/// <summary>
/// Updates the tree if items were removed from an observed
/// child collection. This might cause rendered tree nodes
/// to be removed. In case lazy loading is enabled, the update
/// of the UI may be as subtle as to remove an expander from
/// a collapsed node if the represented item's childs were
/// removed.
/// </summary>
/// <param name="observed">The observed collection.</param>
/// <param name="e">The event arguments that provide the
/// removed items.</param>
private void HandleRemovedChildItems(ICollection <T> observed, NotifyCollectionChangedEventArgs e)
{
IList childs = e.OldItems;
if (childs.Count == 0)
{
return;
}
//get the node of the parent item that contains the evented childs
TreeViewItem parentNode = GetParentNode((T)childs[0], observed);
if (parentNode == null)
{
return;
}
foreach (T childItem in childs)
{
string itemKey = tree.GetItemKey(childItem);
//check if we have a corresponding open node
//-> not necessarily the case if we're doing lazy loading
TreeViewItem childNode;
childNode = tree.TryFindItemNode(parentNode.Items, itemKey, false);
if (childNode != null)
{
//unregister listeners
UnregisterListeners(childNode);
//remove node from UI
parentNode.Items.Remove(childNode);
}
}
//in case of lazy loading, the tree might contain a dummy node
//(has not been expanded). However, it might be that it's now
//completely empty...
if (observed.Count == 0)
{
TreeUtil.ClearDummyChildNode(parentNode);
parentNode.IsExpanded = false;
}
}
/// <summary>
/// Handles lazy creation of child nodes if a node is being expanded
/// the first time.
/// </summary>
protected virtual void OnNodeExpanded(TreeViewItem treeNode)
{
//the node does not represent one of our bound items
//(custom root or some injected stuff)
T item = treeNode.Header as T;
if (item == null)
{
return;
}
//update the layout
string itemKey = GetItemKey(item);
currentLayout.ExpandedNodeIds.Add(itemKey);
//the tree has already been created - there is nothing more to do here
if (!IsLazyLoading)
{
//the tree has already been created - there is nothing more to do here
//however, if the node does not contain anything, don't show as expanded
if (treeNode.Items.Count == 0)
{
treeNode.IsExpanded = false;
currentLayout.ExpandedNodeIds.Remove(itemKey);
}
return;
}
//if we have a dummy node, remove it
TreeUtil.ClearDummyChildNode(treeNode);
//get the child items
ICollection <T> childItems = GetChildItems(item);
if (treeNode.Items.Count == 0)
{
foreach (T childItem in childItems)
{
//create child items with the current layout
//-> this also re-expands subitems that were
//expanded, but discarded with their ancestor
CreateItemNode(childItem, treeNode.Items, currentLayout);
}
//refresh to apply sorting
if (treeNode.Items.NeedsRefresh)
{
treeNode.Items.Refresh();
}
}
if (treeNode.Items.Count == 0)
{
//collapse again if there was no data at all
//unlikely, but the bound item's childs might have changed
treeNode.IsExpanded = false;
currentLayout.ExpandedNodeIds.Remove(itemKey);
}
}