Learning ActionScript 3.0

One of the questions about ActionScript 3 that I am most often asked is how to send arguments to a listener function along with an event. Recently, a reader named Jim asked just such a question.

To provide some background for this question, you could send argument data to a standard function like this?

function showMsg(msg:String):void {
    trace(msg);
}
showMsg("Claire");

However, in an event listener, only one argument is allowed in the listener function: the argument responsible for receiving the event data. Using a standard mouse click listener as an example…

stage.addEventListener(MouseEvent.CLICK, showMsg, false, 0, true);
function showMsg(evt:MouseEvent):void {
    trace("hello");
}

…the kind of question asked is, can you do something like this:

stage.addEventListener(MouseEvent.CLICK, showMsg, "hello",
                       false, 0, true);
function showMsg(evt:MouseEvent, msg:String):void {
    trace(msg);
}

The answer is, not out of the box. The existing AS3 events do not provide for this capability. However, to answer Jim’s question, the best way to pass arguments with an event is to create your own event class by extending AS3’s Event class.

Continue reading ‘Passing Arguments with Events’

Thanks to Nick, we discovered an error in the document classes that accompany the source code for Chapter 3. The error has been corrected, and the archive has been replaced. This has nothing to do with the book, so this only applies to those early coders who downloaded the Chapter 3 source archive prior to January 12, 2008.

We introduce syntax and concepts early on in a way that allows us to focus closely on the topics themselves, without having to dive immediately into classes. We then use classes more and more as we progress through the chapters.

However, if you already have some experience with classes (or want to start pushing yourself to this ideal early on), we also provide a second copy of all the timeline examples, using document classes instead. This way you can experiment with both approaches and pick the style that suites you best at the outset of the book.

So, none of the timeline examples were affected and, if you only need to think about this if you downloaded the Chapter 3 archive before January 12th.

Thanks Nick!