Add this class and use it just like you would a vertical panel. This extends vertical panel and allows you to watch for events on the panel. This class below is only watching for clicks, but you can watch for all the events by adding them to sink events.

public class WatchEventPanel extends VerticalPanel {

/**
* change listener to watch for fired events
*/
private ChangeListenerCollection changeListeners;

/**
* constructor - extending VerticalPanel with event watching
*/
public WatchEventPanel() {

//watch this widgets events
sinkEvents(Event.ONCLICK);

}

/**
* watch for particular browser events - sinkEvents(Events.[ONCLICK|etc])
*/
public void onBrowserEvent(Event event) {
switch (DOM.eventGetType(event)) {
case Event.ONCLICK:
if (changeListeners != null) {
changeListeners.fireChange(this);
}
break;
}
}

/**
* add change listener - watch for changes in this widget
* @param listener
*/
public void addChangeListener(ChangeListener listener) {
if (changeListeners == null)
changeListeners = new ChangeListenerCollection();
changeListeners.add(listener);
}

/**
* remove change listener - remove watching for changes in this widget
* @param listener
*/
public void removeChangeListener(ChangeListener listener) {
if (changeListeners != null)
changeListeners.remove(listener);
}

}

Another way to watch for events on a vertical panel using sinkEvents. In this class, I watch for Click using a changelistener. I observe mouse events using mouselistener. You can observe this verticalPanel widget via using the mouselistener and/or change listener. There are lots of different ways you can configure listeners.

/**
* I use this panel for the drag handler for my composite widgets
* dragHandler = where the mouse holds the widget while dragging
*
* @author Brandon Donnelson
*
* I extend the vertical panel - not a composite widget
*/
public class WatchEventPanel extends VerticalPanel implements SourcesMouseEvents {

private MouseListenerCollection mouseListeners;
private ChangeListenerCollection changeListeners;

/**
* constructor - extending VerticalPanel with event watching
*/
public WatchEventPanel() {

//watch this widget’s mouse events
sinkEvents(Event.MOUSEEVENTS);
}

/**
* watch for browser events - from sinkEvents([MouseEvents])
*/
public void onBrowserEvent(Event event) {

switch (DOM.eventGetType(event)) {
case Event.ONMOUSEDOWN:
if (mouseListeners != null) {
mouseListeners.fireMouseEvent(this, event);
}
if (changeListeners != null) {
changeListeners.fireChange(this);
}
break;
case Event.ONMOUSEMOVE:
if (mouseListeners != null) {
mouseListeners.fireMouseEvent(this, event);
}
break;
case Event.ONMOUSEOUT:
break;
case Event.ONMOUSEOVER:
break;
case Event.ONMOUSEUP:
if (mouseListeners != null) {
mouseListeners.fireMouseEvent(this, event);
}
break;
case Event.ONMOUSEWHEEL:
break;
}
}

/**
* observer stuff
*/
public void addMouseListener(MouseListener listener) {
if (mouseListeners == null)
mouseListeners = new MouseListenerCollection();
mouseListeners.add(listener);
}

public void removeMouseListener(MouseListener listener) {
if (mouseListeners != null)
mouseListeners.remove(listener);
}

/**
* add change listener - watch for changes in this widget
* @param listener
*/
public void addChangeListener(ChangeListener listener) {
if (changeListeners == null)
changeListeners = new ChangeListenerCollection();
changeListeners.add(listener);
}

/**
* remove change listener - remove watching for changes in this widget
* @param listener
*/
public void removeChangeListener(ChangeListener listener) {
if (changeListeners != null)
changeListeners.remove(listener);
}

}