Retired Document
Important: This document may not represent best practices for current development. Links to downloads and other resources may no longer be valid.
Timing
This chapter discusses timing issues when using Core Animation.
Using a Single Timing Function For a Keyframe Animation
The CAKeyframeAnimation
class provides a powerful means of animating layer properties. However, CAKeyframeAnimation
does not allow you to specify a single animation timing function that is used for the entire path. Instead you are required to specify the timing using the keyTimes
property, or by specifying an array of timing functions in the timingFunctions
property.
You can provide a single timing function for the animation by grouping the keyframe animation in a CAAnimationGroup
, and setting the group animation’s timing function to the desired CAMediaTimingFunction
. The animation group’s timing function and duration take precedence over the keyframe animation’s timing properties.
A code fragment that implements this strategy is shown in Listing 1.
Listing 1 Using a single timing function for a keyframe animation
// create the path for the keyframe animation |
CGMutablePathRef thePath = CGPathCreateMutable(); |
CGPathMoveToPoint(thePath,NULL,15.0f,15.f); |
CGPathAddCurveToPoint(thePath,NULL, |
15.f,250.0f, |
295.0f,250.0f, |
295.0f,15.0f); |
// create an explicit keyframe animation that |
// animates the target layer's position property |
// and set the animation's path property |
CAKeyframeAnimation *theAnimation=[CAKeyframeAnimation |
animationWithKeyPath:@"position"]; |
theAnimation.path=thePath; |
// create an animation group and add the keyframe animation |
CAAnimationGroup *theGroup = [CAAnimationGroup animation]; |
theGroup.animations=[NSArray arrayWithObject:theAnimation]; |
// set the timing function for the group and the animation duration |
theGroup.timingFunction=[CAMediaTimingFunction |
functionWithName:kCAMediaTimingFunctionEaseIn]; |
theGroup.duration=15.0; |
// release the path |
CFRelease(thePath); |
// adding the animation to the target layer causes it |
// to begin animating |
[theLayer addAnimation:theGroup forKey:@"animatePosition"]; |
Copyright © 2015 Apple Inc. All Rights Reserved. Terms of Use | Privacy Policy | Updated: 2015-03-09