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Programming Flex 2 by Joey Lott, Chafic Kazoun

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Bootstrapping Flex Applications

Although it would be natural enough to assume that the root of a Flex application is an Application object (because the root tag of the runnable application is an Application tag), it turns out that the default root object is, in fact, of type mx.managers.SystemManager.

In order to understand SystemManager and the bootstrapping process, you have to understand just a little about a Flash Player class called flash.display.MovieClip. The MovieClip class is a display object type which allows you to programmatically work with timelines. Timelines are a feature often used in Flash applications because Flash authoring allows developers to work with timelines through the program interface. Timelines are not used frequently in Flex applications because there is no programmatic way to add frames (the basic units of a timeline) to a timeline. However, timelines and frames are an essential part of SystemManager, and in order to understand how Flex applications work, you must understand a few things about timelines.

A timeline is composed of frames. A frame represents a point in time during the playback of a timeline. This is similar to timeline concepts used in any sort of animation or video program. Because there's no way to programmatically add frames, almost all display objects in Flex applications consist of just one frame. However, SystemManager is the one exception to this rule. SystemManager consists of two frames. This is essential because it enables the ...

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