AS2 - 3 Migration

Question

Hi, I am new to Flash CS3 so sorry if this is an easy
question, I found a nice easy example of making a digital clock
online, I followed the example and everything worked using AS2 but
when I tried to do the same in AS3 the _root.onEnterFrame =
function() { at the top of my code did not work. I read in the help
files that this has been changed so I have tried to change this to
work but I have not been successful. Could anyone tell me what the
top line of code should be to get this working as I am unable to
get it right.
Thanks
Mark

Answer 1

Mark,
> I found a nice easy example of making a digital clock
online,
> I followed the example and everything worked using AS2
> but when I tried to do the same in AS3 the
_root.onEnterFrame
> = function() { at the top of my code did not work.
That's part of the change needed, but there's actually a bit
more, too.
Fortunately, the strict nature of AS3 really encourages you
(meaning anyone)
to think through all the bits and pieces of a block of code.
I find that
AS3 has helped me become a better programmer just because it
isn't as
forgiving as AS2 was.
The structure of event handlers in AS3 -- almost across the
board -- is
easy enough to grasp. Check it out:
objectReference.addEventListener(someEvent, someFunction);
In this case, objectReference refers to some object for
which you're
handling an event. You were using _root before, and AS3 no
longer refers to
the same entity with the word "_root". As it turns out, you
didn't
especially neet "_root" in AS2 either. Assuming your code was
in a frame of
the main timeline, you could have used "this" (without the
quotes) or even
simply nothing, as the object the code was *in* (the main
timeline) would be
understood. The someEvent part means the event you're
listening for, and
the someFunction part refers to the function to perform when
that event
occurs. You could either use an anonymous function (like you
were using) or
a named function. I'll show you both.
addEventListener(
Event.ENTER_FRAME,
function(evt:Event):void {
var myDate:Date = new Date();
var myHours:String = myDate.getHours().toString();
var myMinutes:String = myDate.getMinutes().toString();
var mySeconds:String = myDate.getSeconds().toString();
if (myHours.length < 2) {
myHours = "0" + myHours;
if (myMinutes.length < 2) {
myMinutes = "0" + myMinutes;
if (mySeconds.length < 2) {
mySeconds = "0" + mySeconds;
time_txt.text = myHours + ":" + myMinutes + ":" + mySeconds;
So as you can see, the addEventListener() method is used to
assign an
anonymous function to the Event.ENTER_FRAME event. The
addEventListener()
method belongs to the EventDispatcher class, so any class
that inherits from
EventDispatcher is capable of using addEventListener() -- and
that includes
movie clips (the MovieClip class), text fields (TextField),
buttons
(SimpleButton), and tons more. In fact, if you look up
EventDispatcher in
the ActionScript 3.0 Language and Components reference,
you'll be able to
see what it's family tree is, and you can click through the
descendents
until you find objects you're more familiar with, like movie
clips and
buttons. Alternately, you can look up the class entries for
movie clips and
buttons, and you'll see EventDispatcher as an earler ancestor
for both of
those objects.
In the above, the same myDate variable holds an instance of
the myDate
class. The major difference here -- besides the new way of
handling
events -- is that I went with strings for the myHours,
myMinutes, etc.
variables. Originally, they're numbers. That's what the
Date.getHours()
method returns, for example. In AS2, you could do something
like this ...
myHours = "0" + myHours;
... and not get dinged (I've used variations on the above
code tons of
times!) -- and the problem is, really, you're converting the
numeric myHours
variable into a string with that line, because you're
concatenating the
numeric value of myHours with a string of the numeral zero.
ActionScript
3.0 balks at that, and really, fair is fair. myHours *isn't*
a string,
after all, so it's a bit dicey to treat it like one.
So ... in this AS3 translation, I just opted to convert
those numbers to
strings in the first place. Because they're strings, you
can't make numeric
comparisons on them like ...
if (myHours < 10) { ...
... because in the stricter AS3, an attempt of comparison
gives you the
warning, "Hey, bro, myHours is a string! You can't compare a
string to a
number!" (I paraphrase, of course). So instead, I opted to
invoke the
String.length property on each string variable to see if it
has less than
two characters. This comparison amounts to the same thing.
Finally, everything is assigned to the TextField.text
property of your
time_txt instance.
If this were a named function, it might look like this:
addEventListener(Event.ENTER_FRAME, enterFrameHandler);
function enterFrameHandler(evt:Event):void {
var myDate:Date = new Date();
var myHours:String = myDate.getHours().toString();
var myMinutes:String = myDate.getMinutes().toString();
var mySeconds:String = myDate.getSeconds().toString();
if (myHours.length < 2) {
myHours = "0" + myHours;
if (myMinutes.length < 2) {
myMinutes = "0" + myMinutes;
if (mySeconds.length < 2) {
mySeconds = "0" + mySeconds;
time_txt.text = myHours + ":" + myMinutes + ":" + mySeconds;
David Stiller
Co-author, Foundation Flash CS3 for Designers
http://tinyurl.com/2k29mj
"Luck is the residue of good design."