I noticed that when I have a remote object, it does not do runtime type checking ('is' and 'as') correctly. The 'is' operator always returns true and 'as' never returns null. This is frustrating because my code does not behave the same with remoting as it does without. Can someone help me understand the problem and a workaround?
Hi Semorri, can you post a small snippet of code that illustrates your point? That should help make sure I'm answering the right question.
Cheers,
JJustice [MSFT]
ParentClass extends MarshalByRefObject ChildClass extends ParentClass public void method(ParentClass p) { if (p is ChildClass)..... } Code Snippet
If the reference 'p' of type ParentClass is a remote object (i.e. a proxy), then the "is" operator always evaluates to true, even if it is not really an instance of a ChildClass (or in this case, a proxy to an instance of ChildClass).
I created a little test application but I can't simulate your problem, could you give some more code on how you create the objects and what is happening in the code before you do the type checking.
Test application:
I create a new AppDomain to simulate the remoting. (It will be more readable in VS)
using System;
using System.Collections.Generic;
using System.Text;
namespace TestApp
{
class Program
{
static void Main(string[] args)
{
AppDomain remoteDomain = AppDomain.CreateDomain("MyNewdomain");
Test remoteTest = (Test)remoteDomain.CreateInstanceAndUnwrap(typeof(Test).Assembly.FullName, "TestApp.Test");
if (remoteTest is Test) { Console.WriteLine("remoteTest is a Test object"); }
else { Console.WriteLine("remoteTest is NOT a Test object"); }
if (remoteTest is DerivedTest) { Console.WriteLine("remoteTest is a DerivedTest object"); }
else { Console.WriteLine("remoteTest is NOT a DerivedTest object"); }
DerivedTest remoteDerivedTest1 = (DerivedTest)remoteDomain.CreateInstanceAndUnwrap(typeof(DerivedTest).Assembly.FullName, "TestApp.DerivedTest");
if (remoteDerivedTest1 is Test) { Console.WriteLine("remoteDerivedTest1 is a Test object"); }
else { Console.WriteLine("remoteDerivedTest1 is NOT a Test object"); }
if (remoteDerivedTest1 is DerivedTest) { Console.WriteLine("remoteDerivedTest1 is a DerivedTest object"); }
else { Console.WriteLine("remoteDerivedTest1 is NOT a DerivedTest object"); }
Test remoteDerivedTest2 = (Test)remoteDomain.CreateInstanceAndUnwrap(typeof(DerivedTest).Assembly.FullName, "TestApp.DerivedTest");
if (remoteDerivedTest2 is Test) { Console.WriteLine("remoteDerivedTest2 is a Test object"); }
else { Console.WriteLine("remoteDerivedTest2 is NOT a Test object"); }
if (remoteDerivedTest2 is DerivedTest) { Console.WriteLine("remoteDerivedTest2 is a DerivedTest object"); }
else { Console.WriteLine("remoteDerivedTest2 is NOT a DerivedTest object"); }
Console.ReadLine();
}
}
public class Test : MarshalByRefObject
{
}
public class DerivedTest : Test
{
}
}
Steven Hillaert
http://blog.hill-it.be
The code for the server side:
// set up port number and object name
System.Collections.
IDictionary properties = new System.Collections.Hashtable();properties[
"port"] = m_myDescription.PortNum.ToString();properties[
"name"] = m_myDescription.ObjectName;
// set the security level--this allows the proxy references to be put in a hashtable
BinaryServerFormatterSinkProvider serverProvider = new BinaryServerFormatterSinkProvider();serverProvider.TypeFilterLevel = System.Runtime.Serialization.Formatters.TypeFilterLevel.Full;
TcpChannel channel = new TcpChannel(properties, null, serverProvider);
// register the channel and expose the object
ChannelServices.RegisterChannel(channel, false);RemotingServices.Marshal(this, m_myDescription.ObjectName);The code on the client side:
MyClass obj = (MyClass)Activator.GetObject(typeof(MyClass), description.Url);
If you are using SAO then unfortunately your ObjRef will tell you the same information what you provided it. For instance if you look at the line you used to create the proxy, you are telling remoting that your remoting objects type if MyClass and thats what will go on the wire when you invoke a method on that proxy.
If you want to know the actual type of object hosted in case of polymorphism then you can use RemotingServices.IsTransparentProxy(obj) to determine if its a Proxy and then call the ToString() method on the remote proxy to get the actual type of the instance on the remote side (ToString will be executed on the server and hence will give you the correct type).
Something like
if (RemotingServices
.IsTransparentProxy(obj))Console.WriteLine(Type.GetType(obj.ToString()));
This assumes that you haven't overridden ToString. But worse, if you are checking at runtime if the object is of a type that implements a certain interface, ToString does not help you.
Any other work arounds?
Will WCF address this issue?
I belive this is by design. The reason behind it is that the client will not know if the conversion is valid until you try to invoke any of the operations. Effectively what it means is that any proxy can be for any type.
Thank you
A possible workaround is to expose a factory on the server side that returns a MarshalByRefObject:
Interface Factory
{
MarshalByRefObject GetObject();
}
MBRO serializes and passes back the type information.
