ArcGIS Engine Developer Guide

.NET APPLICATION PROGRAMMING INTERFACE
• Include HRESULTs in user-defined exceptions.
• Supply GUIDs for types that require them.
• Expect inheritance differences.
For more information, review ‘Interoperating with Unmanaged Code’ in the
MSDN help collection.
Performance considerations
COM Interop clearly adds a new layer of overhead to applications, but the overall
cost of interoperating between COM and .NET is small and often unnoticeable.
However, the cost of creating wrappers and having them marshall between
environments does add up; if you suspect COM Interop is the bottleneck in your
application’s performance, try creating a COM worker class that wraps all the
chatty COM calls into one function that managed code can invoke. This improves
performance by limiting the marshalling between the two environments.
COM to .NET type conversion
Generally speaking, the type library importer imports types with the same name
they originally had in COM. All imported types are additionally added to a
namespace that has the following naming convention: ESRI.ArcGIS plus the
name of the library. For example, the namespace for the Geometry library is
ESRI.ArcGIS.Geometry. All types are identified by their complete namespace and
type name.
Classes, interfaces, and members
All COM coclasses are converted to managed classes; the managed classes have
the same name as the original with ‘Class’ appended. For example, the Point
coclass is PointClass.
All classes also have an interface with the same name as the coclass that corresponds
to the default interface for the coclass. For example, the PointClass has a
Point interface. The type library importer adds this interface so clients can register
event sinks.
The .NET classes also have class members that .NET supports, but COM does
not. Each member of each interface the class implements is added as a class
member. Any property or method a class implements can be accessed directly
from the class rather than having to cast to a specific interface. Since interface
member names are not unique, name conflicts are resolved by adding the interface
name and an underscore as a prefix to the name of each conflicting member.
When member names conflict, the first interface listed with the coclass remains
unchanged.
Properties in C# that have by-reference or multiple parameters are not supported
with the regular property syntax. In these cases, it is necessary to use the accessor
methods instead. The following code excerpt shows an example.
ILayer layer = mapControl.get_Layer(0);
MessageBox.Show(layer.Name);
Chapter 4 • Developer environments • 147