C# Interface implemented by empty abstract class

Question

Can I leave an abstract class that implements interfaces empty and imply that all the methods/properties in the interface are abstract within my class. It appears that I have to write them out again in the abstract class but I really want to avoid this duplication.

My reason is I have a couple of interfaces with different accessors, one public and one internal, that I want to bring together so I have an abstract class that implements them both that can then be extended.

public interface ISomePublicProperties {
    int PropertyOne {get;}
}

internal interface ISomeInternalProperties {
    int PropertyTwo {get;}
}

public abstract class SomeClass : ISomePublicProperties, ISomeInternalProperties {}

But the compiler complains that SomeClass does not implement interface method ISomePublicProperties.PropertyOne and ISomeInternalProperties.PropertyTwo

Is there anyway in C# (I know Java allows this) that I can leave the abstract class empty implementing interfaces?

Have you tried just creating a virtual stub method to shut the compiler up? — FreeAsInBeer
– FreeAsInBeer, Commented Mar 31, 2011 at 3:33

Matt Greer · Accepted Answer · 2011-03-31 03:39:49Z

16

Nope. In C# the abstract class must fully implement the interface. Note it can implement it with abstract methods and abstract properties. It's one little thing about C# that has always bugged me.

edited Mar 31, 2011 at 3:39

answered Mar 31, 2011 at 3:34

Matt Greer

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1 Comment

yoyo Over a year ago

While you can implement with abstract properties, it seems you can't implement explicitly with abstract properties. The following complains that abstract members cannot be private -- "abstract int ISomePublicProperties.PropertyOne { get; }". Unfortunate.

Andrew Cooper · Accepted Answer · 2011-03-31 03:44:49Z

3

The only way to do it is create virtual properties with no implementation. These are then overridden in your derived classes.

public abstract class SomeClass : ISomePublicProperties, ISomeInternalProperties 
{
    public abstract int PropertyOne { get; }
    internal abstract int PropertyTwo { get; }
}

edited Mar 31, 2011 at 3:44

answered Mar 31, 2011 at 3:37

Andrew Cooper

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3 Comments

aqwert Over a year ago

I think he wants to avoid to have something like public abstract int Property { get; }

kevin Over a year ago

Thanks for the responses but I really wanted to avoid the duplication of the interfaces into the abstract class - I just wanted the abstract class to be empty and the extenders of the class to implement the interfaces.

Matt Greer Over a year ago

This doesn't work because a virtual property must still have an implementation. You can add setters to them to make them auto properties (depends on the situation if that is a good idea or not), or make them abstract. Making them abstract is the closest thing possible to what the OP wants. Java handles this better than C# :)

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