How to make a preloader with load external file?

I am currently working wi开发者_Python百科th Flex 4. I successfully use custom preloader by s:application ... preloader="path"..., but i want the preloader to load external file as well, can it do that? How can i call the variables in the preloader?

Thanks for everyone has a look at my question.

Not a readymade solution, but the idea.
If you have simple preloader working, you should know how many bytes it has to load. To load external file, create Loader. Now you have bytesTotal from preloader and bytesTotal from Loader via ProgressEvents from them. To compute percents properly, you need to use sum of bytesLoaded and sum of bytesTotal.