Passing values back and forth appdomains

Question

Hello. I have the following code:

    public class AppDomainArgs : MarshalByRefObject {
        public string myString;
    }

    static AppDomainArgs ada = new AppDomainArgs() { myString = "abc" };

    static void Main(string[] args) {
        AppDomain domain = AppDomain.CreateDomain("Domain666");
        domain.DoCallBack(MyNewAppDomainMethod);
        Console.WriteLine(ada.myString);
        Console.ReadKey();
        AppDomain.Unload(domain);
    }

    static void MyNewAppDomainMethod() {
        ada.myString = "working!";
    }

I thought make this would make my ada.myString have "working!" on the main appdomain, but it doesn't. I thought that by inhering from MarshalByRefObject any changes made on the 2nd appdomain would reflect also in the original one(I thought this would be just a proxy to the real object on the main appdomain!)?

Thanks

Answer 1

The problem in your code is that you never actually pass the object over the boundary; thus you have two ada instances, one in each app-domain (the static field initializer runs on both app-domains). You will need to pass the instance over the boundary for the MarshalByRefObject magic to kick in.

For example:

using System;
class MyBoundaryObject : MarshalByRefObject {
    public void SomeMethod(AppDomainArgs ada) {
        Console.WriteLine(AppDomain.CurrentDomain.FriendlyName + "; executing");
        ada.myString = "working!";
    }
}
public class AppDomainArgs : MarshalByRefObject {
    public string myString { get; set; }
}
static class Program {
     static void Main() {
         AppDomain domain = AppDomain.CreateDomain("Domain666");
         MyBoundaryObject boundary = (MyBoundaryObject)
              domain.CreateInstanceAndUnwrap(
                 typeof(MyBoundaryObject).Assembly.FullName,
                 typeof(MyBoundaryObject).FullName);

         AppDomainArgs ada = new AppDomainArgs();
         ada.myString = "abc";
         Console.WriteLine("Before: " + ada.myString);
         boundary.SomeMethod(ada);
         Console.WriteLine("After: " + ada.myString);         
         Console.ReadKey();
         AppDomain.Unload(domain);
     }
}

Answer 2

Btw, are you sure you need MyBoundaryObject to inherit from MarshalByRefObject?

This code seems to work as expected without using it:

class MyBoundaryObject {
    public string Test(string str) {
        Console.WriteLine(AppDomain.CurrentDomain.FriendlyName);
        return str.ToUpper();
    }
}

static class Program {
    static void Main() {
        Console.WriteLine(AppDomain.CurrentDomain.FriendlyName);

        AppDomain domain = AppDomain.CreateDomain("Domain666");
        MyBoundaryObject boundary = (MyBoundaryObject)
             domain.CreateInstanceAndUnwrap(
                typeof(MyBoundaryObject).Assembly.FullName,
                typeof(MyBoundaryObject).FullName);

        Console.WriteLine(boundary.Test("hello!"));

        Console.ReadKey();
        AppDomain.Unload(domain);
    }
}