ActionScript for Flash MX: The Definitive Guide, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 8: Loop Statements

Conceptually, the loop statement has the right approach—it repetitively updates the

position of

ball_mc by small amounts, which should give the illusion of movement.

However, in practice,

ball_mc doesn’t move each time its _x position is changed,

because the Stage isn’t updated between loop iterations. Instead, we’d see

ball_mc

suddenly jump 500 pixels to the right—10 pixels for each of the 50 loop iterations—

after the script completes.

To allow the Stage to update after each execution of the

ball_mc._x += 10; state-

ment, we can use a timeline loop like this:

// CODE ON FRAME 1

ball_mc._x += 10;

// CODE ON FRAME 2

this.gotoAndPlay(1);

Because Flash updates the Stage between any two frames, the ball will appear to ani-

mate. But the timeline loop completely monopolizes the timeline it’s on. While it’s

running, we can’t animate any other content on that timeline. A better approach is to

put our timeline loop into an empty, two-frame movie clip. We’ll get the benefit of a

Stage update between loop iterations without freezing a timeline we may need for

other animation.

Creating an Empty-Clip Timeline Loop

The following steps show how to create an empty-clip timeline loop:

1. Create a new Flash movie.

2. Create a movie clip symbol, named ball, that contains a circle ...