XBL doesn't work well on panel?

I have found that the xbl element won't init before it shows up. So when I add an xul box element to panel,and bind it to my xbl ,I can't use like this :box.xblMethod(),FF will throw xblMethod is undef开发者_Go百科ined. The question is how can I know when I can call the xblMethod? Did any body encount this problem ? Thanks advance!

You might find you can do the necessary work in the binding's <constructor>.