// Get fc for selection on usa.
IResultSetFeatureCollection fc = session1.Selections.DefaultSelection[tableUsa];
int nCount=0;
if (fc != null)
{
nCount = fc.Count;
}
TextBox1.Text=nCount.ToString();
string aaa="";
foreach(Feature f in fc)//f为所有选中的图元
{
aaa+=f.Key.ToString()+",";