Loading DLLs at runtime in C#

Question

I am trying to figure out how you could go about importing and using a .dll at runtime inside a C# application. Using Assembly.LoadFile() I have managed to get my program to load the dll (this part is definitely working as I am able to get the name of the class with ToString()), however I am unable to use the 'Output' method from inside my console application. I am compiling the .dll then moving it into my console's project. Is there an extra step between CreateInstance and then being able to use the methods?

This is the class in my DLL:

namespace DLL {     using System;      public class Class1     {         public void Output(string s)         {             Console.WriteLine(s);         }     } } 

and here is the application I want to load the DLL

namespace ConsoleApplication1 {     using System;     using System.Reflection;      class Program     {         static void Main(string[] args)         {             var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");              foreach(Type type in DLL.GetExportedTypes())             {                 var c = Activator.CreateInstance(type);                 c.Output(@"Hello");             }              Console.ReadLine();         }     } } 

Answer 1

Members must be resolvable at compile time to be called directly from C#. Otherwise you must use reflection or dynamic objects.

Reflection

namespace ConsoleApplication1 {     using System;     using System.Reflection;      class Program     {         static void Main(string[] args)         {             var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");              foreach(Type type in DLL.GetExportedTypes())             {                 var c = Activator.CreateInstance(type);                 type.InvokeMember("Output", BindingFlags.InvokeMethod, null, c, new object[] {@"Hello"});             }              Console.ReadLine();         }     } } 

Dynamic (.NET 4.0)

namespace ConsoleApplication1 {     using System;     using System.Reflection;      class Program     {         static void Main(string[] args)         {             var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");              foreach(Type type in DLL.GetExportedTypes())             {                 dynamic c = Activator.CreateInstance(type);                 c.Output(@"Hello");             }              Console.ReadLine();         }     } } 

Answer 2

Right now, you're creating an instance of every type defined in the assembly. You only need to create a single instance of Class1 in order to call the method:

class Program {     static void Main(string[] args)     {         var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");          var theType = DLL.GetType("DLL.Class1");         var c = Activator.CreateInstance(theType);         var method = theType.GetMethod("Output");         method.Invoke(c, new object[]{@"Hello"});          Console.ReadLine();     } }