C# 4 and .NET 4

Configuring .neT applications ❘ 453
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from the machine configuration. The application configuration file should be the preferred place for
application-specific settings so that the machine configuration file stays smaller and more manageable.
A machine configuration file is located in %runtime_install_path%\config\Machine.config.
Publisher policy files can be used by a component creator to specify that a shared assembly is
compatible with older versions. If a new assembly version just fixes a bug of a shared component,
it is not necessary to put application configuration files in every application directory that uses this
component; the publisher can mark it as compatible by adding a publisher policy file instead. In case
the component doesn’t work with all applications, it is possible to override the publisher policy setting
in an application configuration file. In contrast to the other configuration files, publisher policy files
are stored in the GAC.
How are these configuration files used How a client finds an assembly (also called binding) depends on
whether the assembly is private or shared. Private assemblies must be in the directory of the application or
in a subdirectory thereof. A process called probing is used to find such an assembly. If the assembly doesn’t
have a strong name, the version number is not used with probing.
Shared assemblies can be installed in the GAC or placed in a directory, on a network share, or on a web site.
You specify such a directory with the configuration of the codeBase shortly. The public key, version, and
culture are all important aspects when binding to a shared assembly. The reference of the required assembly
is recorded in the manifest of the client assembly, including the name, the version, and the public key token.
All configuration files are checked to apply the correct version policy. The GAC and code bases specified
in the configuration files are checked, followed by the application directories, and probing rules are then
applied.
binding to assemblies
You’ve already seen how to install a shared assembly to the GAC. Instead of installing a shared assembly to
the GAC, you can configure a specific shared directory by using configuration files. This feature can be used
if you want to make the shared components available on a server. Another possible scenario arises if you
want to share an assembly between your applications, but you don’t want to make it publicly available in the
GAC, so you put it into a shared directory instead.
There are two ways to find the correct directory for an assembly: the codeBase element in an XML
configuration file, or through probing. The codeBase configuration is available only for shared assemblies,
and probing is done for private assemblies.
The can be configured with an application configuration file. The following application
configuration file redirects the search for the assembly SharedDemo to load it from the network:
The element has the attributes version and href. With version, the original referenced
version of the assembly must be specified. With href, you can define the directory from which the assembly
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