INotifyPropertyChanged does not notify UI

好吧，我有以下类定义：

    private ObservableCollection<Node> _Nodes;
    public ObservableCollection<Node> Nodes
    {
        get
        {
            return _Nodes;
        }
        set
        {
            _Nodes = value;
            OnPropertyChanged("Nodes");
        }
    }

Node类：

[Serializable]
public class Node : INotifyPropertyChanged
{        
    private string _Name;
    [XmlAttribute("Name")]
    public string Name
    {
        get
        {
            return _Name;
        }
        set
        {
            _Name = value;
            OnPropertyChanged("Name");
        }
    }

    private bool _IsChecked;
    [XmlIgnore()]
    public bool IsChecked
    {
        get
        {
            return _IsChecked;
        }
        set
        {
            _IsChecked = value;
            OnPropertyChanged("IsChecked");
        }
    }

当在CCD_ 2中时，我修改一个元素：

try
        {
            foreach (var node in AllNodes)
            {
                if (node.Children.Contains(s))
                {
                    for (int i = 0; i < node.Children.Count; i++)
                    {
                        if (node.Children[i] == s)
                        {
                            node.Children[i] = null;
                        }
                    }
                }
            }
        }
        catch (NullReferenceException)
        {
        }

UI恰好什么也不做。但再次加载文件解决了问题：）AllNodes是Node 的Observable集合

有办法做到这一点吗？