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C# plugin system

Started by adam17 Apr 17, 2010 at 9:19 PM 5 replies 2.5k views

Original Post

Apr 17, 2010 at 9:19 PM

im trying to build a simple plugin system, but im having some issues. i have an abstract class that all plugin classes need to inherit from. once a plugin is built it will be put into a directory for the program to pull from. i can search the directory from the program to find the dlls and i can load their assembly. the problem that i am having is that i cannot figure out how to create an instance of that plugin class. its very easy when you know the name of the class, but how do you do it when you dont know the name of the class? thanks -adam

chlerub

Apr 17, 2010 at 9:34 PM

Load the assembly, iterate the types and find the ones that inherit your base class. Then just use activator to create an instance.

lpcstr

Apr 17, 2010 at 10:10 PM

Not to keep your from rolling your own, but are you aware of http://www.csscript.net/ ?

Telastyn

Apr 17, 2010 at 10:29 PM

There's also the Managed Extensibility Framework that is semi-official on codeplex. You put attributes on the classes you're using as a plugin, and then use the framework to search for classes with the particular metadata you want.

adam17

Apr 18, 2010 at 8:11 AM

i appreciate the help you have provided me so far. im still having a bit of a problem though.

here are my base classes, and the derived classes:

public class CommonBase    {        public virtual void DoStuff()        {            Console.WriteLine("BaseClass - DoStuff()");        }    }    public class BaseClass : CommonBase    {        public override void DoStuff()        {            Console.WriteLine("CommonBase - DoStuff()");        }    }public class Class2 : CommonBase    {        public override void DoStuff()        {            Console.WriteLine("Class2");        }    }public class Class1 : BaseClass    {        public override void DoStuff()        {            Console.WriteLine("Class1");        }    }

here is my experiment code that loads the dlls:

string currentDirectory = Directory.GetCurrentDirectory();string[] libraries = Directory.GetFiles(currentDirectory, "*.dll");CommonBase baseClass;Console.WriteLine("CurrentDirectory: " + currentDirectory);foreach (string s in libraries){     Console.WriteLine(s);     Assembly a = Assembly.LoadFile(s);     Type[] types = a.GetTypes();     foreach (Type t in types)     {          if (t.BaseType == typeof(CommonBase))          {               Console.WriteLine(t.FullName + " is a type of CommonBase");               baseClass = (CommonBase)a.CreateInstance("CommonBase");               baseClass.DoStuff();      // crashes here because baseClass is null          }          Console.WriteLine();     }}

am i doing something wrong to cause the crashing?

thanks
-Adam

chlerub

Apr 18, 2010 at 8:23 AM

You pass "CommonBase" string instead of the actual type you want to instantiate.
Pass the type you found (t), not a string.

adam17

Apr 18, 2010 at 8:40 AM

Quote:
Original post by chlerub
You pass "CommonBase" string instead of the actual type you want to instantiate.
Pass the type you found (t), not a string.

WOOHOO!!! thanks for the help! that got it working!

thanks
-Adam

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