Test if object implements interface

Question

What is the simplest way of testing if an object implements a given interface in C#? (Answer to this question in Java)

Answer 1

I had a situation where I was passing a variable to a method and wasn't sure if it was going to be an interface or an object.

The goals were:

1. If item is an interface, instantiate an object based on that interface with the interface being a parameter in the constructor call.
2. If the item is an object, return a null since the constuctor for my calls are expecting an interface and I didn't want the code to tank.

I achieved this with the following:

    if(!typeof(T).IsClass)
    {
       // If your constructor needs arguments...
       object[] args = new object[] { my_constructor_param };
       return (T)Activator.CreateInstance(typeof(T), args, null);
    }
    else
       return default(T);