousFadeStoryboard(element);
var fadeOutStoryboard = new Storyboard();
var fadeOutAnimation = new DoubleAnimation();
if (duration == null)
duration = TimeSpan.FromSeconds(0.4);
fadeOutAnimation.Duration = duration.Value;
fadeOutAnimation.To = 0.0;
fadeOutAnimation.EasingFunction = easingFunction;
Storyboard.SetTarget(fadeOutAnimation, element);
Storyboard.SetTargetProperty(fadeOutAnimation, "Opacity");
fadeOutStoryboard.Children.Add(fadeOutAnimation);
SetAttachedFadeStoryboard(element, fadeOutStoryboard);
await fadeOutStoryboard.BeginAsync();
element.Opacity = 0.0;
fadeOutStoryboard.Stop();
}
#endregion
#region CleanUpPreviousFadeStoryboard()
public static void CleanUpPreviousFadeStoryboard(this UIElement element)
{
var attachedFadeStoryboard = GetAttachedFadeStoryboard(element);
if (attachedFadeStoryboard != null)
{
attachedFadeStoryboard.Stop();
}
}
#endregion
}