multimediacollege, Adobe Authorized Training Centre

I was looking for a way to set parameters more quickly to newly added childs and I found out something interesting. (Note that this will not result in faster code execution, it’s merely to type less . I did some testing for the performance, check it out at the bottom of the page.)

Normally when I create a new DisplayObject (sprite, mc, …) that I want to position right after I do it like this:

var mc:MovieClip = new MovieClip();
mc.x = 200;
mc.y = 300;
mc.name = "myTestClip_mc";
...
addChild(mc);

Now this can be shorter right? Creating a temp variable is not a bad practice but I like to do this in an even shorter way. (I remember the initObject parameter of the attachMovieClip function in as2 which was a pretty useful feature.)
Now I already knew you could use the with keyword to set vars more quickly on any object. Unfortunately you loose code completion/intellisense

var mc:MovieClip = new MovieClip();
with(mc)
{
x = 200;
y = 300;
name = "myTestClip_mc";
...
}
addChild(mc);

But still, I need a reference to the object in order to add it to the displaylist afterwards.
Now when browsing the docs I saw that the addChild function returns the element you’ve just added, which is not something to be surprised about, we had this already with createNewMovieClip/AttachMovieClip in as2, but it just didn’t cross my mind to use it that way.

addChild(child:DisplayObject):DisplayObject

So if you combine those two things, the original code can be easily formatted to the following format, which is exactly what I was looking for, short code without creating temporary variables:

with(addChild(new MovieClip()))
{
x = 200;
y = 300;
name = "myTestClip_mc";
...
}

So after I got some feedback I decided to make a small test about the subject. The testfile has 3 functions, test with the method mentioned above, a test with temp vars where I add the child after setting the x/y variables. I added a version where a mc is loaded from the library and a version using a sprite in combination with the drawing api.

Go ahead and try it out! (source)

Notice that there is not that much of a difference in execution time with few iterations. But if you increase the number of iterations, the differences becomes clear pretty fast (tested in ff3 under windows xp, 2.66 ghz, 3 gb ram)