Why is this an issue?

When a base type explicitly implements a public interface method, property or event, that member is only accessible in derived types through a reference to the current instance (namely this). If the derived type explicitly overrides that interface member, the base implementation becomes inaccessible.

This rule raises an issue when an unsealed, externally visible type provides an explicit member implementation of an interface and does not provide an alternate, externally visible member with the same name.

Exceptions

This rule does not report a violation for an explicit implementation of IDisposable.Dispose when an externally visible Close() or System.IDisposable.Dispose(Boolean) method is provided.

How to fix it

Make the class sealed, change the class member to a non-explicit declaration, or provide a new class member exposing the functionality of the explicit interface member.

Code examples

Noncompliant code example

public interface IMyInterface
{
    void MyMethod();
}

public class Foo : IMyInterface
{
    void IMyInterface.MyMethod() // Noncompliant
    {
        MyMethod();
    }
}

Compliant solution

public interface IMyInterface
{
    void MyMethod();
}

public class Foo : IMyInterface
{
    void IMyInterface.MyMethod()
    {
        MyMethod();
    }

    // This method can be public or protected
    protected void MyMethod()
    {
        // Do something ...
    }
}

Resources

Documentation

• Microsoft Learn - Explicit Interface Implementation