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

If you want to use the typecasted object after the check:
Since C# 7.0:

if (obj is IMyInterface myObj)

This is the same as

IMyInterface myObj = obj as IMyInterface;
if (myObj != null)

See .NET Docs: Pattern matching with is # Type pattern

Answer 2

I used

Assert.IsTrue(myObject is ImyInterface);

for a test in my unit test which tests that myObject is an object which has implemented my interface ImyInterface.

Answer 3

In addition to testing using the "is" operator, you can decorate your methods to make sure that variables passed to it implement a particular interface, like so:

public static void BubbleSort<T>(ref IList<T> unsorted_list) where T : IComparable
{
     //Some bubbly sorting
}

I'm not sure which version of .Net this was implemented in so it may not work in your version.

Answer 4

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);

Answer 5

Recently I tried using Andrew Kennan's answer and it didn't work for me for some reason. I used this instead and it worked (note: writing the namespace might be required).

if (typeof(someObject).GetInterface("MyNamespace.IMyInterface") != null)

Answer 6

A variation on @AndrewKennan's answer I ended up using recently for types obtained at runtime:

if (serviceType.IsInstanceOfType(service))
{
    // 'service' does implement the 'serviceType' type
}