Classes and Movie Clips - Page 1

In Flash CS3, you have support for creating ActionScript 3.0 (AS3) projects. Besides allowing you to write code in the new AS3 language, there are some subtle differences that may go unnoticed unless you are actively looking for new things. One such difference is what happens when you create or convert something into a new movie clip.

With AS3 projects, when you convert or create something into a movie clip, you specify the name of your movie clip like you always did. This time around, though, what happens is that you not only create a new movie clip object, you also have access to the class that defines your new movie clip.

By accessing the class and writing code directly inside it, you can bypass adding code using the timeline. For example, the following animation was created by me adding code to the movie clip's class file:

The actual code is defined inside the class itself. In other words, I didn't write any code on the timeline at all, and that is different from what you saw in my earlier Animating Dynamic Movie Clips tutorial where everything was written on the timeline.

In this article, I will explain how to take a movie clip, create a class file for it, and write some code inside the class file to create the animation you see above. Since you are already here, I will also explain how the animation works to create the circular motion you see above :-)

Let's Get Started
First, you will need to create a movie clip. For this article, simply create a solid blue circle movie clip and, in the Library, give it the class name BlueCircle. If you don't know how to do that, feel free to read the detailed instructions below. Otherwise, jump on over to the next page!

Creating the BlueCircle MovieClip:
The following instructions explain how to setup your movie and specify the blue circle:

1. First, create a new animation in Flash CS3, and be sure to set your document type to be Flash File (ActionScript 3.0). From the Properties panel, click the button next to the Size text and set the animation's width and height to 300 pixels by 200 pixels respectively:

[ set your animation's width/height to 300 by 200 ]

2. While you are at the Properties panel, set the frame rate to 25.
3. Now that our stage's width and height have been setup just the way we want, let's draw a circle. Using the Circle tool, draw a circle with a blue solid-fill color:

[ draw a blue, solid, filled circle ]

4. Make sure your circle has been selected and press F8 or go to Modify | Convert to Symbol. The Convert to Symbol window will appear. For name, enter circle and make sure the Movie Clip option has been selected:

[ give your symbol the name circle and make sure it is also set to be a movie clip ]

Do not hit OK just yet. Let's make some more modifications.

5. From the same Convert to Symbol window, find the area marked Linkage. If you do not see the Linkage area, press the Advanced button to display it. Check the box that says Export for Actionscript. A few lines above that, in the Class field, replace whatever text is displayed (probably circle) with the text BlueCircle:

[ check 'Export for ActionScript and enter BlueCircle for your class ]

The Base class field will automatically be populated for you, but if it hasn't, make sure to enter flash.display.MovieClip as shown in the above image.

6. Press OK to close the Convert to Symbol window. After you have pressed OK, you will see your Library display your newly created symbol:

[ your circle in your Library ]

If you do not see your Library, press Ctrl + L to display it.

7. At this point, your circle movie clip is stored in the Library, and you have a copy of that same clip on your stage right now. Save this file as rotatingCircles.fla.

At this point, you should see a blank stage with your Library displaying the circle movie clip with the class name BlueCircle. Right now, nothing is really being done. We'll change that on the next page when you create the BlueCircle class file and add some code.

Onwards to the next page!

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