Was this page helpful?
Your feedback about this content is important. Let us know what you think.
Additional feedback?
1500 characters remaining
Compiler Error CS1721
Collapse the table of content
Expand the table of content

Compiler Error CS1721

Class 'class' cannot have multiple base classes: 'class_1' and 'class_2'

The most common cause of this error message is attempting to use multiple inheritance. A class in C# may only inherit directly from one class. However, a class can implement any number of interfaces.

The following example shows one way in which SC1721 is generated, and then shows two possible ways to avoid the error.

// CS1721.cs
public class A {}
public class B {}
public class MyClass : A, B {}   // CS1721

// One possible fix is to use the following approach instead:
public class A {}
public class B : A {}
public class C : B {}

// Another possible fix is to use interfaces instead of base classes:
public class A {}
public interface B {}
public class C : A, B {}
© 2015 Microsoft