Can I load a .NET assembly at runtime and instantiate a type knowing only the name?

c# assemblies
MegaByte picture MegaByte · Jan 21, 2009 · Viewed 198k times · Source

Is it possible to instantiate an object at runtime if I only have the DLL name and the class name, without adding a reference to the assembly in the project? The class implements a interface, so once I instantiate the class, I will then cast it to the interface.

Assembly name:

library.dll

Type name:

Company.Project.Classname

EDIT: I dont have the absolute path of the DLL, so Assembly.LoadFile won't work. The DLL might be in the application root, system32, or even loaded in the GAC.

Answer

Jeff Yates picture Jeff Yates · Jan 21, 2009

Yes. You need to use Assembly.LoadFrom to load the assembly into memory, then you can use Activator.CreateInstance to create an instance of your preferred type. You'll need to look the type up first using reflection. Here is a simple example:

Assembly assembly = Assembly.LoadFrom("MyNice.dll");

Type type = assembly.GetType("MyType");

object instanceOfMyType = Activator.CreateInstance(type);

Update

When you have the assembly file name and the type name, you can use Activator.CreateInstance(assemblyName, typeName) to ask the .NET type resolution to resolve that into a type. You could wrap that with a try/catch so that if it fails, you can perform a search of directories where you may specifically store additional assemblies that otherwise might not be searched. This would use the preceding method at that point.

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