How to specify a callback/listener in an interface

Question

I am looking for an example of an interface with a listener, so any class implementing the interface also needs to have the listener. For the interface below I wanted to have a listener to callback when the ImageView is loaded. One class will use a bitmap, the other will use a uri. In either case

My interface

public interface ITokenMessageService {

     public void sendAcknowledgement();
     public void sendReceived();
     public void sendFinished();
     public void displayToken(ImageView imageView, [here is where I want the callback]);

}

This may seem rather simple but the queries for interface returned a lot of UX responses and because you implement an interface for a listener, there were a lot of responses for that as well, so I was having trouble finding an example.

Answer 1

public interface ITokenMessageService {

     public void sendAcknowledgement();
     public void sendReceived();
     public void sendFinished();
     public void displayToken(ImageView imageView, YourCallback callback );

     //You could have a get function in your interface
     //thus anything implementing it, needs to have a function that returns
     //the callback, ie it has it. 
     public YourCallback getYourCallback();
}

In reality this doesn't make much sense though, as why would you need to guarantee the implementer also has the callback through an Interface ? If its using the displayToken function it HAS to have it or have access to it anyways, its a moot point.