C# 4 and .NET 4

Using a .neT Component from a CoM Client ❘ 717
aTTribuTe
InterfaceType
ClassInterface
DispId
In Out
Optional
desCriPTion
This attribute, if set to a ComInterfaceType enumeration value, enables
you to modify the default dual interface type that is created for .NET interfaces.
ComInterfaceType has the values InterfaceIsDual, InterfaceIsIDispatch,
and InterfaceIsIUnknown. If you want to apply a custom interface type to a
.NET interface, set the attribute like this: InterfaceType(ComInterfaceType
.InterfaceIsIUnknown).
This attribute enables you to modify the default dispatch interface that is created
for a class. ClassInterface accepts an argument of a ClassInterfaceType
enumeration. The possible values are AutoDispatch, AutoDual, and None. In the
previous example, you have seen that the default is AutoDispatch, because a dispatch
interface is created. If the class should only be accessible by the defined interfaces,
apply the attribute ClassInterface(ClassInterfaceType.None) to the class.
This attribute can be used with dual and dispatch interfaces to define the DispId of
methods and properties.
COM allows the specification of attributes for parameter types if the parameter
should be sent to the component In, from the component to the client Out, or in both
directions In, Out.
Parameters of COM methods may be optional. Parameters that should be optional can
be marked with the Optional attribute.
Now, you can change the C# code to specify a dual interface type for the IWelcome interface and a custom
interface type for the IMath interface. With the class DotnetComponent, the attribute ClassInterface
with the argument ClassInterfaceType.None specifies that no separate COM interface will be generated.
The attributes ProgId and Guid specify a ProgID and a GUID:
[InterfaceType(ComInterfaceType.InterfaceIsDual)]
[ComVisible(true)]
public interface IWelcome
{
[DispId(60040)]
string Greeting(string name);
}
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
[ComVisible(true)]
public interface IMath
{
int Add(int val1, int val2);
int Sub(int val1, int val2);
}
[ClassInterface(ClassInterfaceType.None)]
[ProgId("Wrox.DotnetComponent")]
[Guid("77839717-40DD-4876-8297-35B98A8402C7")]
[ComVisible(true)]
public class DotnetComponent: IWelcome, IMath
{
public DotnetComponent()
{
}
code snippet DotnetServer/DotnetServer.cs
Rebuilding the class library and the type library changes the interface definition. You can verify this with
OleView.exe. IWelcome is now a dual interface, IMath a custom interface that derives from IUnknown
instead of IDispatch, and the coclass section no longer has a _DotnetComponent interface.
www.it-ebooks.info