Animating UILabel with CoreAnimation / QuartzCore in iOS App - ios

Question

I actually stuck on a problem with animating a UILabel in my iOS Application.
After 2 days of searching the web for code snippets, still no result.
Every sample I found was about how to animate UIImage, adding it as a subview to UIView by layer. Is there any good example about animating a UILabel?
I found a nice solution for a blinking animation by setting the alpha property, like this:
My function:
- (void)blinkAnimation:(NSString *)animationID finished:(BOOL)finished target:(UIView *)target
{
NSString *selectedSpeed = [[NSUserDefaults standardUserDefaults] stringForKey:#"EffectSpeed"];
float speedFloat = (1.00 - [selectedSpeed floatValue]);
[UIView beginAnimations:animationID context:target];
[UIView setAnimationDuration:speedFloat];
[UIView setAnimationDelegate:self];
[UIView setAnimationDidStopSelector:#selector(blinkAnimation:finished:target:)];
if([target alpha] == 1.0f)
[target setAlpha:0.0f];
else
[target setAlpha:1.0f];
[UIView commitAnimations];
}
Call my function on the UILabel:
[self blinkAnimation:#"blinkAnimation" finished:YES target:labelView];
But how about a Pulse, or scaling animation?

Answer 1

Unfortunately font size is not an animatable property of NSView. In order to scale a UILabel, you'll need to use more advanced Core Animation techniques, using CAKeyframeAnimation:
Import the QuartzCore.framework into your project, and #import <QuartzCore/QuartzCore.h> in your code.
Create a new CAKeyframeAnimation object that you can add your key frames to.
Create a CATransform3D value defining the scaling operation (don't get confused by the 3D part--you use this object to do any transformations on a layer).
Make the transformation one of the keyframes in the animation by adding it to the CAKeyframeAnimation object using its setValues method.
Set a duration for the animation by calling its setDuration method
Finally, add the animation to the label's layer using [[yourLabelObject layer] addAnimation:yourCAKeyframeAnimationObject forKey:#"anyArbitraryString"]
The final code could look something like this:
// Create the keyframe animation object
CAKeyframeAnimation *scaleAnimation =
[CAKeyframeAnimation animationWithKeyPath:#"transform"];
// Set the animation's delegate to self so that we can add callbacks if we want
scaleAnimation.delegate = self;
// Create the transform; we'll scale x and y by 1.5, leaving z alone
// since this is a 2D animation.
CATransform3D transform = CATransform3DMakeScale(1.5, 1.5, 1); // Scale in x and y
// Add the keyframes. Note we have to start and end with CATransformIdentity,
// so that the label starts from and returns to its non-transformed state.
[scaleAnimation setValues:[NSArray arrayWithObjects:
[NSValue valueWithCATransform3D:CATransform3DIdentity],
[NSValue valueWithCATransform3D:transform],
[NSValue valueWithCATransform3D:CATransform3DIdentity],
nil]];
// set the duration of the animation
[scaleAnimation setDuration: .5];
// animate your label layer = rock and roll!
[[self.label layer] addAnimation:scaleAnimation forKey:#"scaleText"];
I'll leave the repeating "pulse" animation as an exercise for you: hint, it involves the animationDidStop method!
One other note--the full list of CALayer animatable properties (of which "transform" is one) can be found here. Happy tweening!