C# Error CS1722 – Base class ‘{0}’ must come before any interfaces

C# Error

CS1722 – Base class ‘{0}’ must come before any interfaces

Reason for the Error & Solution

Base class ‘class’ must come before any interfaces

When specifying a class to inherit from and interfaces to implement, the class name must be specified first.

Example

The following sample generates CS1722.

// CS1722.cs  
// compile with: /target:library  
public class A {}  
interface I {}  
  
public class MyClass : I, A {}   // CS1722  
public class MyClass2 : A, I {}   // OK