/// <summary>
/// Slides the drag indicator (item snapshot) to the location of the dropped item,
/// then performs the visibility swap and removes the dragging visual state.
/// </summary>
private void AnimateDrop(ReorderListBoxItem itemContainer)
{
GeneralTransform itemTransform = itemContainer.TransformToVisual(this.dragInterceptor);
Rect itemRect = itemTransform.TransformBounds(new Rect(new Point(0, 0), itemContainer.RenderSize));
double delta = Math.Abs(itemRect.Y - Canvas.GetTop(this.dragIndicator) -
((TranslateTransform)this.dragIndicator.RenderTransform).Y);
if (delta > 0)
{
// Adjust the duration based on the distance, so the speed will be constant.
TimeSpan duration = TimeSpan.FromSeconds(0.25 * delta / itemRect.Height);
Storyboard dropStoryboard = new Storyboard();
DoubleAnimation moveToDropAnimation = new DoubleAnimation();
Storyboard.SetTarget(moveToDropAnimation, this.dragIndicator.RenderTransform);
Storyboard.SetTargetProperty(moveToDropAnimation, new PropertyPath(TranslateTransform.YProperty));
moveToDropAnimation.To = itemRect.Y - Canvas.GetTop(this.dragIndicator);
moveToDropAnimation.Duration = duration;
dropStoryboard.Children.Add(moveToDropAnimation);
dropStoryboard.Completed += delegate
{
this.dragItem = null;
itemContainer.Opacity = 1;
this.dragIndicator.Visibility = Visibility.Collapsed;
this.dragIndicator.Source = null;
((TranslateTransform)this.dragIndicator.RenderTransform).Y = 0;
VisualStateManager.GoToState(itemContainer, ReorderListBoxItem.NotDraggingState, true);
};
dropStoryboard.Begin();
}
else
{
// There was no need for an animation, so do the visibility swap right now.
this.dragItem = null;
itemContainer.Opacity = 1;
this.dragIndicator.Visibility = Visibility.Collapsed;
this.dragIndicator.Source = null;
VisualStateManager.GoToState(itemContainer, ReorderListBoxItem.NotDraggingState, true);
}
}