AppleScript_ The Definitive Guide - Matt Neuburg [232]
Another way to edit an applet is to choose its Edit → Edit Script menu item. In a stay-open applet, that menu item can be chosen whenever the applet is idle. In non-stay-open applet, the menus are visible while the startup screen is displayed; thus, the user can start up the applet while holding down the Control key, to force the display of the startup screen, and then choose Edit → Edit Script.
Applet Event Handlers
An applet script may contain certain event handlers (see "Event Handlers" in Chapter 9) which, if present, will be called automatically at specific moments in the lifetime of the applet:
run
The run handler , whether implicit or explicit (see "The Run Handler" in Chapter 9), is called when the applet is started up, either by the user opening it from the Finder or by a script targeting it. (To start up an applet without calling its run handler, tell it to launch.)
reopen
A reopen event handler, if present, is called when the already running applet is summoned to the front by such means as being double-clicked in the Finder or having its icon clicked in the Dock. Merely switching among applications with ⌘-Tab, or telling the applet to activate, does not send a reopen event.
idle
An idle event handler, if present, is called as soon as the run handler finishes executing, and then again periodically while a stay-open applet is running. The value returned by the idle handler is a real number, representing how many seconds later the idle handler should be called again. A return value of 0, or any other value that can't be coerced to a positive real, is treated as 30.
quit
A quit event handler, if present, is called when the applet is about to quit. If it is a stay-open applet, this might be because the user has chosen its Quit menu item; if not, it might be because the applet has been started up and its run handler has finished executing. If the quit handler wishes to permit the applet to quit, it must give the continue quit command.
Warning
An applet having a quit handler that does not give the continue quit command will appear to the user to be impossible to quit (except by force-quitting).
So, for example, here's an annoying little stay-open applet:
on run
display dialog "Howdy!"
end run
on reopen
display dialog "Get to Work!"
end reopen
on quit
display dialog "Farewell!"
continue quit
end quit
on idle
beep
activate
display dialog "Get to Work!"
return 1 * minutes
end idle
An applet is scriptable with respect to its event handlers; that is, you can tell an applet to run, reopen, idle, or quit, and it will execute the respective handler if it has one. If you tell an applet to quit and it has no quit handler, it simply quits. If you tell an applet to idle and it has no idle handler , or to reopen and it has no reopen handler, nothing happens (but the calling script may receive an error).
If an applet is not running, do not tell it to run or you'll confuse yourself. The run handler will be called twice—once because you targeted the applet, and again because you told it to run—and the idle handler will be called as well. To prevent this, tell the nonrunning applet to activate (the run handler will be called once, and the idle handler will be called).
Alternatively, you can tell the nonrunning applet to launch. In that case, neither the run handler nor the idle handler will be called, and no other event handler is called either; if you immediately tell the applet to quit, not even its quit handler is called. An applet launched in this way "comes to life" only if you send it some further Apple event (for example, tell it to launch and then tell it to run).
An idle handler should not be treated as ensuring a precise measure of time; the time interval