为什么查询的时候只能获取FID字段

Note, only the shape field is guaranteed with the selection. This is the default and exists for performance reasons. The IMap::FeatureSelection property is typically used to draw the map selection, not access feature attributes. This is particularly noticeable with shapefiles and coverage but also in geodatabases if the selection is large enough. Use IEnumFeatureSetup::AllFields to set a flag indicating all fields be returned with the selection. If you want to loop through the map selection to perform an operation, it is typically best to access each layer's selection rather than the entire map's selection.