Question

First, an example of something that works as expected: (all code was executed in VS2008 immediate window)

25 is IComparable
>> true

25.GetType().GetInterfaces()
>> {System.Type[5]}
>>   [0]: {Name = "IComparable" FullName = ...
>>   [1]: {Name = "IFormattable" FullName = ...
>>   ...

So far so good. Now let’s try on an object where the interface is inherited via a base type:

class TestBase : IComparable
{
    public int CompareTo(object obj) { throw new NotImplementedException(); }
}

class TheTest : TestBase { }

In the immediate window:

(new TheTest()) is IComparable
>> true

(new TheTest()).GetType().GetInterfaces()
>> {System.Type[1]}
>>   [0]: {Name = "IComparable" FullName = "System.IComparable"}

No surprises here either. How come the following code doesn’t show any interfaces then:

wcfChannel = ChannelFactory<IMyServiceApi>.CreateChannel(binding, endpointAddress);

wcfChannel is IMyServiceApi && wcfChannel is ICommunicationObject
>> true

typeof(IMyServiceApi).IsInterface && typeof(ICommunicationObject).IsInterface
>> true

wcfChannel.GetType().GetInterfaces()
>> {System.Type[0]}

How can all of the above be true at the same time?

(edit: added wcfChannel is ICommunicationObject above, which is at this time unexplained by the answer that explains how wcfChannel is IMyServiceApi is true.)

Answer 1

It’s because the type of wcfChannel is the interface itself:

>> channel.GetType().FullName
"MyService.IMyServiceApi"

>> channel.GetType().IsInterface
true

>> channel.GetType() == typeof(IMyServiceApi)
true

.GetInterfaces() returns only the interfaces inherited or implemented, but not the interface itself.

Admittedly, it is unusual for an object instance to actually be of an interface type, but as you mentioned in your comment on the question, the object is actually a transparent proxy. It makes sense for that proxy to be agnostic of the actual interface implementation, and care only about the interface. The fact that .GetType() returns the interface makes the proxy as transparent as possible.