. NET: Messages and AOP (ii)

Using System;
Using System.Runtime.Remoting;
Using System.Runtime.Remoting.Services;
Using System.Runtime.Remoting.Activation;
Using System.Runtime.Remoting.Proxies;
Using System.Runtime.Remoting.Messaging;

/*
This procedure explains how the interception is carried out, and the relationship between the real agent and the transparent agent and interaction.
*/
Namespace Intercept_example
{
Class Class1
{
[STAThread]
static void Main (string[] args)
{
Example Exa = new Example ("Sky");
Exa.say_hello ();
}
}

Defines a real agent for implementing a specific preprocessing and reprocessing
public class Interceptproxy:realproxy
{
Private ReadOnly MarshalByRefObject Target;

Public Interceptproxy (MarshalByRefObject obj, type type): Base (Type)
{
This.target = obj;
}


public override IMessage Invoke (IMessage msg)
{
IMethodCallMessage call = (IMethodCallMessage) msg;

If the constructor is triggered, then target construction has not started
IConstructionCallMessage ctor = call as IConstructionCallMessage;
if (ctor!= null)
{
System.Console.WriteLine ("Forwarding constructor call!") ") ;

RealProxy default_proxy = Remotingservices.getrealproxy (this.target);

Default_proxy. Initializeserverobject (ctor);
MarshalByRefObject TP = (MarshalByRefObject) this. Gettransparentproxy ();

Return Enterpriseserviceshelper.createconstructionreturnmessage (CTOR,TP);

}

System.Console.WriteLine ("preprocessing ...");
System.Threading.Thread.Sleep (5000);

IMethodReturnMessage result_msg = Remotingservices.executemessage (this.target, call);

System.Console.WriteLine ("post-processing ...");
System.Threading.Thread.Sleep (5000);
System.Console.WriteLine ("End of post processing!") ") ;

return result_msg;

}
}



Defines an attribute that can associate the real agent above with the class that uses the attribute
[AttributeUsage (AttributeTargets.Class)]
public class Interceptproxyattribute:proxyattribute
{
Get Transparent Agent
public override MarshalByRefObject CreateInstance (Type servertype)
{
Uninitialized instances
MarshalByRefObject target = base. CreateInstance (ServerType);

Interceptproxy rp = new Interceptproxy (target, servertype);

Return (MarshalByRefObject) Rp. Gettransparentproxy ();
}
}

[Interceptproxy]
The public class example:contextboundobject//is placed in a particular context outside of which the transparent proxy for the object is obtained
{
private string name;
Public Example (String a)
{
THIS.name = A;
}

public void Say_hello ()
{
Console.WriteLine ("Hello!" + name);
}
}

/*
* (1) when the caller and the location are located in different contexts, the caller obtains the transparent proxy of the object being invoked. The transparent proxy packages the method call into a imessage object and passes to the Invoke method of the actual proxy.
* The default implementation of the Invoke method simply passes the imessage object to a subsequent channel, such as a stack generator, and so on. We can customize our real proxies, rewrite the Invoke method, and add preprocessing and reprocessing.
* (2) associates the real agent with the target class by proxy attributes (such as Interceptproxyattribute) (inherited from ProxyAttribute). This proxy feature overrides the ProxyAttribute CreateInstance
* CreateInstance method, in which the real agent (such as Interceptproxy) is wrapped around the target object, and the transparent proxy for the real agent is returned.
* (3) in a program, the target object's method cannot be invoked directly through a real proxy, because the real agent handles the message object (IMessage), which is based on the message world.
* (4) It is possible to join the interception (pretreatment and reprocessing) only if a reference is held with a transparent proxy.
* (5) derived from the ContextBoundObject class, we can only get its transparent proxy; The object of the class that derives from Mashalbyrefobject, we may get its transparent proxy or direct reference, depending on the adjusted party and the target
* Whether the object is in the same context; The object of a class that is not derived from these two classes, we can only get a direct reference to it.
*/



}