C# syntax: Placing the interface's name in the implementation's declaration

Question

I came across some interesting C# syntax that I'm not familiar with in the source code for the Composite Application Library for WPF's DelegateCommand<T> class.

There are some method declarations which are prefixed with the ICommand interface name, and they do not have accessibility modifiers specified. For example:

bool ICommand.CanExecute(object parameter) { ... }

What is this syntax called and where can I read more about it? I assume there's an implicit public, but I can't figure out what the benefit of specifying the class name is. My guess is that it might just be there for organization.

Answer 1

When you place a method like this, you're saying that this is the explicit implementation of the interface. You can read a good tutorial on MSDN via that link.

Also, a comparison might be helpful for a full view of what this means.

Answer 2

It's termed Explicit Interface Implementation:

If a class implements two interfaces that contain a member with the same signature, then implementing that member on the class will cause both interfaces to use that member as their implementation.

If the two interface members do not perform the same function, however, this can lead to an incorrect implementation of one or both of the interfaces. It is possible to implement an interface member explicitly—creating a class member that is only called through the interface, and is specific to that interface. This is accomplished by naming the class member with the name of the interface and a period.

Explicit Interface Implementation Tutorial