C# Error CS0582 – The Conditional attribute is not valid on interface members

C# Error

CS0582 – The Conditional attribute is not valid on interface members

Reason for the Error & Solution

The Conditional not valid on interface members

ConditionalAttribute is not valid on an interface member.

The following sample generates CS0582:

// CS0582.cs  
// compile with: /target:library  
using System.Diagnostics;  
interface MyIFace  
{  
   [ConditionalAttribute("DEBUG")]   // CS0582  
   void zz();  
}