从多个继承同一个超类的类实现回调接口时发生冲突

Question

I have a superclass with some generic behavior for downloading stuff called MySuperclass . This class has a callback interface for further use of the payload.

public class MySuperclass {

    public interface MyDownloadListener{
        void onDownload(Object payload);
    }

    private MyDownloadListener listener;
    ...

    public void download(){
        ...
        listener.onDownloaded(response);
    }

}

I derive multiple classes from MySuperclass , here called MySubclassA and MySubclassB .

public class MySubclassA extends MySuperclass{
    ...
}

public class MySubclassB extends MySuperclass{
    ...
}

The conflict occurs when I try to use both subclasses in a third class. I would have to do something like

public class MyClass implements MySubclassA.MyDownloadListener, MySubclassB.MyDownloadListener{
    ...
    public void onDownloaded(Object payload){
        // here is the conflict
    }

}

but this doesn't work because I can't distinguish between the two different callback interfaces. How can I solve this?

Answer 1

The quickest solution: Provide a sender object which calls your callback interface:

public interface MyDownloadListener{
   void onDownload(Object payload, Object sender);
}

In your super class:

public class MySuperclass {
   ...
   public void download(){
      listener.onDownload(response, this);
   }
}

In your listener object:

public class MyClass implements MySubclassA.MyDownloadListener, MySubclassB.MyDownloadListener{
    ...
    public void onDownload(Object payload, Object sender){
        if(sender instanceof MySubclassA){
            ...
        }
        if(sender instanceof MySubclassB){
            ...
        }
    }
}