Instantiate a class from its textual name

Question

Don't ask me why but I need to do the following:

string ClassName = "SomeClassName";  
object o = MagicallyCreateInstance("SomeClassName");

I want to know how many ways there are to do this is and which approach to use in which scenario.

Examples:

• Activator.CreateInstance
• Assembly.GetExecutingAssembly.CreateInstance("")
• Any other suggestions would be appreciated

This question is not meant to be an open ended discussion because I am sure there are only so many ways this can be achieved.

Solution 1

Here's what the method may look like:

private static object MagicallyCreateInstance(string className)
{
    var assembly = Assembly.GetExecutingAssembly();

    var type = assembly.GetTypes()
        .First(t => t.Name == className);

    return Activator.CreateInstance(type);
}

The code above assumes that:

• you are looking for a class that is in the currently executing assembly (this can be adjusted - just change assembly to whatever you need)
• there is exactly one class with the name you are looking for in that assembly
• the class has a default constructor

Update:

Here's how to get all the classes that derive from a given class (and are defined in the same assembly):

private static IEnumerable<Type> GetDerivedTypesFor(Type baseType)
{
    var assembly = Assembly.GetExecutingAssembly();

    return assembly.GetTypes()
        .Where(baseType.IsAssignableFrom)
        .Where(t => baseType != t);
}

Solution 2

Activator.CreateInstance(Type.GetType("SomeNamespace.SomeClassName"));

or

Activator.CreateInstance(null, "SomeNamespace.SomeClassName").Unwrap();

There are also overloads where you can specify constructor arguments.

Comments

[Raheel Khan]

Exactly what I needed, thanks. I also need to enumerate all classes that derive this class we just created. I'm assuming assembly.GetTypes would allow that.

[Cristian Lupascu]

@RaheelKhan I have added a code sample for getting the derived classes defined in the same assembly.

[andrefadila]

After we got the class, can we call the method inside?

[Cristian Lupascu]

@andrefadila Yes. Be aware though that Activator.CreateInstance returns an object and you may need to cast it first.

[andrefadila]

Thanks for response @w0lf. So, we must cast it first. Is there any solution without cast?

[Cristian Lupascu]

You could also call the method via reflection. (This is pretty hacky)

[Cristian Lupascu]

Or you could cast the object not to its exact type, but to an interface that defines that method.

[Saurabh Shah]

What if the class I want to instantiate is not in the current assembly but lies in the same solution?