ArcGIS Engine Developer Guide

.NET APPLICATION PROGRAMMING INTERFACE
that variable can be used to access the IPoint::PutCoords method from this class
interface.
[VB.NET]
Dim thePt As ESRI.ArcGIS.Geometry.Point = New ESRI.ArcGIS.Geometry.Point()
thePt.PutCoords(10,8)
[C#]
ESRI.ArcGIS.Geometry.Point thePt = newESRI.ArcGIS.Geometry.Point();
thePt.PutCoords(10,8);
The inherited interface of a class interface is not guaranteed to remain the same
between versions of ArcGIS and, therefore, it is recommended that you avoid
using the above syntax.
You can view these types in the VB .NET Object Browser. Notice that using
Visual Basic .NET, PointClass is not shown by default but can be made visible by
selecting the Show Hidden Members option. In the C# Object Browser, you can
see more clearly the class interface Point and its inherited interface IPoint and the
class PointClass.
.NET PROGRAMMING TECHNIQUES AND CONSIDERATIONS
This section contains several programming tips and techniques to help developers
who are moving to .NET.
Casting between interfaces (QueryInterface)
.NET uses casting to jump from one interface to another interface on the same
class. In COM this is called QueryInterface. VB.NET and C# cast differently.
VB.NET
There are two types of casts, implicit and explicit. Implicit casts require no
additional syntax, whereas explicit casts require cast operators.
geometry = point
' Implicit cast
geometry = CType(point, IGeometry) ' Explicit cast
When casting between interfaces, it’s perfectly acceptable to use implicit casts
because there is no chance of data loss as there is when casting between numeric
types. However, when casts fail, an exception (System.InvalidCastException) is
thrown; to avoid handling unnecessary exceptions, it’s best to test if the object
implements both interfaces beforehand. The recommended technique is to use the
TypeOf keyword, which is a comparison clause that tests whether an object is
derived from or implements a particular type, such as an interface. The example
below performs an implicit conversion from an IPoint to an IGeometry only if at
runtime it is determined that the Point class implements IGeometry.
Dim point As New PointClass
Dim geometry As IGeometry
If (TypeOf point Is IGeometry) Then
geometry = point
End If
If you prefer using the Option Strict On statement to restrict implicit conversions,
use the CType function to make the cast explicit. The example below adds
an explicit cast to the code sample above.
Dim point As New PointClass
150 • ArcGIS Engine Developer Guide