Basic AS3

Question

Hi,
I'm trying to learn AS3. I was very comfortable with AS2, but
now even the most basic things seem impossible for me. If someone
could give me a hand with this I would really appreciate it. This
is a basic AS2 example that I want to be able to replicate in AS3
and from them learn more about the logic behind it:
In AS2:
I could have a movie clip act like a button, and add
properties to it to be called later.
// myClip is a movie clip on the stage
// create a new property for it: temperature
myClip.temperature = '57F';
// have the clip trace the value of temperature once it is
pressed
myClip.onPress = function(){
trace (this.temperature);
so the question is, how do you do something like this in AS3.
I have tried many different ways and none seem to work.
Thanks so much for any help.

Answer 1

SummerLongSince,
> I'm trying to learn AS3. I was very comfortable with
AS2,
> but now even the most basic things seem impossible for
me.
Have you read any of the migration articles published in
Adobe's Dev
Center? These may likely give you a good, general purpose
start with the
new stuff.
> In AS2:
> I could have a movie clip act like a button, and add
properties
> to it to be called later.
This hasn't changed in AS3; not in principle, anyway. In
your example
code, the event handling syntax has changed.
> myClip.temperature = '57F';
> myClip.onPress = function(){
> trace (this.temperature);
> }
In AS3, that could be rendered like this:
myClip.buttonMode = true;
myClip.temperature = "57F";
myClip.addEventListener(
MouseEvent.MOUSE_DOWN,
function(evt:MouseEvent):void {
trace(evt.target.temperature);
Let's take a quick look at the differences. The first line
instructions
Flash Player to show the finger cursor when the mouse is
rolled over the
myClip instance. Without that line, the event handling still
takes place,
but because this is a movie clip symbol and not a button, the
cursor does
not automatically change from the default arrow shape.
The second line is identical to the first line in your
example. I used
double quotes, but it doesn't make any difference in this
case.
The remaining lines show the biggest difference. The
structure of AS3
event handling goes like this:
object.addEventListener(eventToListenFor, functionToPerform);
There are additional parameters (optional) you may provide
after these
first two, but the ones shown are the basic necessities: what
am I
listening for? what should I do when I encountered the
dispatched event.
As you can see, I split these two parameters over a number
of lines, but
the principle is the same (and honestly, not unlike the
principle in the AS2
version ... even there, the same concept applies: what am I
listening for?
what should I do when that thing occurs?).
AS3 event handling is similar to one of the *four* (yes,
four!) ways
event handling was possible in AS2. There was the
on()/onClipEvent()
approach, the newer dot notation approach (as used in your
example), the
addListener() method, and finally (for v2 Components) the
addEventListener()
method. In AS3 -- barring a teensy example or two in video
programming --
event handling is managed the same way. This consistency,
alone, marks a
significant improvement to me. Once you know it, you know it.
Not that instead of the global "this" property, the AS3
version's
trace() statement refers to the expression evt.target. The
variable evt
(short for "event") is found between the parentheses of the
function
literal. The name evt is arbitrary, but it refers to the
MouseEvent
instance passed into the function when the
MouseEvent.MOUSE_DOWN event is
dispatched. The MouseEvent instance features a target
property, and in AS3,
that property refers to the object that dispatched the event
in the first
place, which makes the expression "evt.target" equivalent to
"this" in this
case. An alternative would simply be to replace
avt.target.temperature with
myClip.temperature in the trace() statement.
David Stiller
Co-author, Foundation Flash CS3 for Designers
http://tinyurl.com/2k29mj
"Luck is the residue of good design."