Question

I have a dll written by someone else and that has many flaws. Let’s assume there is only one class defined in this DLL. I need to import this DLL and create an instance of this class.
The DLL code might be the following :

   [Serializable()]
    public class makeExceptionClass
    {
        public bool isStringNormalized(string aString)
        {
            // A null check should be performed
            return aString.IsNormalized();
        }
    }

I wrote a small program to check whether or not my program can still run even if the dll crashes. The program is just a proof of concept. It takes two arguments, the first is used to load directly the DLL from an assembly and the second is used to provoke a crash.
The code of the program is the following :

class Program
{
    [PermissionSetAttribute(SecurityAction.Demand, Name = "FullTrust")]
    static void Main(string[] args)
    {
        string typeOfLoading = args[0];
        string crash = args[1];

        // Load the DLL
        if (typeOfLoading.Equals("direct") == true)
        {
            Console.WriteLine("Loading directly a DLL");
            Assembly anAssembly = Assembly.Load("unloadableDLL");    // Directly load the DLL
            unloadableDLL.makeExceptionClass anObject = (unloadableDLL.makeExceptionClass)anAssembly.CreateInstance("unloadableDLL.makeExceptionClass");

            if (crash.Equals("crash") == true)
            {
                bool test = anObject.isStringNormalized(null);
            }
            else
            {
                bool test = anObject.isStringNormalized("test");
            }
        }
        else if (typeOfLoading.Equals("indirect") == true)
        {
            Console.WriteLine("Loading indirectly a DLL");
            AppDomain anAppDomain = AppDomain.CreateDomain("RemoteLoaderDomain");   // Assume it does not fail;
            Type t = typeof(unloadableDLL.makeExceptionClass);
            unloadableDLL.makeExceptionClass anObject = (unloadableDLL.makeExceptionClass)anAppDomain.CreateInstanceAndUnwrap("unloadableDLL", t.FullName);

            if (crash.Equals("crash") == true)
            {
                bool test = anObject.isStringNormalized(null);
            }
            else
            {
                bool test = anObject.isStringNormalized("test");
            }
            Console.WriteLine("Unloading the domain");
            AppDomain.Unload(anAppDomain);                
        }
        else
        {
            // don't care
        }

        // terminate
        Console.WriteLine("Press any key to exit");
        Console.ReadKey();
    }
}

The problem is that my program crashes regardless if the dll is loaded directly or into an AppDomain.
I am completely new to C# (I started this morning) but I have a C++ background.

Answer 1

Add try / catch around your call:

  try
  {
    if (crash.Equals("crash") == true)
    {
      bool test = anObject.isStringNormalized(null);
    }
    else
    {
      bool test = anObject.isStringNormalized("test");
    }
  } catch (Exception ex) {
    Console.WriteLine("exception in dll call: "+ex);
  }