How to avoid 'Method is never used' message?

Question

In the following example, Resharper complains about DoA() method never being used, despite being implemented by the 'AImplementator' class:

namespace Test
{
    public interface A
    {
        // Method 'DoA' is never used
        void DoA();
    }

    public class AImplementator: A
    {
        public void DoA()
        {
            throw new System.NotImplementedException();
        }
    }
}

I can't understand this behavior, since the interface IS being used.

1. Why this happens?
2. How can I fix this warning?

Obs: I can supress the warning using comments or the [UsedImplicitly] attribute. But neither of these options seems to be correct given the situation. I'm using Resharper 9.1.

Answer 1

This warning will only be displayed when the Solution-Wide Analysis is enabled.

The warning is about the usage (in this case e.g. a call) of the interface method. The following example should demonstrate it (note the var vs. interface as local variable type).

var instance = new AImplementator();
// Does NOT make A.DoA() "used":
instance.DoA();

A instanceAsInterface = new AImplementator();
// DOES make A.DoA() "used":
instanceAsInterface.DoA();

Answer 2

To answer other people going here.

If you do have resharper 10.

you can use jetrains annotatoins:

• nuget it into your project: https://www.nuget.org/packages/JetBrains.Annotations
• docs: https://www.jetbrains.com/help/resharper/10.0/Reference__Code_Annotation_Attributes.html

putting the attribute: [UsedImplicitly] above the class will suffice.

What is great to know is that it also works putting it on the base class.

In this case Putting it on interface A will fix the message showing up for all subclasses (great for ioc implementations)

namespace Test
{
    [JetBrains.Annotations.UsedImplicitly]
    public interface A
    {
        // Method 'DoA' is never used
        void DoA();
    }

    public class AImplementator: A
    {
        public void DoA()
        {
            throw new System.NotImplementedException();
        }
    }
}

Tests

Best solution would be to write unit tests to cover these functions. The advantage would be that also your specs are covered.