Question

I’m trying to learn reflection in C# and need some help with my code. I’ve had trouble finding good code examples/guides, so I apologize if my code is poorly done.

Essentially I’m just trying to check out a given assembly dll for a particular method name (path and method name have been redacted).

The problem occurs on the line object lateBoundObj = asm.CreateInstance(typeName); and it reads An object reference is required for the non-static field, method, or property...

I understand this has to do with static vs non-static and creating a new Assembly or something along those lines, but need some help understanding the issue and how to fix it.

Thank you!

 public const string assemblyPath = @"<my file path>";
    Assembly asm;

    static void Main(string[] args)
    {
        //asm = new Assembly();
        Console.Read();

        MethodInfo mi;
        object result = null;
        object[] arguments = new object[] { "ABC123" };

        try
        {
            Assembly assemblyInstance = Assembly.LoadFrom(assemblyPath);
            Type[] types = assemblyInstance.GetTypes();

            foreach (Type t in types)
            {
                mi = t.GetMethod("<my method name>");

                if (mi != null)
                {
                    string typeName = t.FullName;
                    object lateBoundObj = asm.CreateInstance(typeName);
                    result = t.InvokeMember("GetWeb", BindingFlags.Public | BindingFlags.InvokeMethod | BindingFlags.Instance, null, lateBoundObj, arguments);
                    break;
                }
            }
            //set return for find method
        }
        catch (Exception ex) { }
    }

Answer 1

The problem is that you’re never assigning a value to asm, so it’s got the default value of null. Perhaps you meant to use assemblyInstance instead?

In fact, I wouldn’t use Assembly.CreateInstance or Type.FullName at all there – I’d use:

object lateBoundObj = Activator.CreateInstance(t);

Also note, you should always avoid code like this:

catch (Exception ex) { }

Always at least log the exception. Ideally, don’t catch an exception you can’t really “handle” at all.