Question

when i try to run the code below, I am getting

“Value cannot be null. Parameter name: type”

error at runtime.

How to handle this exception and why my objectName is null here? I am expecting objectName to hold the value of local user account on my computer.

namespace Users
{
    class EnableDisableUsers
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Enter user account to be enabled or disabled");
            var user = Console.ReadLine();
            Console.WriteLine("Enter E to enable and D to disable the user account");
            string enableStr = Console.ReadLine();
            bool enable;
            var computer = ".";

            if (enableStr.Equals("E") || enableStr.Equals("e"))
            {
                enable = true;

                var objectName = "WinNT://" + computer + "/" + user + ",user"; 
                dynamic objUser = Activator.CreateInstance(Type.GetTypeFromProgID(objectName));
                objUser.AccountDisabled = false;
                objUser.SetInfo();
                Console.WriteLine(user + " Enabled = " + result.ToString());
                Console.ReadLine();
            }
            else if (enableStr.Equals("D") || enableStr.Equals("d"))
            {
                enable = false; 
                var objectName = "WinNT://" + computer + "/" + user + ",user";
                dynamic objUser = Activator.CreateInstance(Type.GetTypeFromProgID(objectName));
                objUser.AccountDisabled = true;
                objUser.SetInfo();
                Console.WriteLine(user + " Enabled = " + result.ToString());
                Console.ReadLine();    
            }
            else
            {
                Console.WriteLine("Operation for " + user + " failed ");
            }
        }
    }
}

Any help will be useful.

Answer 1

How to handle this exception and why my objectName is null here?

objectName is not going to be null. The more likely scenario is that Type.GetTypeFromProgID(objectName) is returning null, because that prog-id doesn’t exist, or the account doesn’t have access.

Check what Type.GetTypeFromProgID(objectName) returns, and act accordingly. Make sure it is actually a prog-id, and that you are using that API correctly. For example:

var type = Type.GetTypeFromProgID(objectName);
if(type == null) throw new InvalidOperationException(
    "Invalid prog-id: " + objectName);
dynamic objUser = Activator.CreateInstance(type);

---

Edit: Note that Activator.CreateInstance etc is not the same as VBScript’s GetObject. To access that, reference Microsoft.VisualBasic.dll, and use:

dynamic obj = Microsoft.VisualBasic.Interaction.GetObject(objectName);