Create objects dynamically when knowing part of classname in C#

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?

HischT · Accepted Answer · 2012-08-01 10:15:08Z

2

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 { }
}

edited Aug 1, 2012 at 10:15

HischT

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answered Jul 31, 2012 at 18:24

James

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2 Comments

HischT Over a year ago

Thank you for your answer. I have to use Assembly.LoadFrom to load the assembly file, but apart from that foundType gets null unless I remove t.IsSubClassOf( baseClass ) which is weird... Once I remove that I get the correct type but then I can't cast to the abstract class foo "InvalidCastException".

HischT Over a year ago

Update: It now works using Assembly.LoadFrom, the reason it didn't work first was that I referenced a copy of the DLL... And I got different contexts. sigh

Ivan Manzhos · Accepted Answer · 2012-07-31 18:25:41Z

0

To load all types from assembly use Assembly.GetTypes

 var objects = new List<Object>();
 Assembly SampleAssembly;
 SampleAssembly = Assembly.LoadFrom("c:\\Sample.Assembly.dll");
 // Obtain a reference to types known to exist in assembly.
 Type[] types = SampleAssembly.GetTypes();
 foreach(Type t in types)
    if(t.Name.StartsWith("P132")
       objects.Add(Activator.CreateInstance(t));

Use Activator.CreateInstance method described here

edited Jul 31, 2012 at 18:25

answered Jul 31, 2012 at 18:17

Ivan Manzhos

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Comments

Amiram Korach · Accepted Answer · 2012-07-31 18:26:09Z

0

you can use Assembly.GetTypes() method and iterate the types and find out which class has the number in its name. Then you can use Activator.CreateInstance to get an instance.

answered Jul 31, 2012 at 18:26

Amiram Korach

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Comments

Holger Just · Accepted Answer · 2012-07-31 18:31:16Z

0

Use Assembly.GetTypes + some String.IndexOf (or other matching) on Type.FullName + Activator.CreateInstance().

edited Jul 31, 2012 at 18:31

Holger Just

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answered Jul 31, 2012 at 18:21

Alexei Levenkov

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