flash external preloader to load a swf thats loading another file

I have my preloader loading my main swf where I'm loading ano开发者_Go百科ther swf that contains a background.

When my preloader is done it shows my main swf but it takes a while after that for the background to load.

Whats the easiest way to get my preloader to wait until the background swf is done loading?

Your main swf must somehow communicate this fact to the preloader - there's no way for the preloader to find out for itself. Considering having the main swf fire an event that the preloader is listening for, or just use a callback function.