Correct Way to Load Assembly, Find Class and Call Run() Method

Question

Sample console program.

class Program {     static void Main(string[] args)     {         // ... code to build dll ... not written yet ...         Assembly assembly = Assembly.LoadFile(@"C:\dyn.dll");         // don't know what or how to cast here         // looking for a better way to do next 3 lines         IRunnable r = assembly.CreateInstance("TestRunner");         if (r == null) throw new Exception("broke");         r.Run();      } } 

I want to dynamically build an assembly (.dll), and then load the assembly, instantiate a class, and call the Run() method of that class. Should I try casting the TestRunner class to something? Not sure how the types in one assembly (dynamic code) would know about my types in my (static assembly / shell app). Is it better to just use a few lines of reflection code to call Run() on just an object? What should that code look like?

UPDATE: William Edmondson - see comment

Answer 1

Use an AppDomain

It is safer and more flexible to load the assembly into its own AppDomain first.

So instead of the answer given previously:

var asm = Assembly.LoadFile(@"C:\myDll.dll"); var type = asm.GetType("TestRunner"); var runnable = Activator.CreateInstance(type) as IRunnable; if (runnable == null) throw new Exception("broke"); runnable.Run(); 

I would suggest the following (adapted from this answer to a related question):

var domain = AppDomain.CreateDomain("NewDomainName"); var t = typeof(TypeIWantToLoad); var runnable = domain.CreateInstanceFromAndUnwrap(@"C:\myDll.dll", t.Name) as IRunnable; if (runnable == null) throw new Exception("broke"); runnable.Run(); 

Now you can unload the assembly and have different security settings.

If you want even more flexibility and power for dynamic loading and unloading of assemblies, you should look at the Managed Add-ins Framework (i.e. the System.AddIn namespace). For more information, see this article on Add-ins and Extensibility on MSDN.

Answer 2

If you do not have access to the TestRunner type information in the calling assembly (it sounds like you may not), you can call the method like this:

Assembly assembly = Assembly.LoadFile(@"C:\dyn.dll"); Type     type     = assembly.GetType("TestRunner"); var      obj      = Activator.CreateInstance(type);  // Alternately you could get the MethodInfo for the TestRunner.Run method type.InvokeMember("Run",                    BindingFlags.Default | BindingFlags.InvokeMethod,                    null,                   obj,                   null); 

If you have access to the IRunnable interface type, you can cast your instance to that (rather than the TestRunner type, which is implemented in the dynamically created or loaded assembly, right?):

  Assembly assembly  = Assembly.LoadFile(@"C:\dyn.dll");   Type     type      = assembly.GetType("TestRunner");   IRunnable runnable = Activator.CreateInstance(type) as IRunnable;   if (runnable == null) throw new Exception("broke");   runnable.Run();