Question

I am using an external DLL which has an abstract baseclass Packet and subclasses to Packet.

The subclasses are named after the number they represent, one name could be P132_RandomString. I am parsing a file containing these numbers and for each number I want to create a corresponding object. There are hundreds of different subclasses and the DLL have no factory method (at least not for my input).

The problem is I don’t know the “RandomString” part, if I did I could have used Reflection but I assume there is no way to use Reflection since I only know the beginning of the classname?

The only solution I could think of is implementing my own factory method with hundreds of case statements but this feels a bit cumbersome…

My question is: is there a nice way to do this?

Answer 1

You can use a LINQ Where clause to grab the type you want.
Consider the following program:
(This assumes you know the base class and the prefix)

class Program {
    static void Main( string[] args ) {

        string prefix = "p22";
        IEnumerable<Type> types = Assembly.LoadFrom("c:\\Sample.Assembly.dll").GetTypes();    
        Type baseClass = typeof(foo);
        Type foundType = types.Where(
            t => t.Name.StartsWith( prefix ) &&
                t.IsSubclassOf( baseClass )
                ).SingleOrDefault();
        foo myClass = (foo)Activator.CreateInstance( foundType );
                //Do Stuff with myClass 
    }
}
abstract class foo { }
class p22_notMyClass { }
class p22_myclass : foo { }
}