在ArcObject开发时，有时非常让人无语的是使用new创建对象时，报"无法将类型为Systerm._ComObject的对象强制转换为类型******"，官方知道这是个坑，早就讲得非常清楚和透彻了。
Interacting with singleton objects (ArcObjects .NET 10 SDK) (arcgis.com)
大体原因：当使用New关键字创建实例化COM对象时，默认会创建一个强类型的RCW，如果这个对象已存在，则会创建为弱类型的RCW，即System.__ComObject，而.NET Framework 无法将new的强类型RCW接口转换为单实例弱类型RCW。
错误写法：
ISpatialReferenceFactory spatialReferenceFactory = new SpatialReferenceEnvironment(); ISpatialReference spatialReference = spatialReferenceFactory.CreateGeographicCoordinateSystem(4490);
正确写法：
Type t = Type.GetTypeFromProgID("esriGeometry.SpatialReferenceEnvironment");
object obj = Activator.CreateInstance(t);
ISpatialReferenceFactory spatialReferenceFactory = obj as ISpatialReferenceFactory;
ISpatialReference spatialReference = spatialReferenceFactory.CreateGeographicCoordinateSystem(4490);
那么，不禁要问了，ArcObject中哪些对象是单实例呢？下面根据官方的文档整理了一下：
|
类 |
ProgID |
备注 |
|
AccessWorkspaceFactory |
esriDataSourcesGDB.AccessWorkspaceFactory |
常用 |
|
ActionEnvironment* |
esriTrackingAnalyst.ActionEnvironment |
|
|
AGAnimationUtils |
esriAnimation.AGAnimationUtils |
|
|
AGSServerConnectionFactory |
esriGISClient.AGSServerConnectionFactory |
|
|
AMSWorkspaceFactory |
esriTrackingAnalyst.AMSWorkspaceFactory |
|
|
AnimationControlsDialog |
esriAnimationUI.AnimationControlsDialog |
仅Desktop |
|
AnimationCreateKeyframeDialog |
esriAnimationUI.AnimationCreateKeyframeDialog |
仅Desktop |
|
AnimationFromPathDialog |
esriAnimationUI.AnimationFromPathDialog |
仅Desktop |
|
AnimationLayerGroupDialog |
esriAnimationUI.AnimationLayerGroupDialog |
仅Desktop |
|
AnimationManagerDialog |
esriAnimationUI.AnimationManagerDialog |
仅Desktop |
|
AnimationTypeCamera |
esri3DAnalyst.AnimationTypeCamera |
|
|
AnimationTypeGlobeCamera |
esriGlobeCore.AnimationTypeGlobeCamera |
|
|
AnimationTypeGlobeLayer |
esriGlobeCore.AnimationTypeGlobeLayer |
|
|
AnimationTypeLayer |
esri3DAnalyst.AnimationTypeLayer |
|
|
AnimationTypeMapLayer |
esriAnimation.AnimationTypeMapLayer |
|
|
AnimationTypeMapView |
esriAnimation.AnimationTypeMapView |
|
|
AnimationTypeScene |
esri3DAnalyst.AnimationTypeScene |
|
|
AnimationTypeTimeLayer |
esriAnimation.AnimationTypeTimeLayer |
|
|
AppRef* |
esriFramework.AppRef |
仅Desktop |
|
ArcInfoWorkspaceFactory |
esriDataSourcesFile.ArcInfoWorkspaceFactory |
|
|
CadWorkspaceFactory |
esriDataSourcesFile.CadWorkspaceFactory |
常用 |
|
CieLabConversion |
esriDisplay.CieLabConversion |
|
|
CommandsEnvironment |
esriControls.CommandsEnvironment |
|
|
DddEnvironment |
esri3DAnalystUI.DddEnvironment |
仅Desktop |
|
DddServerEnvironment |
esriGeodatabase.DddServerEnvironment |
|
|
DDDToolbarEnvironment |
esri3DAnalystUI.DDDToolbarEnvironment |
仅Desktop |
|
DEGdbUtilities |
esriGeodatabase.DEGdbUtilities |
|
|
DEUtilities |
esriGeoprocessing.DEUtilities |
|
|
DummyGraduatedMarkerLayer |
esriCarto.DummyGraduatedMarkerLayer |
|
|
DummyLayer |
esriCarto.DummyLayer |
|
|
EngineEditor |
esriControls.EngineEditor |
常用，仅Engine |
|
EngineNetworkAnalystEnvironment |
esriControls.EngineNetworkAnalystEnvironment |
仅Engine |
|
EnvironmentManager |
esriSystem.EnvironmentManager |
常用 |
|
ErrorDialog |
esriSystemUtility.ErrorDialog |
仅Engine (C++) |
|
ErrorMessage |
esriSystemUtility.ErrorMessage |
仅Engine (C++) |
|
ExcelWorkspaceFactory |
esriDataSourcesOleDB.ExcelWorkspaceFactory |
常用 |
|
ExtensionManager |
esriSystem.ExtensionManager |
|
|
FileGDBWorkspaceFactory |
esriDataSourcesGDB.FileGDBWorkspaceFactory |
常用 |
|
FindDialog |
esriCatalogUI.FindDialog |
仅Desktop |
|
FormatList |
esriDataSourcesRaster.FormatList |
|
|
GeoDatabaseHelper |
esriGeodatabase.GeoDatabaseHelper |
|
|
GMxEffectsToolbarEnvironment |
esriArcGlobe.GMxEffectsToolbarEnvironment |
仅Desktop |
|
GPGlobeFunctionFactory |
esriGlobeCore.GPGlobeFunctionFactory |
|
|
GPHolder |
esriGeoprocessing.GPHolder |
|
|
