Programming .NET Components, 2nd Edition

Remote Object Types

If the referenced object is in the same app domain as the client, usually no proxies are involved, and the client will hold a direct reference to the object. The question is, what happens when you try to call methods on a remote object in another app domain? By default, objects are not accessible from outside their own app domains, even if the call is made from another app domain in the same process. The rationale behind this decision is that .NET must first enforce app domain isolation and security. If you intend your objects to be accessed from outside their app domains, you must allow this explicitly in your design and class definition. .NET provides two options for accessing an object across an app domain boundary: by value or by reference. Accessing an object by value means that when a client in App Domain 2 calls a method on an object in App Domain 1, the object is first copied to App Domain 2, so the client gets its own cloned copy of the object. Once a copy is transferred to the remote client, the two objects are distinct and can change state independently. Any change made to the object’s state in App Domain 2 applies only to that local copy, which is completely separate from the original object. This is often referred to as marshaling by value and is similar to the analogous behavior in COM. The second way to access a remote object is by reference. In this case, the remote clients hold only a reference to the object, in the form of a proxy. Access ...