ActionScript for Flash MX: The Definitive Guide, Second Edition

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

Timeline and Clip Event Loops

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Timeline and Clip Event Loops

The loops we’ve looked at so far cause the interpreter to execute blocks of code

repeatedly. Most of your loops will be of this “ActionScript-statement” type. Some-

times it’s desirable to create a timeline loop by looping Flash’s playhead in the time-

line. To do so, attach a series of statements to any frame; on the next frame, attach a

gotoAndPlay() function whose destination is the previous frame. When the movie

plays, the playhead will cycle between the two frames, causing the code on the first

frame to execute repeatedly.

We can make a simple timeline loop by following these steps:

1. Create a new Flash movie.

2. On frame 1, attach the following statement:

trace("Hi there! Welcome to frame 1");

3. On frame 2, add a blank keyframe and attach the following statements:

trace("This is frame 2");

this.gotoAndPlay(1);

4. Select Control ➝ Test Movie.

When we test our movie, we see an endless stream of the following text:

Hi there! Welcome to frame 1

This is frame 2

Hi there! Welcome to frame 1

This is frame 2

Timeline loops can do two things ordinary loops cannot:

• They can execute a block of code an infinite number of times without causing an

error.

• They can execute a block of code that requires a Stage update between loop

iterations. ...