iPad: Animate UILabels color changing.

Question

I have a label which pops up displaying points in my application. I am using the following code to make the label get larger in scale, then smaller. I would also like to animate the color changing from purple to green. Can someone point me to a resource in achieving this?

mLabel.textColor = [UIColor purpleColor];

 [UIView beginAnimations:nil context:NULL];
 [UIView setAnimationDuration:1.0];
 [UIView setAnimationDelegate:self];
 mLabel.transform = CGAffineTransformMakeScale(1.5,1.5);
 [UIView setAnimationRepeatCount:1];
 mLabel.transform = CGAffineTransformMakeScale(0.5,0.5);
 mLabel.textColor = [UIColor greenColor];
 [UIView commitAnimations];

Answer 1

Add this before your call to commitAnimations:

[UIView setAnimationTransition:UIViewAnimationTransitionNone forView:mLabel cache:YES];

Answer 2

Unfortunately, the color doesn't animate with UIView animations. The answers to this question give some good workarounds without using Core Animation.

If you don't mind using a CATextLayer instead of a UILabel, then the color (and the scaling in your example) can be animated like this:

#import <QuartzCore/QuartzCore.h>
//Also need to add QuartzCore framework to project (as well as the import).
//
-(void)animateTextLayer {

CGFloat animationDuration = 5;

CATextLayer *textLayer = [CATextLayer layer];
[textLayer setString:@"Hello World"];
[textLayer setForegroundColor:[UIColor purpleColor].CGColor];
[textLayer setFontSize:30];
[textLayer setFrame:CGRectMake(20, 200, 300, 40)];
[[self.view layer] addSublayer:textLayer];

CABasicAnimation *colorAnimation = [CABasicAnimation 
                                     animationWithKeyPath:@"foregroundColor"];
colorAnimation.duration = animationDuration;
colorAnimation.fillMode = kCAFillModeForwards;
colorAnimation.removedOnCompletion = NO;
colorAnimation.fromValue = (id)[UIColor purpleColor].CGColor;
colorAnimation.toValue = (id)[UIColor greenColor].CGColor;
colorAnimation.timingFunction = [CAMediaTimingFunction 
                                 functionWithName:kCAMediaTimingFunctionLinear];

CAKeyframeAnimation *scaleAnimation = [CAKeyframeAnimation 
                                        animationWithKeyPath:@"transform"];
NSArray *scaleValues = [NSArray arrayWithObjects:
    [NSValue valueWithCATransform3D:CATransform3DScale(textLayer.transform, 1, 1, 1)],
    [NSValue valueWithCATransform3D:CATransform3DScale(textLayer.transform, 1.5, 1.5, 1)],
    [NSValue valueWithCATransform3D:CATransform3DScale(textLayer.transform, 0.5, 0.5, 1)], nil];
[scaleAnimation setValues:scaleValues]; 
scaleAnimation.fillMode = kCAFillModeForwards;
scaleAnimation.removedOnCompletion = NO;

CAAnimationGroup *animationGroup = [CAAnimationGroup animation];
animationGroup.duration = animationDuration;
animationGroup.timingFunction = [CAMediaTimingFunction 
                                functionWithName:kCAMediaTimingFunctionLinear];
animationGroup.fillMode = kCAFillModeForwards;
animationGroup.removedOnCompletion = NO;
animationGroup.animations = 
        [NSArray arrayWithObjects:colorAnimation, scaleAnimation, nil];

[textLayer addAnimation:animationGroup forKey:@"animateColorAndScale"];
}