Conditional member 'member' cannot implement interface member 'base class member'
ConditionalAttribute cannot be used on the implementation of an interface, for example, on the implementation of an interface method.
The following sample generates CS0629:
interface MyInterface { void MyMethod(); } public class MyClass : MyInterface { [System.Diagnostics.ConditionalAttribute("debug")] public void MyMethod() { // CS0629, remove the conditional attribute } public static void Main() { } }