Make your own reusable classes using Flash and AS3

Let's suppose that in your programming experience, you know how to make a Movie Clip draggable with the mouse, and you also know how to write a routine to make a MovieClip respond to the arrow keys and move around the stage. Let's further suppose that you've done both of those tasks many times, and you get to thinking "Wouldn't it be great if I could just write one routine for each task, and then just apply it to future Movie Clips at will?" Enter reusable Classes!

The couple of classes that we'll write together are going to be really cool, but first let's set up a package to store our first classes, and set the classpath so that Flash can find them. This is something that I didn't understand for the longest time, but also something that becomes simple once you "get it."

Packages are just directories (or folders, if you prefer) on your hard drive. Inside the directories are stored one or more class files. The reasons you might want to store classes into separate packages are (1) mostly to avoid naming conflicts, and (2) to group similar classes together.

The key to understanding the whole package thing is to set up one folder on your hard drive as a "portal" directory. At least I think of it as being a portal, or an avenue, or a route, to the folders that lie beneath it. The location of it doesn't matter, it's entirely up to you, but this directory will be designated as being in the classpath. So, go ahead and create a new folder somewhere on your hard drive, and we'll tell Flash to add it to the classpath. I chose to call mine "Classes." Feel free to use that name, or substitute one of your own, because the name doesn't matter much, as it won't be used at all in the package statements of our classes, nor the import statements of our fla files.

There are two ways in Flash to designate a classpath. The first way is in the publish settings for the document, but this only works for one document at a time. I prefer the second way, which sets the classpath for all new documents. So, inside Flash, go to Edit, Preferences. In the Preferences dialog box, click "Actionscript" in the left pane. In the right pane, click the button that says "Actionscript 3.0 settings." In the Actionscript 3.0 Settings dialog box, click the button with the plus sign (+). Next, click the browse button (it looks like a target) so that you can browse your system to find the folder you just created. When you've located the folder, click OK on the browse dialog box. Finally, click OK on the Actionscript 3.0 dialog box, and the Preferences dialog box. Done!