GPSAUtil |
esriSpatialAnalyst.GPSAUtil |
|
|
GPServerFunctionFactory |
esriGeoprocessing.GPServerFunctionFactory |
|
|
GpsPositionDialog |
esriArcMapUI.GpsPositionDialog |
仅Desktop |
|
GPUtilities |
esriGeoprocessing.GPUtilities |
|
|
GxCatalogROT |
esriCatalogUI.GxCatalogROT |
仅Desktop |
|
GxDatabaseExtensions |
esriCatalog.GxDatabaseExtensions |
仅Desktop |
|
IdentifyDialog |
esriCartoUI.IdentifyDialog |
仅Desktop |
|
IMSWorkspaceFactory |
esriGISClient.IMSWorkspaceFactory |
|
|
InMemoryWorkspaceFactory |
esriDataSourcesGDB.InMemoryWorkspaceFactory |
|
|
LabelEnvironment |
esriCarto.LabelEnvironment |
|
|
LayerEffectsEnvironment |
esriArcMapUI.LayerEffectsEnvironment |
仅Desktop |
|
LocatorManager |
esriLocation.LocatorManager |
|
|
MemoryRelationshipClassFactory |
esriGeodatabase.MemoryRelationshipClassFactory |
|
|
MessageLogger |
esriSystem.MessageLogger |
|
|
MetadataSynchronizer |
esriGeodatabase.MetadataSynchronizer |
|
|
MonitorSettings |
esriDisplay.MonitorSettings |
|
|
MyPlaceCollection |
esriControls.MyPlaceCollection |
仅Engine |
|
NADirectionsWindowManager |
esriNetworkAnalystUI.NADirectionsWindowManager |
仅Desktop |
|
NetCDFWorkspaceFactory |
esriDataSourcesNetCDF.NetCDFWorkspaceFactory |
|
|
NetworkIdentifyDialog |
esriNetworkAnalystUI.NetworkIdentifyDialog |
仅Desktop |
|
OLEDBWorkspaceFactory |
esriDataSourcesOleDB.OLEDBWorkspaceFactory |
常用 |
|
PCCoverageWorkspaceFactory |
esriDataSourcesFile.PCCoverageWorkspaceFactory |
|
|
RasterAnalysisToolbarEnvironment |
esriSpatialAnalystUI.RasterAnalysisToolbarEnvironment |
仅Desktop |
|
RasterAttributeTableManager |
esriDataSourcesRaster.RasterAttributeTableManager |
|
|
RasterDefaultsEnv |
esriCarto.RasterDefaultsEnv |
|
|
RasterSettings |
esriSpatialAnalystUI.RasterSettings |
仅Desktop |
|
RasterStatus |
esriDataSourcesRaster.RasterStatus |
|
|
RasterWorkspaceFactory |
esriDataSourcesRaster.RasterWorkspaceFactory |
常用 |
|
RelQueryTableFactory |
esriGeodatabase.RelQueryTableFactory |
常用 |
|
SAExtension |
esriSpatialAnalystUI.SAExtension |
仅Desktop |
|
SchematicProjectMgr |
esriSchematic.SchematicProjectMgr |
|
|
SchematicWorkspaceFactory |
esriSchematic.SchematicWorkspaceFactory |
|
|
ScratchWorkspaceFactory |
esriDataSourcesGDB.ScratchWorkspaceFactory |
|
|
SDCWorkspaceFactory |
esriDataSourcesFile.SDCWorkspaceFactory |
|
|
SdeWorkspaceFactory |
esriDataSourcesGDB.SdeWorkspaceFactory |
常用 |
|
SelectionEnvironment |
esriCarto.SelectionEnvironment |
|
|
ServerStyleGallery |
esriDisplay.ServerStyleGallery |
|
|
ShapefileWorkspaceFactory |
esriDataSourcesFile.ShapefileWorkspaceFactory |
常用 |
|
SpatialReferenceEnvironment |
esriGeometry.SpatialReferenceEnvironment |
常用 |
|
StreetMapWorkspaceFactory |
esriDataSourcesFile.StreetMapWorkspaceFactory |
|
|
StyleGallery |
esriFramework.StyleGallery |
仅Desktop |
|
SxAnimationEnvironment |
esri3DAnalyst.SxAnimationEnvironment |
|
|
SxEffectsToolbarEnvironment |
esriArcScene.SxEffectsToolbarEnvironment |
仅Desktop |
|
SymbologyEnvironment |
esriDisplay.SymbologyEnvironment |
|
|
SystemHelper |
esriSystem.SystemHelper |
|
|
TAExtension |
esriTrackingAnalystUI.TAExtension |
仅Desktop |
|
TextFileWorkspaceFactory |
esriDataSourcesOleDB.TextFileWorkspaceFactory |
常用 |
|
TexturePersistenceProperties |
esriGeometry.TexturePersistenceProperties |
|
|
TinWorkspaceFactory |
esriDataSourcesFile.TinWorkspaceFactory |
常用 |
|
TMS_MarshalHelper |
esriTrackingAnalyst.TMS_MarshalHelper |
|
|
ToolboxWorkspaceFactory |
esriGeoprocessing.ToolboxWorkspaceFactory |
|
|
TrackingEnvironment |
esriTrackingAnalyst.TrackingEnvironment |
|
|
VpfWorkspaceFactory |
esriDataSourcesFile.VpfWorkspaceFactory |
|
|
WMSConnectionFactory |
esriGISClient.WMSConnectionFactory |
|
|
WorkspaceFactory |
esriGeodatabase.WorkspaceFactory |
|
|
XMLTypeMapper |
esriSystem.XMLTypeMapper |