C# in a Nutshell, Second Edition

Name

Activator

Synopsis

This class is used to activate objects; that is, it either creates an object or obtains a handle to an existing object. This class is generally used in a variety of specialized conditions. For example, Activator can create an object within another AppDomain and hold a handle to that object. This effectively gives a multidomain container application (such as ASP.NET) the ability to reach into another AppDomain to perform tasks within that domain (such as closing down the AppDomain in the event of a user request to shut down the application server).

Activator’s methods come in two distinct flavors: CreateInstance( ) and CreateInstanceFrom( ). These create new objects when given particular criteria (such as the type to create and the assembly from which to create it). The GetObject( ) method uses published System.Runtime.Remoting.RemotingConfiguration data to locate another object and obtain a handle to it (usually in preparation for some remote-object method invocations).

All of the methods in Activator return a System.Runtime.Remoting.ObjectHandle, not the actual object itself; this object is actually a proxy to the created/remote object. As such, programmers must call Unwrap( ) on the returned ObjectHandle to use the object. (Note that an explicit downcast is required, since the return value is declared to be a generic object.)

Figure 26-5. Value types in the ...