是否可以访问接口类型的其他成员？

Question

I'm curious if this is possible, and if not, what are the reasons behind it if any, and how would one handle this programming scenario?

Let's say i have this interface:

public interface IBook
{
    void BookClient();
    void CancelClient();
}

and i have this class that implements the above interface:

public class Photographer : IBook
{
     public void BookClient()
     {
        // do something
     }

     public void CancelClient()
     {
        // do something
     }

     // non-interface methods
     public void SaveClients()
     {
        // do something
     }

     public void DeleteClients()
     {
        // do something
     }
} 

Now if I assign this class to an interface type somewhere in my code such as:

IBook photo;
photo = new Photographer();

Is it possible to do this:

// non-interface member from the Photographer class
photo.SaveClients();

Can someone straighten me out on this issue and perhaps point me in the right direction regarding this. Thanks.

Answer 1

Yes, it's possible, but you have to cast your photo into Photographer first:

// non-interface member from the Photographer class
((Photographer)photo).SaveClients();

It's not possible with just photo.SaveClients() syntax, because you can easily create another class:

class TestClass : IBook
{
    public void BookClient()
    {
       // do something
    }
     public void CancelClient()
    {
       // do something
    }
}

And use it like that:

IBook photo;
photo = new Photographer();
photo = new TestClass();

// what should happen here?
photo.SaveClients();

So as long as you use the variable as an interface implementation, you can only access member declared in that interface. However, the object is still a class instance, so you can use other class members, but you have to explicitly cast to that type first.

Answer 2

Interface types can only reference interface members. You're attempting to invoke a member of the class which is not part of the interface.

You can try (can't test right now):

IBook photo;
photo = new Photographer();

(photo as Photographer).SaveClients();
// or
((Photographer)photo).SaveClients();

Answer 3

Yes, it's possible, using reflection. Also you can cast to Photographer and then call SaveClients() .

In my opinion a good solution is defining each group of actions you need to call in an interface, then, cast to that interface, and call the method you need:

public interface IBook
{
    void BookClient();
    void CancelClient();
}

public interface IClient
{
    void SaveClients();
}

And then use as:

IBook photo = new Photographer();
// now cast photo object as a IClient
IClient client = photo as IClient;
if (client != null)
{
    client.SaveClients();
}