Hi, I have a treeview with one root node. This node has some children. The root not is a "TreeViewItemViewModel". This class contains : "ObservableCollection<TreeViewItemViewModel> Items" which are Children nodes. At beginning, the root node is not expanded and "Children" is empty. When I expand root node, I load data from DataBase in Children collection :

public override void LoadChildren()
{
this.Items.Clear();
List lstOp = DataBAse.GetAllOperations();
foreach (Operation op in lstOp)
{
this.Items.Add(new TreeViewItemViewModel(op));
}
}

If I "unexpand" and expand the root node, I reload children...

public bool IsExpanded
{
get
{
return _isExpanded;
}
set
{
if (value != this._isExpanded)
{
this._isExpanded = value;
RaisePropertyChanged("IsExpanded");

                if (this.\_isExpanded)
                {
                    this.LoadChildren();
                }
            }
        }
    }

My issue : when I call "LoadChildren", Items list is cleared but viewmodel are always in memory... Can someone help me ?