Flex DownloadProgressBar preloader override

I'm watching this video, which is pretty good http://www.gotoandlearn.com/play?id=108 It shows how to inherit from DownloadProgressBar to create a customer preloader for your flex app. The DownloadProgressBar class has an overridable getter for the property 'preloader.' Isn't this poor design? What does a property called preloader hav开发者_JAVA百科e anything to do with a class for a DownloadProgressBar?

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The preloader property is write-only, so there is no overridable getter. As for it's purpose, from the documentation:

The Preloader class passes in a reference to itself to the display class so that it can listen for events from the preloader