Adobe 65036570 Scripting Guide - Page 63

ADOBE DIRECTOR 11.0 26 Scripting Dictionary Events, messages, and handlers A key component to creating powerful, useful scripts is an understanding of the concepts and functionality of events, messages, and handlers. Understanding the order in which events and messages are sent and received will help you determine exactly when specific scripts or parts of scripts should run. It will also help you debug scripts when specific actions are not occurring when you expect them to occur. When a movie plays, the following occur: • Events occur in response to either a system or user-defined action. • Messages that correspond to these events are sent to the scripts in a movie. • Handlers within scripts contain the instructions that run when a specific message is received. The name of an event corresponds to the name of the message it generates, and the handler that handles the event corresponds to both the event and the message. For example, when the event named mouseDown occurs, Director generates and sends to scripts a message named mouseDown, which would in turn be handled by a handler named mouseDown. Events There are two categories of events that occur when a movie plays: • System events occur without a user interacting with the movie and are predefined and named in Director-for example, when the playhead enters a frame, when a sprite is clicked, and so on. • User-defined events occur in response to actions that you define. For example, you could create an event that occurs when the background color of a sprite changes from red to blue, when a sound has played five times, and so on. Many system events, such as prepareFrame, beginSprite, and so on, occur automatically and in a predefined order while a movie is playing. Other system events, particularly mouse events such as mouseDown, mouseUp, and so on, do not necessarily occur automatically while a movie is playing, but rather when a user triggers them. For example, when a movie first starts, the prepareMovie event always occurs first, the prepareFrame event always occurs second, and so on. However, the mouseDown and mouseUp events may never occur in a movie unless a user triggers them by clicking the movie. The following lists illustrate the system events that always occur during a movie, and the order in which they occur. When the movie first starts, events occur in the following order: 1 prepareMovie 2 prepareFrame Immediately after the prepareFrame event, Director plays sounds, draws sprites, and performs any transitions or palette effects. This event occurs before the enterFrame event. A prepareFrame handler is a good location for script that you want to run before the frame draws. 3 beginSprite This event occurs when the playhead enters a sprite span. 4 startMovie This event occurs in the first frame that plays. When the movie encounters a frame, events occur in the following order: 1 beginSprite This event occurs only if new sprites begin in the frame. 2 stepFrame 3 prepareFrame