ArcGIS Engine Developer Guide

PUTTING IT TOGETHER—AN EXAMPLE
IWorkspaceName
(optional) IDatabaseCompact
IWorkspaceName2
Workspace-
Name
esriSystemName
The Name abstract class, WorkspaceName and
Tablename coclasses, and FeatureClass objects
and their relationships
In this example, the abstract
class Name implements the
IName interface; its inheritance
Name
relationship to all other name
objects indicates that they each
implement the IName interface
IFeatureClassName
as well. Although neither the
ITopologyClassName FeatureClass-
Name
FeatureClassName nor
*
WorkspaceName coclass shows
the IName interface in the
IFeatureClass
*
FeatureClass
diagrams, you know it is there
because of this inheritance. The
Open() method on the IName
interface is used to instantiate
the FeatureClass object. This
usage guarantees that the new FeatureClass object is properly created and includes
all necessary information.
The case below illustrates its importance clearly: opening a shapefile dataset to
extract a feature class is not as simple as just reading the database records.
Dim pwrkspc As IWorkspaceName
Set pwrkspc = New WorkspaceName
pwrkspc.PathName = "D:\data\canada"
pwrkspc.WorkspaceFactoryProgID = _
"esriDataSourcesFile.shapefileworkspacefactory.1"
'***************************************************
Dim pdatasetname As IDatasetName
Set pdatasetname = New FeatureClassName
pdatasetname.Name = "Canada.dbf"
Set pdatasetname.WorkspaceName = pwrkspc
Dim pname As IName
Set pname = pdatasetname
Dim pfeatclass As IFeatureClass
Set pfeatclass = pname.Open
''Check FeatureType property to ensure you have a featureclass object
MsgBox pfeatclass.FeatureType
An association is shown in the code above where the WorkspaceName object was
set to the WorkspaceName property of the FeatureClassName object. As noted
earlier, for simplicity’s sake, many of the associations in ArcObjects aren’t drawn
on the diagrams. In fact, this association between the WorkspaceName and
FeatureClassName classes isn’t shown on the GeoDatabase library object model
diagram; however, it can be seen in the IName interface detail for the
WorkspaceName property since the symbol used is a Property Put by Reference.
Since the WorkspaceName class is being held as a reference and not in a composition
relationship, the object’s lifespan will not be controlled by the
FeatureClassName object. If you were to use the code below to set the
FeatureClassName object to nothing, the WorkspaceName class would still exist.
Set pfeatclass = Nothing
If Not pwrkspc Is Nothing Then
MsgBox "Object still exists"
End If
Appendix A • Reading the object model diagrams • 449