private void OnSelectedItemsChanged(SelectionChangedEventArgs args)
{
//Logic - by default when items scroll out of view they are no longer selected.
//this is because the panel is virtualised and and automatically unselected due
//to the control thinking that the item is not longer part of the overall collection
if (_isSelecting) return;
try
{
_isSelecting = true;
_selected.Edit(innerList =>
{
var toAdd = args.AddedItems.OfType<LineProxy>().ToList();
//may need to track if last selected is off the page:
var isShiftKeyDown = Keyboard.IsKeyDown(Key.LeftShift) || Keyboard.IsKeyDown(Key.RightShift);
//get the last item at then end of the list
if (!isShiftKeyDown)
{
//if mouse down, we need to prevent items being cleated
//add items to list
foreach (var lineProxy in toAdd)
{
if (innerList.Contains(lineProxy)) continue;
_lastSelected = lineProxy;
innerList.Add(lineProxy);
}
}
else
{
if (_lastSelected == null)
{
foreach (var lineProxy in toAdd)
{
if (innerList.Contains(lineProxy)) continue;
_lastSelected = lineProxy;
innerList.Add(lineProxy);
}
args.Handled = true;
return;
}
//if shift down we need to override selected and manually select our selves
var last = _lastSelected.Index;
var allSelectedItems = _selector.SelectedItems.OfType<LineProxy>().ToArray();
var currentPage = _selector.Items.OfType<LineProxy>().ToArray();
//1. Determine whether all selected items are on the current page [plus whether last is on the current page]
var allOnCurrentPage = allSelectedItems.Intersect(currentPage).ToArray();
var lastInONcurrentPage = currentPage.Contains(_lastSelected);
if (lastInONcurrentPage && allOnCurrentPage.Length == allSelectedItems.Length)
{
innerList.Clear();
innerList.AddRange(allSelectedItems);
return;
}
args.Handled = true;
var maxOfRecent = toAdd.Max(lp => lp.Index);
int min;
int max;
if (last < maxOfRecent)
{
min = last;
max = maxOfRecent;
}
else
{
min = maxOfRecent;
max = last;
}
//maintain selection
_selector.SelectedItems.Clear();
var fromCurrentPage = _selector.Items.OfType<LineProxy>()
.Where(lp => lp.Index >= min && lp.Index <= max)
.ToArray();
var fromPrevious = _recentlyRemovedFromVisibleRange
.Items.Where(lp => lp.Index >= min && lp.Index <= max)
.ToArray();
_recentlyRemovedFromVisibleRange.Clear();
//maintain our record
innerList.Clear();
innerList.AddRange(fromCurrentPage);
foreach (var previous in fromPrevious)
{
if (!innerList.Contains(previous))
innerList.Add(previous);
}
//finally reload the actual selection:
foreach (var item in innerList)
{
_selector.SelectedItems.Add(item);
}
}
});
}
catch (Exception ex)
{
_logger.Error(ex,"There has been a problem with manual selection");
}
finally
{
_isSelecting = false;
}
}
private void ClearAllSelections()
{
_selected.Clear();
_recentlyRemovedFromVisibleRange.Clear();
_lastSelected = null;
}