Question

EventHandler.java:

public abstract class EventHandler<E> {
    public abstract void HandleEvent(Object sender, E e);
}

Foo.java:

private OnProgressEventHandler m_OnProgressEventHandler = new OnProgressEventHandler();
private class OnProgressEventHandler extends EventHandler<ProgressEventArgs> {
    public void HandleEvent(Object sender, ProgressEventArgs args) {
        /*...*/
    }
}

ProgressEventArgs.java:

public class ProgressEventArgs extends EventArgs {
    /*...*/
}

Bar.java:

public void addProgressEventListener(EventHandler<EventArgs> listener) {
    m_OnProgress.addListener(listener);
}

This line:

myBarObject.addProgressEventListener(m_OnProgressEventHandler); 

causes:

The method addProgressEventListener(EventHandler) in the
type Bar is not applicable for the arguments (Foo.OnProgressEventHandler)

I don’t understand why it doesn’t compile because OnProgressEventHandler extends EventHandler<ProgressEventArgs>. I’m sure it’s something trivial I missing, but I cant figure why.

Answer 1

Change

public void addProgressEventListener(EventHandler<EventArgs> listener) {
    m_OnProgress.addListener(listener);
}

to

public void addProgressEventListener(EventHandler<? extends EventArgs> listener) {
    m_OnProgress.addListener(listener);
}