ArcGIS Engine Developer Guide

INTERFACES AND MEMBERS
Interfaces are the access points for development with COM objects. There are
inbound interfaces, which expose the properties and methods of a class, and
outbound interfaces, which allow the class to interact with other classes.
A detailed discussion of COM and the
IUnknown interface can be found in the
Microsoft Component Object Model section of
Chapter 4, ‘Developer environments’.
IGeometry
IClone
ISupportErrorInfo
IPoint
Geometry
IGeometry : IUnknown
Properties
Methods
Point
IPoint : IGeometry
Properties
Methods
IGeometry inherits from IUknown and, in turn,
IPoint inherits from IGeometry
Inbound interface
Outbound interface
CoClass
Interface:Inherited interface
Properties
Methods
INTERFACE INHERITANCE
Since interfaces in ArcObjects are COM interfaces, they all inherit from
IUnknown, the basis for COM itself. Additionally, as illustrated in the diagrams,
some interfaces inherit from other ArcObjects interfaces. If one interface is
inherited by another interface, then the members of the initial interface are also
members of the inheriting interface. For example, since IPoint inherits from
IGeometry, the members of the IGeometry interface are also members of the IPoint
interface. This inheritance allows you to access the IPoint interface and use the
members of IGeometry directly, without needing to query interface to the
IGeometry interface.
Interface inheritance is used extensively to, in effect, add functionality to existing
interfaces. Although the rules of COM dictate that an interface signature, once
deployed, can’t change, a new interface can be created that inherits from the
original interface. For example, the IEditor2 interface extends the IEditor interface
with additional members.
INBOUND INTERFACES
Some inbound interfaces are shown on the diagrams with special notations that
provide information in addition to the usual list of members.
esriSystemName
The Name abstract class and the interface it
implements
IGxView
(optional) esri-
Catalog.IGx-
CatalogEvents
(optional) esri-
Catalog.IGx-
SelectionEvents
(optional) IGx-
ViewPrint
Name
GxView
The GxView class includes a number of
interfaces that implemented optionally.
Interfaces defined in other libraries
If the interface name is prefixed with a library name, such as esriSystem.IName,
then the interface is inherited from a library other than the one implementing it.
The library name reflects the library in which the interface is defined. In the
column at left, the Name abstract class, an object in the GeoDatabase library, is
shown. As shown by the library name prefix, the interface implemented by Name
is actually defined in the System library.
Optional interfaces
Some interfaces can be inherited optionally by other classes. For example, abstract
classes can have optional interfaces that may be included or excluded from
its subclasses. These are designated by the prefix (Optional). If you are creating
your own GxView class, you don’t need to implement the IGxViewPrint interface
to be a GxView class; however, you do need to implement the IGxView interface.
As a developer, if you intend to utilize an optional interface, you must verify that
the interface was implemented by the object with which you are working. Attempts
to access an optional interface that is not implemented will produce the
446 • ArcGIS Engine Developer Guide