ActionScript for Flash MX: The Definitive Guide, Second Edition

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

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Chapter 8: Loop Statements

Note that our time-based movement might appear jerky if the frame rate suddenly

changes. We could smooth things out by using an elapsed-time measurement that

averages the time between a series of frames instead of just two.

An Alternative to Timeline Loops:

setInterval( )

As of Flash Player 6, we can use setInterval( ) to execute a function every n millisec-

onds. For example, the following code creates a function, moveBall( ), that moves the

ball_mc movie clip 10 pixels to the right, and then uses setInterval( ) to execute that

function every 20 milliseconds.

moveBall = function ( ) {

_root.ball_mc._x += 10;

}

ballMoverID = setInterval(moveBall, 20);

To stop our interval, we can later use:

clearInterval(ballMoverID);

Like a timeline loop or an onEnterFrame( ) loop, setInterval( ) can execute a block of

code indefinitely, and it allows for screen updates between iterations. However, the

setInterval( ) function is not tied directly to a movie’s frame rate (though it is affected

by it). For complete details, see setInterval( ) in the Language Reference.

Onward!

Well, we’ve come pretty far. The end of this chapter marks a milestone—it ends our

examination of the ActionScript statements. This means we have variables, data,

datatypes, expressions, operators, and