编辑时snapping的添加

 注意需要在编辑模式下进行snapping的添加（也即先需要使用IEngineEditor进入编辑状态）：

 

IMapControl3 mMap = (IMapControl3)((IToolbarControl)toolHook).Buddy;
            IEngineEditor m_engineEditor = new EngineEditorClass();
            if (m_engineEditor.EditState == esriEngineEditState.esriEngineStateNotEditing)
            {
                //Start editing the workspace of the first feature layer found.       
                ILayer currentLayer = mMap.get_Layer(0);
                if (currentLayer is IFeatureLayer)
                {
                    IFeatureLayer featureLayer = currentLayer as IFeatureLayer;
                    IDataset dataset = featureLayer.FeatureClass as IDataset;
                    IWorkspace workspace = dataset.Workspace;
                    m_engineEditor.StartEditing(workspace, mMap.Map);
                    ((IEngineEditLayers)m_engineEditor).SetTargetLayer(featureLayer, 0);
                }
                //snapping
                if (mMap.LayerCount != 0)
                {
                    IEngineEditor editor = new EngineEditorClass();
                    IEngineEditLayers editLayers = editor as IEngineEditLayers;
                    IEngineSnapEnvironment snapEnvironment = editor as IEngineSnapEnvironment;

                    IEngineFeatureSnapAgent featureSnapAgent = new EngineFeatureSnap();
                    featureSnapAgent.FeatureClass = ((IFeatureLayer)mMap.get_Layer(0)).FeatureClass; ;
                    featureSnapAgent.HitType = esriGeometryHitPartType.esriGeometryPartVertex | esriGeometryHitPartType.esriGeometryPartBoundary | esriGeometryHitPartType.esriGeometryPartEndpoint;
                    snapEnvironment.AddSnapAgent(featureSnapAgent);                   
                }

          }