private void OnNodeExpanded(TreeGridRow treeNode)
{
//处理 LazyLoading
//结点被展开后事件
//完成懒加载时的结点创建工作，并设置各结点的 Filter 属性。
object item = treeNode.DataContext;
if (item != null)
{
//布局
var itemKey = GetId(item);
_renderExpansion.Add(itemKey);
var nodeItems = treeNode.Items;
//懒加载状态下，创建结点。
if (this.IsLazyLoading)
{
TreeGridHelper.ClearDummyChildNode(treeNode);
if (nodeItems.Count == 0)
{
var childItems = this.GetChildItems(item);
treeNode.ItemsSource = childItems;
//刷新以排序
if (nodeItems.NeedsRefresh)
{
nodeItems.Refresh();
}
}
}
if (nodeItems.Count == 0)
{
//如果结点没有数据，则不需要展开它。
treeNode.IsExpanded = false;
_renderExpansion.Remove(itemKey);
}
}
}
/// <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 (or the childs that pass an active filter).<br/>
/// </summary>
/// <param name="observed">The observed collection.</param>
/// <param name="e">The event arguments that provide the
/// removed items.</param>
private void HandleRemovedChildItems(ICollection observed, NotifyCollectionChangedEventArgs e)
{
IList childs = e.OldItems;
if (childs.Count == 0)
{
return;
}
//get the node of the parent item that contains the evented childs
var parentNode = GetParentNode((object)childs[0], observed);
if (parentNode == null)
{
return;
}
foreach (object childItem in childs)
{
//check if we have a corresponding open node
//-> not necessarily the case if we're doing lazy loading
var childRow = tree.FindChildRow(childItem, parentNode);
if (childRow != null)
{
//unregister listeners
UnregisterListeners(childRow);
//remove node from UI
parentNode.Items.Remove(childRow);
}
}
//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)
{
TreeGridHelper.ClearDummyChildNode(parentNode);
parentNode.IsExpanded = false;
}
}