Overriding private interface property?

[Joel]

Why does this work:

using System;

namespace ConsoleApplication1
{
class Class1
{
[STAThread]
static void Main(string[] args)
{
DerivedClass d=new DerivedClass();

d.MyProp=10;
Console.WriteLine(d.MyProp.ToString());
}
}

public class DerivedClass : BaseClass, IAbClass
{
#region IAbClass Members

public override int MyProp
{
get{return base.MyProp;}
set{base.MyProp=value;}
}

#endregion
}

public class BaseClass : AbClass
{
}

public abstract class AbClass : IAbClass
{
private int _nAb;
#region IAbClass Members

public virtual int MyProp
{
get{return _nAb;}
set{_nAb=value;}
}

#endregion
}

public interface IAbClass
{
int MyProp{get;set;}
}
}


But not this:
using System;

namespace ConsoleApplication1
{
class Class1
{
[STAThread]
static void Main(string[] args)
{
DerivedClass d=new DerivedClass();

d.MyProp=10;
Console.WriteLine(d.MyProp.ToString());
}
}

public class DerivedClass : BaseClass, IAbClass
{
#region IAbClass Members

public override int IAbClass.MyProp
{
get{return base.MyProp;}
set{base.MyProp=value;}
}

#endregion
}

public class BaseClass : AbClass
{
}

public abstract class AbClass : IAbClass
{
private int _nAb;
#region IAbClass Members

public virtual int IAbClass.MyProp
{
get{return _nAb;}
set{_nAb=value;}
}

#endregion
}

public interface IAbClass
{
int MyProp{get;set;}
}
}

TIA
</joel>

 

[Joakim Karlsson]

The construct

class MyClass : IAbClass
{
int IAbClass.MyProp
{
...
}
}

is called an explixit interface implementation. This means that this
method is considered private unless you access the object as an
IAbClass. Therefore you cannot make it virtual nor override it.

See

http://msdn.microsoft.com/library/d.../en-us/csspec/html/vclrfcsharpspec_13_4_1.asp

for more information.

Regards,
Joakim