获得Map的选择集

 ISelection selection = m_hookHelper.FocusMap.FeatureSelection;
            IEnumFeatureSetup iEnumFeatureSetup = selection as IEnumFeatureSetup;
            iEnumFeatureSetup.AllFields = true;
            IEnumFeature enumFeature = iEnumFeatureSetup as IEnumFeature;
            enumFeature.Reset();
            IFeature feature = enumFeature.Next();