淡入很容易,但是对于淡出,项目需要在动画完成之前保留在源列表中(就像你所说的)。
如果我们仍然希望能够正常使用源ObservableCollection(添加/删除等),那么我们必须创建一个镜像集合,该集合与源集合始终保持同步,并延迟删除直到动画完成。这可以使用CollectionChanged事件完成。
以下是我使用附加行为实现的实现。它可用于ItemsControl、ListBox、DataGrid或任何其他从ItemsControl派生的内容。
不要绑定ItemsSource,而是绑定附加属性ItemsSourceBehavior.ItemsSource。它将使用Reflection创建一个镜像ObservableCollection,将其用作ItemsSource并处理FadeIn/FadeOut动画。
请注意,我没有对此进行广泛测试,可能存在错误和多个可以改进的地方,但在我的场景中效果非常好。
示例用法
<ListBox behaviors:ItemsSourceBehavior.ItemsSource="{Binding MyCollection}">
<behaviors:ItemsSourceBehavior.FadeInAnimation>
<Storyboard>
<DoubleAnimation Storyboard.TargetProperty="Opacity"
From="0.0"
To="1.0"
Duration="0:0:3"/>
</Storyboard>
</behaviors:ItemsSourceBehavior.FadeInAnimation>
<behaviors:ItemsSourceBehavior.FadeOutAnimation>
<Storyboard>
<DoubleAnimation Storyboard.TargetProperty="Opacity"
To="0.0"
Duration="0:0:1"/>
</Storyboard>
</behaviors:ItemsSourceBehavior.FadeOutAnimation>
<!
</ListBox>
ItemsSourceBehavior
public class ItemsSourceBehavior
{
public static readonly DependencyProperty ItemsSourceProperty =
DependencyProperty.RegisterAttached("ItemsSource",
typeof(IList),
typeof(ItemsSourceBehavior),
new UIPropertyMetadata(null, ItemsSourcePropertyChanged));
public static void SetItemsSource(DependencyObject element, IList value)
{
element.SetValue(ItemsSourceProperty, value);
}
public static IList GetItemsSource(DependencyObject element)
{
return (IList)element.GetValue(ItemsSourceProperty);
}
private static void ItemsSourcePropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
ItemsControl itemsControl = source as ItemsControl;
IList itemsSource = e.NewValue as IList;
if (itemsControl == null)
{
return;
}
if (itemsSource == null)
{
itemsControl.ItemsSource = null;
return;
}
Type itemsSourceType = itemsSource.GetType();
Type listType = typeof(ObservableCollection<>).MakeGenericType(itemsSourceType.GetGenericArguments()[0]);
IList mirrorItemsSource = (IList)Activator.CreateInstance(listType);
itemsControl.SetBinding(ItemsControl.ItemsSourceProperty, new Binding{ Source = mirrorItemsSource });
foreach (object item in itemsSource)
{
mirrorItemsSource.Add(item);
}
FadeInContainers(itemsControl, itemsSource);
(itemsSource as INotifyCollectionChanged).CollectionChanged +=
(object sender, NotifyCollectionChangedEventArgs ne) =>
{
if (ne.Action == NotifyCollectionChangedAction.Add)
{
foreach (object newItem in ne.NewItems)
{
mirrorItemsSource.Add(newItem);
}
FadeInContainers(itemsControl, ne.NewItems);
}
else if (ne.Action == NotifyCollectionChangedAction.Remove)
{
foreach (object oldItem in ne.OldItems)
{
UIElement container = itemsControl.ItemContainerGenerator.ContainerFromItem(oldItem) as UIElement;
Storyboard fadeOutAnimation = GetFadeOutAnimation(itemsControl);
if (container != null && fadeOutAnimation != null)
{
Storyboard.SetTarget(fadeOutAnimation, container);
EventHandler onAnimationCompleted = null;
onAnimationCompleted = ((sender2, e2) =>
{
fadeOutAnimation.Completed -= onAnimationCompleted;
mirrorItemsSource.Remove(oldItem);
});
fadeOutAnimation.Completed += onAnimationCompleted;
fadeOutAnimation.Begin();
}
else
{
mirrorItemsSource.Remove(oldItem);
}
}
}
};
}
private static void FadeInContainers(ItemsControl itemsControl, IList newItems)
{
EventHandler statusChanged = null;
statusChanged = new EventHandler(delegate
{
if (itemsControl.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
{
itemsControl.ItemContainerGenerator.StatusChanged -= statusChanged;
foreach (object newItem in newItems)
{
UIElement container = itemsControl.ItemContainerGenerator.ContainerFromItem(newItem) as UIElement;
Storyboard fadeInAnimation = GetFadeInAnimation(itemsControl);
if (container != null && fadeInAnimation != null)
{
Storyboard.SetTarget(fadeInAnimation, container);
fadeInAnimation.Begin();
}
}
}
});
itemsControl.ItemContainerGenerator.StatusChanged += statusChanged;
}
public static readonly DependencyProperty FadeInAnimationProperty =
DependencyProperty.RegisterAttached("FadeInAnimation",
typeof(Storyboard),
typeof(ItemsSourceBehavior),
new UIPropertyMetadata(null));
public static void SetFadeInAnimation(DependencyObject element, Storyboard value)
{
element.SetValue(FadeInAnimationProperty, value);
}
public static Storyboard GetFadeInAnimation(DependencyObject element)
{
return (Storyboard)element.GetValue(FadeInAnimationProperty);
}
public static readonly DependencyProperty FadeOutAnimationProperty =
DependencyProperty.RegisterAttached("FadeOutAnimation",
typeof(Storyboard),
typeof(ItemsSourceBehavior),
new UIPropertyMetadata(null));
public static void SetFadeOutAnimation(DependencyObject element, Storyboard value)
{
element.SetValue(FadeOutAnimationProperty, value);
}
public static Storyboard GetFadeOutAnimation(DependencyObject element)
{
return (Storyboard)element.GetValue(FadeOutAnimationProperty);
}
}