如何使用淡入/淡出动画翻转视图窗口8 [c#/xaml]

WinRT XAML 工具包中的一个类，可用于通过简单的调用（如 myFlipView.FadeOut()）淡入/淡出。您可以将代码更改为如下所示的内容：

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
}

这个答案的目的是补充Filip Skakun的答案，因为错过了扩展BeginAsync。将如下所示的扩展嵌入到他的class UIElementAnimationExtensions后，它适用于我的情况。^_^

    public async static Task BeginAsync(this Storyboard myStoryboard)
    {
        SemaphoreSlim signal = new SemaphoreSlim(0, 1);
        EventHandler<object> eventHandler = new EventHandler<object>(
            (sender, args) => 
            {
                signal.Release();
            }
            );
        myStoryboard.Completed += eventHandler;
        myStoryboard.Begin();
        await signal.WaitAsync();
        myStoryboard.Completed -= eventHandler;
    }

顺便说一下，这个扩展的概念是基于答案 是否可以等待一个事件而不是另一个异步方法？.