/// <summary>
/// Updates the targeted index -- that is the index where the item will be moved to if dropped at this point.
/// </summary>
private void UpdateDropTargetIndex(ReorderListBoxItem targetItemContainer, bool after)
{
int dragItemIndex = this.Items.IndexOf(this.dragItem);
int targetItemIndex = this.Items.IndexOf(targetItemContainer.Content);
int newDropTargetIndex;
if (targetItemIndex == dragItemIndex)
{
newDropTargetIndex = dragItemIndex;
}
else
{
newDropTargetIndex = targetItemIndex + (after ? 1 : 0) - (targetItemIndex >= dragItemIndex ? 1 : 0);
}
if (newDropTargetIndex != this.dropTargetIndex)
{
this.dropTargetIndex = newDropTargetIndex;
}
}
/// <summary>
/// Called when the user presses down on the transparent drag-interceptor. Identifies the targed
/// drag handle and list item and prepares for a drag operation.
/// </summary>
private void dragInterceptor_ManipulationStarted(object sender, ManipulationStartedEventArgs e)
{
if (this.itemsPanel == null)
{
ItemsPresenter scrollItemsPresenter = (ItemsPresenter)this.scrollViewer.Content;
this.itemsPanel = (Panel)VisualTreeHelper.GetChild(scrollItemsPresenter, 0);
}
GeneralTransform interceptorTransform = this.dragInterceptor.TransformToVisual(
Application.Current.RootVisual);
Point targetPoint = interceptorTransform.Transform(e.ManipulationOrigin);
targetPoint = ReorderListBox.GetHostCoordinates(targetPoint);
List<UIElement> targetElements = VisualTreeHelper.FindElementsInHostCoordinates(
targetPoint, this.itemsPanel).ToList();
ReorderListBoxItem targetItemContainer = targetElements.OfType<ReorderListBoxItem>().FirstOrDefault();
if (targetItemContainer != null && targetElements.Contains(targetItemContainer.DragHandle))
{
VisualStateManager.GoToState(targetItemContainer, ReorderListBoxItem.DraggingState, true);
GeneralTransform targetItemTransform = targetItemContainer.TransformToVisual(this.dragInterceptor);
Point targetItemOrigin = targetItemTransform.Transform(new Point(0, 0));
Canvas.SetLeft(this.dragIndicator, targetItemOrigin.X);
Canvas.SetTop(this.dragIndicator, targetItemOrigin.Y);
this.dragIndicator.Width = targetItemContainer.RenderSize.Width;
this.dragIndicator.Height = targetItemContainer.RenderSize.Height;
this.dragItemContainer = targetItemContainer;
this.dragItem = this.dragItemContainer.Content;
this.dragInterceptorRect = interceptorTransform.TransformBounds(
new Rect(new Point(0, 0), this.dragInterceptor.RenderSize));
this.dropTargetIndex = -1;
}
}
/// <summary>
/// Ensures that a possibly-recycled item container (ReorderListBoxItem) is ready to display a list item.
/// </summary>
protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
{
base.PrepareContainerForItemOverride(element, item);
ReorderListBoxItem itemContainer = (ReorderListBoxItem)element;
itemContainer.ApplyTemplate(); // Loads visual states.
// Set this state before binding to avoid showing the visual transition in this case.
string reorderState = this.IsReorderEnabled ?
ReorderListBoxItem.ReorderEnabledState : ReorderListBoxItem.ReorderDisabledState;
VisualStateManager.GoToState(itemContainer, reorderState, false);
itemContainer.SetBinding(ReorderListBoxItem.IsReorderEnabledProperty,
new Binding(ReorderListBox.IsReorderEnabledPropertyName) { Source = this });
if (item == this.dragItem)
{
VisualStateManager.GoToState(itemContainer, ReorderListBoxItem.DraggingState, false);
if (this.dropTargetIndex >= 0)
{
// The item's dragIndicator is currently being moved, so the item itself is hidden.
itemContainer.Visibility = Visibility.Collapsed;
this.dragItemContainer = itemContainer;
}
else
{
// The item was just moved and dropped, so it needs to be transitioned back to not-dragging state.
VisualStateManager.GoToState(itemContainer, ReorderListBoxItem.NotDraggingState, true);
this.dragItem = null;
}
}
else
{
VisualStateManager.GoToState(itemContainer, ReorderListBoxItem.NotDraggingState, false);
}
}
/// <summary>
/// Called when the user releases a drag. Moves the item within the source list and then resets everything.
/// </summary>
private void dragInterceptor_ManipulationCompleted(object sender, ManipulationCompletedEventArgs e)
{
if (this.dragItem == null)
{
return;
}
this.dragIndicator.Visibility = Visibility.Collapsed;
((TranslateTransform)this.dragIndicator.RenderTransform).Y = 0;
this.dragIndicator.Source = null;
if (this.dropTargetIndex >= 0)
{
this.MoveItem(this.dragItem, this.dropTargetIndex);
}
if (this.dragItemContainer != null)
{
this.dragItemContainer.Visibility = Visibility.Visible;
VisualStateManager.GoToState(this.dragItemContainer, ReorderListBoxItem.NotDraggingState, true);
this.dragItemContainer = null;
this.dragItem = null;
}
this.dragScrollDelta = 0;
this.dropTargetIndex = -1;
this.ClearDropTarget();
}
/// <summary>
/// Called when an item container (ReorderListBoxItem) is being removed from the list panel.
/// This may be because the item was removed from the list or because the item is now outside
/// the virtualization region (because ListBox uses a VirtualizingStackPanel as its items panel).
/// </summary>
protected override void ClearContainerForItemOverride(DependencyObject element, object item)
{
base.ClearContainerForItemOverride(element, item);
ReorderListBoxItem itemContainer = (ReorderListBoxItem)element;
if (itemContainer == this.dragItemContainer)
{
this.dragItemContainer.Visibility = Visibility.Visible;
this.dragItemContainer = null;
}
}
