How can I create an instance when I only have the name of the class?

I'm looking for a solution to create singleton instances of classes, when only the names of the class will be available.

I've looked at Activator.CreateInstance() but this needs a recast to the original object for method invoc开发者_运维技巧ation to occur. I then went in to look at how MEF might assist, which seems to be route I want to go, but I'm not sure if this is overkill for what I'd like to achieve.

In a nutshell, I have references to web services (ASMX) with different names. These names will be exposed to a combo-box in a WinForms application when a user enters the URL to an application. From there, a couple of methods, exposed by each of the services need to be called, however, the classes will be virtual methods in the abstract class.

This sounds a lot like a plug-in framework, but the idea here is to call Microsoft specific web services in Office SharePoint Server (2007 / 2010) dynamically based on the type of foundation installed.

Hope I've given enough context.

Are you using C# 4 and .NET 4? If so, you could just use:

Type type = Type.GetType(typeName);
dynamic service = Activator.CreateInstance(type);
service.FirstCommonMethod("foo", "bar");
service.SecondCommonMethod();

Note that typeName must at least be namespace-qualified, and if the type is in an assembly other than mscorlib or the calling assembly, it should also be assembly-qualified.

The following code is slightly faster than using Activator.CreateInstance, though only barely. Mostly I'm just illustrating another way to instantiate an object by Type.

var type = Type.GetType(yourClassNamePossiblyWithLeadingNamespaces);
var expressionNew = Expression.New(type);
var typeFactory = Expression.Lambda<Func<dynamic>>(expressionNew).Compile();
var instanceOfClass = typeFactory();

EDIT: Same as Jon's answer: this needs .NET 4 and C# 4 to use dynamic.