// If the types of the dragged data and ItemsControl's source are compatible,
// there are 3 situations to have into account when deciding the drop target:
// 1. mouse is over an items container
// 2. mouse is over the empty part of an ItemsControl, but ItemsControl is not empty
// 3. mouse is over an empty ItemsControl.
// The goal of this method is to decide on the values of the following properties:
// targetItemContainer, insertionIndex and isInFirstHalf.
private void DecideDropTarget(DragEventArgs e, object draggedItem)
{
_isInFirstHalf = false;
_targetItemContainer = null;
_targetOrientation = Orientation.Vertical;
_targetInsertionIndex = -1;
if (!IsDropDataAllowed(draggedItem))
{
// Mismatched type
e.Effects = DragDropEffects.None;
return;
}
var targetItemsControlCount = _targetItemsControl.Items.Count;
if (targetItemsControlCount == 0)
{
// Over an empty items control, insert at the beginning
_targetInsertionIndex = 0;
return;
}
// Find the items panel
_targetOrientation = DragDropUtilities.GetOrientation(
_targetItemsControl.ItemContainerGenerator.ContainerFromIndex(0),
GetDefaultOrientation(_targetItemsControl));
// This is the element we are pointing to (as long as it has a background)
_targetItemContainer = _targetItemsControl.ContainerFromElement((DependencyObject)e.OriginalSource) as FrameworkElement;
if (_targetItemContainer != null)
{
var positionRelativeToItemContainer = e.GetPosition(_targetItemContainer);
_isInFirstHalf = DragDropUtilities.IsInFirstHalf(_targetItemContainer, positionRelativeToItemContainer, _targetOrientation);
_targetInsertionIndex = _targetItemsControl.ItemContainerGenerator.IndexFromContainer(_targetItemContainer);
if (!_isInFirstHalf)
{
// Insert after the target if more than half way through
_targetInsertionIndex++;
}
return;
}
// Fallback to the last item in the container (always show at bottom)
_targetItemContainer = _targetItemsControl.ItemContainerGenerator.ContainerFromIndex(targetItemsControlCount - 1) as FrameworkElement;
_targetInsertionIndex = targetItemsControlCount;
}
private void DropTarget_Drop(object sender, DragEventArgs e)
{
e.Handled = true;
var draggedItem = e.Data.GetData(_format.Name);
if (draggedItem == null)
{
return;
}
var indexRemoved = -1;
if ((e.Effects & DragDropEffects.Move) != 0)
{
indexRemoved = DragDropUtilities.RemoveItemFromItemsControl(_sourceItemsControl, draggedItem);
}
// This happens when we drag an item to a later position within the same ItemsControl.
if (indexRemoved != -1 && _sourceItemsControl == _targetItemsControl && indexRemoved < _targetInsertionIndex)
{
_targetInsertionIndex--;
}
DragDropUtilities.InsertItemIntoItemsControl(_targetItemsControl, draggedItem, _targetInsertionIndex);
RemoveDraggedAdorner();
RemoveInsertionAdorner();
}
// Drag = mouse down + move by a certain amount
private void DragSource_PreviewMouseMove(object sender, MouseEventArgs e)
{
if (_draggedData == null)
{
return;
}
// Only drag when user moved the mouse by a reasonable amount.
if (!DragDropUtilities.IsMovementBigEnough(_initialMousePosition, e.GetPosition(_sourceItemsControl)))
{
return;
}
// Definately was our event
e.Handled = true;
// Get the data ready to be dropped
var data = new DataObject(_format.Name, _draggedData);
// From now on, get the data from the DataObject
_draggedData = null;
// Adding events to the parent to make sure the dragged adorner comes up when mouse is not over a drop target
var parent = GetDragParent(_sourceItemsControl);
DependencyProperty backgroundProperty = null;
bool setBackground = false;
bool previousAllowDrop = false;
if (parent != null)
{
backgroundProperty = DragDropUtilities.GetDependencyPropertyByName(parent.GetType(), "BackgroundProperty");
// If the parent does not draw a background (like a grid by default) then you will not get drag events
// Unfortunately Background is defined in several classes e.g. Control, Panel not a single base class
// so use reflection to get and set the current value
if (backgroundProperty != null)
{
var background = parent.GetValue(backgroundProperty) as Brush;
if (background == null)
{
parent.SetValue(backgroundProperty, Brushes.Transparent);
setBackground = true;
}
previousAllowDrop = parent.AllowDrop;
parent.AllowDrop = true;
parent.DragEnter += Parent_DragEnter;
parent.DragOver += Parent_DragOver;
parent.DragLeave += Parent_DragLeave;
}
}
var effects = DragDrop.DoDragDrop((DependencyObject)sender, data, DragDropEffects.Move);
// Without this call, there would be a bug in the following scenario: Click on a data item, and drag
// the mouse very fast outside of the window. When doing this really fast, for some reason I don't get
// the Window leave event, and the dragged adorner is left behind.
// With this call, the dragged adorner will disappear when we release the mouse outside of the window,
// which is when the DoDragDrop synchronous method returns.
RemoveDraggedAdorner();
if (parent != null)
{
if (backgroundProperty != null)
{
if (setBackground)
{
parent.ClearValue(backgroundProperty);
setBackground = false;
}
parent.AllowDrop = previousAllowDrop;
parent.DragEnter -= Parent_DragEnter;
parent.DragOver -= Parent_DragOver;
parent.DragLeave -= Parent_DragLeave;
}
}
}