You can redirect compile-time binding references to. NET Framework assemblies, third-party assemblies, or your own app's assemblies. You can redirect your app to use a different version of an assembly in a number of ways: through publisher policy, through an app configuration file; or through the machine configuration file. This article discusses how assembly binding works in the. NET Framework and how it can be configured. Assembly unification and default binding Bindings to. NET Framework assemblies are sometimes redirected through a process called assembly unification. The. NET Framework consists of a version of the common language runtime and about two dozen. NET Framework assemblies that make up the type library. These. NET Framework assemblies are treated by the runtime as a single unit. By default, when an app is launched, all references to types in code run by the runtime are directed to. NET Framework assemblies that have the same version number as the runtime that is loaded in a process. The redirections that occur with this model are the default behavior for the runtime. For example, if your app references types in the System. XML namespace and was built by using the. NET Framework 4.5, it contains static references to the System. XML assembly that ships with runtime version 4.5. If you want to redirect the binding reference to point to the System. XML assembly that ship with the. NET Framework 4, you can put redirect information in the app configuration file. A binding redirection in a configuration file for a unified. NET Framework assembly cancels the unification for that assembly. In addition, you may want to manually redirect assembly binding for third-party assemblies if there are multiple versions available. Redirecting assembly versions by using publisher policy Vendors of assemblies can direct apps to a newer version of an assembly by including a.
The process of locating and binding to an assembly begins when the runtime attempts to resolve a reference to another assembly. This reference can be either static or dynamic. The compiler records static references in the assembly manifest's metadata at build time. Dynamic references are constructed on the fly as a result of calling various methods, such as System. Reflection. Assembly. Load. The preferred way to reference an assembly is to use a full reference, including the assembly name, version, culture, and public key token (if one exists). The runtime uses this information to locate the assembly, following the steps described later in this section. The runtime uses the same resolution process regardless of whether the reference is for a static or dynamic assembly. You can also make a dynamic reference to an assembly by providing the calling method with only partial information about the assembly, such as specifying only the assembly name. In this case, only the application directory is searched for the assembly, and no other checking occurs. You make a partial reference using any of the various methods for loading assemblies such as System. Reflection. Assembly. Load or System. App Domain. Load. Finally, you can make a dynamic reference using a method such as System. Reflection. Assembly. Load and provide only partial information; you then qualify the reference using the element in the application configuration file. This element allows you to provide the full reference information (name, version, culture and, if applicable, the public key token) in your application configuration file instead of in your code. You would use this technique if you wanted to fully qualify a reference to an assembly outside the application directory, or if you wanted to reference an assembly in the global assembly cache but you wanted the convenience of specifying the full.
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