.AS File Format – Events

on() on buttons

The script of a button instance in the FLA is made of on blocks, each listing one or more events. Flash MX also allows them on movie clip instances, which then act as buttons.

on (release, releaseOutside) {
    _root.gotoAndStop("menu");
}
on (keyPress "<Enter>") {
    _root.gotoAndStop("menu");
}

Code in an on block runs in the scope of the timeline the button is on, so this and unqualified names refer to that timeline, not to the button.

onClipEvent() on movie clips

The script of a movie clip instance in the FLA is made of onClipEvent blocks, each for one event. The code runs in the scope of the clip itself.

The mouse and key events reach every clip that has a handler for them, not only the one under the pointer. Calling updateAfterEvent() in a mouse or key handler redraws the screen at once instead of at the next frame.

onClipEvent (load) {
    speed = 4;
}
onClipEvent (enterFrame) {
    if (Key.isDown(Key.RIGHT)) _x += speed;
    if (Key.isDown(Key.LEFT))  _x -= speed;
}

Handler properties (Flash MX)

From Flash Player 6 an event handler can be a function stored in a property of the object, set and replaced by any script. Setting one of the button events on a movie clip makes it act as a button, with the hand pointer. Setting the property to null, or deleting it, stops the handler.

ball_mc.onEnterFrame = function () {
    this._x += 4;
    if (this._x > Stage.width) delete this.onEnterFrame;
};

var news = new XML();
news.ignoreWhite = true;
news.onLoad = function (success) {
    if (success) showHeadlines(this.firstChild);
};
news.load("news.xml");

A clip’s onLoad set by a script after the clip exists comes too late to run; it is useful on the prototype of a class registered with Object.registerClass.

Listeners

Some objects tell any number of listener objects about events. A listener is any object with methods named after the events; it is registered with addListener and removed with removeListener.

Any object can broadcast its own events with the AsBroadcaster object, which Flash MX includes but does not document:

var scoreBoard = new Object();
AsBroadcaster.initialize(scoreBoard);   // adds addListener, removeListener,
                                       // broadcastMessage and _listeners
var display = new Object();
display.onScore = function (points) { score_txt.text = points; };
scoreBoard.addListener(display);
scoreBoard.broadcastMessage("onScore", 120); // calls display.onScore(120)

Timers

Flash 5 has no timers; repeated work runs in onClipEvent(enterFrame) or in a loop of frames that go back to each other.