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Understanding Events and Handlers
A Director movie may be thought of as a series of eventsthings that happen on the Stage or in the Score. Some events are automatic, such as the playhead entering a new frame. Other events are user-initiatedfor example, a click of the mouse button or the pressing of a key on the keyboard.Whenever an event occurs, Director generates a one-word message acknowledging the event. (For example, when the mouse button is released, Director generates the message "mouseUp.") The user doesn't see these messages; they're solely for internal communication within Director. Table 15.1 shows a list of common events that can occur while a movie is playing and the messages those events generate.
EVENT | MESSAGE AND HANDLER NAME |
|---|---|
A window is activated | activateWindow |
A window is closed | closeWindow |
A window is deactivated | deactivateWindow |
Playhead enters frame with a new sprite | beginSprite |
Playhead leaves a sprite | endSprite |
Playhead enters current frame | enterFrame |
Playhead exits current frame | exitFrame |
Playhead enters a frame but hasn't displayed it yet | prepareFrame |
No event occurred | idle |
A key is pressed | keyDown |
A key is released | keyUp |
Mouse button pressed | mouseDown |
Mouse button released | mouseUp |
Mouse pointer enters a sprite | mouseEnter |
Mouse pointer leaves a sprite | mouseLeave |
Mouse pointer stays within a sprite | mouseWithin |
Movie starts playing | startMovie |
Movie stops playing | stopMovie |
Movie is about to start playing | prepareMovie |
Figure 15.3. Every handler has three parts: The first line specifies the event that triggers the handler, the body lists commands that should be executed, and the last line concludes the handler.
The first line always begins with the word on, followed by the message to which the handler should respond. (Handlers are referred to by the name of the message that triggers them. For example, the handler in Figure 15.3 is called a mouseUp handler, because it responds to the message generated when a user releases the mouse button.)
The body of the handler (the indented part) contains the commands that are executed when the handler is triggered. The commands are executed in the order in which they appear in the handler.
The last line always consists of the word end. (This is so Director can know where one handler ends and the next one begins.)
(Note: For convenience, handlers are often described as responding toor being triggered byevents in a movie. There's nothing wrong with using this informal shorthand, as long as you realize that handlers technically respond to the messages generated by events, not to the events themselves.)
