C# 4 and .NET 4

454 ❘ ChaPTer 18 Assemblies
should be loaded. In the example, a path using the HTTP protocol is used. A directory on a local system or
a share is specified by using href=“file://C:/WroxUtils/SharedDemo.dll”.
When the is not configured and the assembly is not stored in the GAC, the runtime tries to
find an assembly through probing. The .NET runtime tries to find assemblies with either a .dll or an
.exe file extension in the application directory or in one of its subdirectories that has the same name as the
assembly searched for. If the assembly is not found here, the search continues. You can configure search
directories with the element in the section of application configuration files. This
XML configuration can also be done easily by selecting the properties of the application with the .NET
Framework Configuration tool. You can configure the directories where the probing should occur by using
the search path in the .NET Framework configuration.
The XML file produced has these entries:
The element has just a single required attribute: privatePath. This application configuration
file tells the runtime that assemblies should be searched for in the base directory of the application, followed
by the bin and the util directory. Both directories are subdirectories of the application base directory. It’s
not possible to reference a private assembly outside the application base directory or a subdirectory thereof.
An assembly outside of the application base directory must have a shared name and can be referenced using
the element, as you saw earlier.
Versioning
For private assemblies, versioning is not important because the referenced assemblies are copied with the
client. The client uses the assembly it has in its private directories.
This is, however, different for shared assemblies. This section looks at the traditional problems that can
occur with sharing. With shared components, more than one client application can use the same component.
The new version can break existing clients when updating a shared component with a newer version. You
can’t stop shipping new versions because new features will be requested and introduced with new versions
of existing components. You can try to program carefully to be backward compatible, but that’s not always
possible.
A solution to this dilemma could be an architecture that allows installation of different versions of shared
components, with clients using the version that they referenced during the build process. This solves a lot of
problems but not all of them. What happens if you detect a bug in a component that’s referenced from the
client You would like to update this component and make sure that the client uses the new version instead
of the version that was referenced during the build process.
Therefore, depending on the type in the fix of the new version, you sometimes want to use a newer version,
and you also want to use the older referenced version. The .NET architecture enables both scenarios.
In .NET, the original referenced assembly is used by default. You can redirect the reference to a different
version by using configuration files. Versioning plays a key role in the binding architecture — how the client
gets the right assembly where the components live.
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