Timer-Based Animation - iOS Core Animation - page 232

NSTimer
Actually, we already did something like that in Chapter 3, “Layer Geometry,” with the
clock example, when we used an NSTimer to animate the hand movement. In that example,
the hand only updated once per second, but the principle is really no different if we speed
up the timer to fire 60 times per second instead.
Let's try modifying the bouncing ball animation from Chapter 10 to use an NSTimer instead
of a CAKeyframeAnimation . Because we will now be calculating the animation frames
continuously as the timer fires (instead of in advance), we need some additional properties
in our class to store the animation's fromValue , toValue , duration , and the current
timeOffset (see Listing 11.1).
Listing 11.1 Implementing the Bouncing Ball Animation Using NSTimer
@interface ViewController ()
@property ( nonatomic , weak ) IBOutlet UIView *containerView;
@property ( nonatomic , strong ) UIImageView *ballView;
@property ( nonatomic , strong ) NSTimer *timer;
@property ( nonatomic , assign ) NSTimeInterval duration;
@property ( nonatomic , assign ) NSTimeInterval timeOffset;
@property ( nonatomic , strong ) id fromValue;
@property ( nonatomic , strong ) id toValue;
@end
@implementation ViewController
- ( void )viewDidLoad
{
[ super viewDidLoad ];
//add ball image view
UIImage *ballImage = [ UIImage imageNamed : @"Ball.png" ];
self .ballView = [[ UIImageView alloc ] initWithImage :ballImage];
[ self .containerView addSubview : self .ballView];
//animate
[ self animate ];
}
- ( void )touchesBegan:( NSSet *)touches withEvent:( UIEvent *)event
{
//replay animation on tap
[ self animate ];