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Flash AS3: Sequential loading with BulkLoader

April 23rd, 2009

BulkLoader is an open source AS3 Library created by Arthur Debert that enables easy loading of multiple assets. This behavior is exactly what I needed for a recent project. I needed to break a large flash website into multiple swfs so that the site preload remained small. I wanted the remaining site pages (individual SWFs) to load in the background, one at a time, after the initial site load. If a user requested a page that hadn’t loaded yet, the background loading would pause and the requested page would load immediately. BulkLoader is designed for exactly this sort of heavy lifting and it saved me a lot of development time.

I’ve created a picture loading demo below to show exactly how this works:

As you can see, I have used BulkLoader as a sequential loader (loading only one image at a time). After bulk loading has begun, you can request any of the images immediately. At this point, BulkLoader will pause the current download and switch to loading the requested image. As soon as that is complete, it will resume the previous download.

There are a few important caveats when using the BulkLoader library:

  • BulkLoader behaves differently on a web server than in the Flash IDE. When testing BulkLoader, it is important to test it on a web server to get accurate results. The Flash IDE is not able to correctly simulate functions such as pause() and loadNow(), so they should be tested in a browser.
  • BulkLoader behavior also varies slightly between browsers . In Firefox3 and Safari, paused downloads are restarted from the beginning when they resume. Internet Exploder 7 actually pauses and resumes downloads correctly (go figure!).

As always, you can download source files here. The code is fairly straightforward and I have added lots of comments. Please note that this sample is designed as a demo only - I sacrificed a lot of elegance in the code for the sake of simplicity.

You can get the latest version of BulkLoader here. You will also find online docs and a very helpful discussion list moderated by Arthur Debert himself. It's a great place to get help using BulkLoader or just drop in and say thanks to Arthur.

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