1、地图级别的选择 IMap.Featureselection
2、图层级别的选择 IFeatureselection.SelectionSet (Featurelayer支持三个重要的接口IFeatureLayer\IGeoFeaturelayer\IFeatureselection，各有不用用处)
public sub getlayerselection()
dim pmxdoc as imxdocument
dim pfsel as ifeatuerselection
dim pselset as iselectionset
set pmxdoc=thisdocument
set pfsel=pmxdoc.selectedlayer
set pselset=pfsel.selectionset
msgbox "pselset.count"
end sub