Question

I am new to programming to kindly bear me. I using c sharp, .net 4, VS 2010

I have a interface class called IHandler with method IsValidate().
I have a message like AMOUNT 50 22.4, where AMOUNT is identifier.
So format of messages can be like FLOW 12 33 23.1, again where FLOW is identifier.

Now, based on the identifier i have different classes like ( I have around 15 – 20 classes like this, as i have to validate different message formats and sequence)

1. AmountValidator

2. FlowValidator

In these classes i have implementation of IsValidate() method, as these implement IHandler class.

Now my question is, once i identify the identifier of my message like AMOUNT or FLOW i want to create instance of the class.

What is the best way to do this?( I don’t want to create 30 instances in, if else statement )

Appreciate any help.

Answer 1

You can do it like so:

IHandler handler = (IHandler)Activator.CreateInstance("assemblyname", "typename");
handler.IsValidate();

The assembly name can be found on the properties page on the project where the handlers are.

Here:

You also have to remember that everything is case-sensitive, so the typename argument can’t be AMOUNTValidator if the class is actually named AmountValidator.

EDIT: Factory sample:

public static class HandlerFactory {
    private static Object factoryLock = new Object();
    private static List<IHandler> handlers = null;

    public static IHandler Gethandler(String type) {
        if (handlers == null) {
            lock (factoryLock) {
                if (handlers == null) {
                    IEnumerable<Type> types = typeof(HandlerFactory).Assembly.GetTypes().Where(t => t.GetInterfaces().Contains(typeof(IHandler)));
                    handlers = types.Select(t => (IHandler)Activator.CreateInstance(t));
                }
            }
        }
        return handlers.Where(h => h.Type == type);
    }
}

public interface IHandler {
    String Type { get; }
    Boolean IsValid(String data);
}