haxe
class MyComponent extends Box {
    public var lastSelection:String = null;
    
    public function new() {
        super();
        registerEvent(MouseEvent.CLICK, onViewClick);
    }
    
    public override function renderTo(g:Graphics) {
        if (this.isReady == false || this.hidden == true) {
            return;
        }
        
        g.color = Color.Blue;
        g.fillRect(screenX, screenY, this.width / 2, this.height / 2);
        g.color = Color.White;
        
        g.color = Color.Yellow;
        g.fillRect(screenX + this.width / 2, screenY, this.width / 2, this.height / 2);
        g.color = Color.White;
        
        g.color = Color.Red;
        g.fillRect(screenX, screenY + this.height / 2, this.width / 2, this.height / 2);
        g.color = Color.White;
        
        g.color = Color.Green;
        g.fillRect(screenX + this.width / 2, screenY + this.height / 2, this.width / 2, this.height / 2);
        g.color = Color.White;
    }
    
    private function onViewClick(event:MouseEvent) {
        var x = event.localX;
        var y = event.localY;
        var cx = this.width;
        var cy = this.height;
        if (x < cx / 2 && y < cy / 2) {
            lastSelection = "blue";
            dispatch(new UIEvent(UIEvent.CHANGE));
        } else if (x > cx / 2 &&  y < cy / 2) {
            lastSelection = "yellow";
            dispatch(new UIEvent(UIEvent.CHANGE));
        } else if (x < cx / 2 && y > cy / 2) {
            lastSelection = "red";
            dispatch(new UIEvent(UIEvent.CHANGE));
        } else if (x > cx / 2 && y > cy / 2) {
            lastSelection = "green";
            dispatch(new UIEvent(UIEvent.CHANGE));
        }
    }
}

xml
<vbox style="padding: 5px;">
    <button text="Click Me!" onclick="c.width += 20; c.height += 20;" />
    <my-component id="c" width="100" height="100" onchange="sel.text = this.lastSelection" />
    <label id="sel" text="Select something!" />
</vbox>

dispatch(new UIEvent