Flash Tips Overview

Over the years, there have been little ‘oh, duh’ incidents that have helped me and my team get through troubleshooting Flash projects. I’ve been meaning to create an archive of these incidents to hopefully help some others. While I can’t guarantee that these examples follow “programming principles”, they have gotten us through our projects? and we’ve learned quite a bit along the way. Feel free to send feedback so I can revise or even provide other “alternatives” to these problems/scenarios.

Referencing MovieClip Instances using Variables
For Actionscript Experience Level: Beginner

I’ve been asked a number of times, “How can I refer to an instance name using a string and modify the properties of the instance?” Most of the time, it’s because the author has several instances on the stage named in a sequence such as foo1, foo2, foo3, and wants to be able to refer to one of the movieclips using two variables (”foo” + 2 = foo2) like this:

var mcNum:Number = 2;
var mcName:String = “foo” + mcNum;
mcName._alpha = 30; // change alpha of movieclip to 30 to show effect

This code will not do anything, because there is no movieclip instance name of mcName. If you did a trace on mcName (trace(mcName)), you’ll see an output of “foo2″ because you declared a string variable. Still with me? Okay, here’s how you can do it:

var mcNum:Number = 2;
var mcName:String = “foo” + mcNum;
this[mcName]._alpha = 30; // changes alpha of movieclip to 30 to show effect

So what’s happening here? “this” is a global property that references the path to where your movieclip lives, so if you did a trace(this) on the root stage, it’ll return “_level0″ in the output panel. The brackets next to “this” are essentially allowing you to access the array of “this” (in this case, _level0) which is where the instance name “foo1″ lives. this[mcName]._alpha is the same as this.foo2._alpha.

Of course, if you knew the path to where the movieclip lived, you could hardcode that path like so: _level0[mcName], but, what happens if you wanted to move this code around, maybe within another movieclip nested on the stage? You’d have to update that code, otherwise your code would break if you forgot about it. Programmers will almost always advise against hardcoding absolute paths to objects, whether you’re working in HTML, PHP, or Actionscript. It’s best to keep things modular unless you absolutely need to (pun intended)– the global property “this” will help with that.

This entry was posted on Wednesday, October 18th, 2006 at 11:11 pm and is filed under Actionscript. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.