ArcEngine GroupLayer监听图层改变

最近项目中需要用到在TOC监听图层的变化，从而针对添加的不同图层进行不同的操作。但是当TOC中添加图层组时，无法监听到图层组中添加图层的动作。也就无法获取到向图层组中添加的图层。
在开发手册中也没有找到相应的事件接口来实现。于是就动手自己写了一个事件监听。
实现的思路是，自己构建事件接口，然后构建一个GroupLayer的子类来实现这个接口。
具体看代码：

///////////////////////////////
/////// 事件接口的代码
    // 构建图层组图层增加的委托
    public delegate void IGroupLayerEvents_ItemAddedEventHandler(object Item);
	// 构建图层组图层移除的委托
    public delegate void IGroupLayerEvents_ItemDeletedEventHandler(object Item);
    
	// 构建图层组事件接口
    public interface IGroupLayerEvents
    {
	    // 增加项事件
        event IGroupLayerEvents_ItemAddedEventHandler ItemAdded;
		// 移除项事件
        event IGroupLayerEvents_ItemDeletedEventHandler ItemDeleted;
    }

////////////
///构建GroupLayerClass的子类
    // 构建GrouplayerClassEx类继承Esri的GroupLayer并实现自定义的IG肉pLayerEvents接口
    public class GroupLayerClassEx:GroupLayerClass,IGroupLayerEvents
    {
        #region IGroupLayerEvents 成员
        public event IGroupLayerEvents_ItemAddedEventHandler ItemAdded;
        public event IGroupLayerEvents_ItemDeletedEventHandler ItemDeleted;
        #endregion
		
		// 重写添加的方法
		public override void Add(ILayer layer)
        {
            base.Add(layer);
			// 实现事件
            if (ItemAdded != null)
            {
                ItemAdded(layer);
            }
        }
		
		// 重写清除的方法
		public override void Clear()
        {
		    // 遍历图层实现项减少的事件
            if (ItemDeleted != null)
            {
                ICompositeLayer pCompositeLayer = this as ICompositeLayer;
                for (int i = 0; i < pCompositeLayer.Count; i++)
                {
                    ILayer pCurrentLayer = pCompositeLayer.get_Layer(i);
                    ItemDeleted(pCurrentLayer);
                }
            }
            base.Clear();
        }
		
		// 重写删除的方法
		public override void Delete(ILayer Layer)
        {
            base.Delete(Layer);
            if (ItemDeleted != null)
            {
                ItemDeleted(Layer);
            }
        }
		···
		其他IGroupLayer接口实现的方法和属性都要override一遍。
		···
    }

在地图控件事件中进行监听

 private void axMapControl1_OnMapReplaced(object sender, IMapControlEvents2_OnMapReplacedEvent e)
 {
    AxMapControl pAxMapControl = sender as AxMapControl;

    // 注册事件
    mEvent = pAxMapControl.ActiveView.FocusMap as IActiveViewEvents_Event;
    mEvent.ItemAdded += new IActiveViewEvents_ItemAddedEventHandler(Event_ItemAdded);
    mEvent.ItemDeleted += new IActiveViewEvents_ItemDeletedEventHandler(Event_ItemDeleted); 
 }
  private void Event_ItemAdded(object Item)
  {
      if (Item is IGroupLayer)
      {
        IGroupLayerEvents pIGroupLayerEvents = Item as IGroupLayerEvents;
        if (pIGroupLayerEvents != null)
        {
          pIGroupLayerEvents.ItemAdded += new IGroupLayerEvents_ItemAddedEventHandler(Event_ItemAdded);
          pIGroupLayerEvents.ItemDeleted += new IGroupLayerEvents_ItemDeletedEventHandler(Event_ItemDeleted);
         }
     }
  }