Preloaders, the hardest of the simplest tasks in Flash. Simply put, preloaders are custom-built indicators that inform the viewer that content is being loaded into the Flash player. As easy as they sound implement, creating one that works effectively and correctly can often be a quite frustrating task. This tutorial should help explain the ins and outs of preloaders and help you be better equipped to deal with them on your own.
Basic Kinds of Preloaders

There are generally two kinds of preloaders:

1. Preloaders that load the main, current Flash movie and
2. Preloaders that load additional, external content within an already loaded main movie

When loading the main movie, you are using a preloader that exists within the same movie that you are attempting to load. Because of this, these kinds of preloaders should be (in terms of file size) as small as possible since the preloader itself has to load prior to the rest of the movie before it can even start to function.

When loading external content, such as other Flash movies (swf files) or images, preloader size isn't as important. This is because the preloader for that external content does not exist within the content. Instead, it exists within the current Flash movie which should already be completely loaded, preloader and all.

The complexity of a preloader can range anywhere from a simple, static waiting message to a dynamically updated animation that reflects the status of the content loaded. The difficulty of implementing a preloader obviously increases with complexity. Preloader progress bars are the most common form of preloaders which show a progression bar that displays how much content has been loaded visually.

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