The most straightforward way of doing what you’re referring to is to place a conditional in the enter frame listener and set a variable with mouse events. Declare a var called something like “run” at the top of the script. The contents of the enter frame listener are within if (run) { } (or you can just put this at the first line of the listener if (!run) { return; }). Then a mouse listener sets the run var to true when you want to play the exercise, and, perhaps, a timeline script a the end of the exercise sets the var to false.

Thank you for writing such a great book and providing these exercises. I have learned a lot from you. Would you be able to show us the code to have a functioning play button for these exercises? I suspect the play() methods will not work since the motions are not timeline based. My guess is the ENTER_FRAME in the addEventListener will need to be replaced with a MouseEvent. If this is the case then I am at a lost as to how to get the function to loop. Am I even in the right hemisphere with this?

var circle:Sprite = new Sprite();
circle.graphics.beginFill(0x009900);
circle.graphics.drawCircle(0, 0, 20);
circle.graphics.endFill();
circle.x = 200;
circle.y = 100;

var circle2:Sprite = new Sprite();
circle2.graphics.beginFill(0x990000);
circle2.graphics.drawCircle(0, 0, 40);
circle2.graphics.endFill();
circle2.x = 200;
circle2.y = 100;

var circle3:Sprite = new Sprite();
circle3.graphics.beginFill(0x000066);
circle3.graphics.drawCircle(0, 0, 60);
circle3.graphics.endFill();
circle3.x = 200;
circle3.y = 100;
addChild(circle3);
addChild(circle2);
addChild(circle);

import flash.display.Graphics;
import flash.display.Shape;

var circle:Shape = new Shape();
circle.graphics.beginFill(0x009900);
circle.graphics.drawCircle(200, 100, 20);

var circle2:Shape = new Shape();
circle2.graphics.beginFill(0x990000);
circle2.graphics.drawCircle(200, 100, 40);

var circle3:Shape = new Shape();
circle3.graphics.beginFill(0x000066);
circle3.graphics.drawCircle(200, 100, 60);
addChild(circle3);
addChild(circle2);
addChild(circle);

addEventListener(Event.ENTER_FRAME, scaleCircle, false, 0, true);

function scaleCircle(evt:Event):void {
	circle.scaleX  += .03;
	circle.scaleY  += .03;

	circle2.scaleX  += .02;
	circle2.scaleY  += .02;

	circle3.scaleX  += .01;
	circle3.scaleY  += .01;
}

The only thing I can think of is that you’ve adapted the examples to bring ball1 in from the library? Something like var mc:ball1 = new ball1();. If that’s the case, make sure the class name you gave the symbol in the library is the same as used in your script, including case-sensitivity.

I think I tumbling on some simple error, but can’t see any way around it. I’ve set up my own file with the Event Listener and Function described above(trying to move a symbol’s instance called “ball1″), but wherever I test the Movie I get the following error:
“1046: Type was not found or was not a compile-time constant: ball1.”
Do you have any idea of what I’m doing wrong?
Many thanks for the tutorials, by the way.