How to handle mouse wheel event?

mycomp.Myimg = zk.$extends(zul.Widget, {

    $define: {
        src: function(v){
            var n = this.$n();
            if (n) 
                n.src = v || '';
        }
    },
    
    bind_: function(){// after compose
        this.$supers('bind_', arguments);
        
        var node = this.$n();
        if (node.addEventListener) 
            node.addEventListener('DOMMouseScroll', this.proxy(this.wheel), false);
        
        node.onmousewheel = this.proxy(this.wheel);
    },
    
    domAttrs_: function(no){
        var attr = this.$supers('domAttrs_', arguments);
        if (!no || !no.content) 
            attr += ' src="' + (this._src || '') + '"';
        return attr;
    },
    
    redraw: function(out){
        out.push('<img', this.domAttrs_(), '/>');
    },
    
     zoom: function(range){
        var node = jq(this.$n()),
              w = node.width(),
              h = node.height();

        node.width(w * range);
        node.height(h * range);
        this.fire("onMouseWheel",{data: });
    },
	
	
    handle: function(delta){		
        if (delta < 0) 
            this.zoom(0.7)
        else 
            this.zoom(1.2)
    },
    
    wheel: function(event){
        var delta = 0;
        if (!event) /* For IE. */ 
            event = window.event;
        if (event.wheelDelta) { /* IE/Opera. */
            delta = event.wheelDelta / 120;
            if (window.opera) 
                delta = -delta;
        }
        else 
            if (event.detail) {
                delta = -event.detail / 3;
            }
        if (delta) 
            this.handle(delta);
        if (event.preventDefault) 
            event.preventDefault();
        event.returnValue = false;
    }    
});

public class MyImg extends XulElement{
	
	private String _src;
	
	
	static {		
		addClientEvent(MyImg.class, "onMouseWheel", CE_REPEAT_IGNORE);
	}
		
	public String getSrc() {
		return _src;
	}

	public void setSrc(String src) {
		if (src != null && src.length() == 0)
			src = null;

		_src = src;
		smartUpdate("src", new EncodedURL());
	}

	private class EncodedURL implements org.zkoss.zk.ui.util.DeferredValue {
		public Object getValue() {
			return getEncodedURL();
		}
	}
	
	private String getEncodedURL() {
		return getDesktop().getExecution().encodeURL(_src);
	}
	
	public void service(org.zkoss.zk.au.AuRequest request, boolean everError) {
		final String cmd = request.getCommand();		

		if (cmd.equals("onMouseWheel")) {
			final JSONArray data = (JSONArray) request.getData().get("data");
			Events.postEvent(new Event(cmd, this, data.get(0)));
			
		} else super.service(request, everError);
	}
	
	protected void renderProperties(org.zkoss.zk.ui.sys.ContentRenderer renderer)
			throws IOException {
		super.renderProperties(renderer);					
		renderer.render("src", getEncodedURL());		
	}
 }

<zk>
	<myimg src="item1.jpg" onMouseWheel='alert("zoom = " + event.data);'/>
</zk>