Macromedia flex 2 Manual

240

Creating Effects

In this example, Tween object invokes the

onTweenUpdate()

callback method on a regular

interval, passing it values between

angleFrom

and

angleTo

. At the end of the effect, the

Tween object calls the

onTweenUpdate()

callback method with a value of

angleTo

. By

invoking the

onTweenUpdate()

callback method at regular intervals throughout the duration

of the effect, the target component displays a smooth animation as it rotates.

You use your new effect in an MXML application, as the following example shows:

<?xml version="1.0"?>

<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
xmlns:MyComp="myEffects.*">

<MyComp:Rotation id="Rotate90"
  angleFrom="0" angleTo="360"
  duration="1000"/>

<mx:Image source="@Embed(source='../assets/myImage.jpg')"
  mouseDownEffect="{Rotate90}"/>

</mx:Application>

In this example, you use the effect to rotate an image when the user clicks it.

Writing an effect for a transition

Transitions define how a change of view state appears on the screen. You define a transition by
using a combination of the Flex effect classes. For more information on transitions, see
Chapter 28, “Using Transitions,” in Flex 2 Developer’s Guide.

You can define your own custom effects for use in transitions. To do so, you have to account
for the effect being used in a transition when you override the

EffectInstance.play()

method. The

EffectInstance.play()

method must be able to determine default values for

effect properties when the effect is used in a transition.

Defining the default values for a transition effect

Like any effect, an effect in a transition has properties that you use to configure it. For
example, most effects have properties that define starting and ending information for the
target component, such as the

xFrom

yFrom

xTo

, and

yTo

properties of the

Move

effect.