Explicit Animations - iOS Core Animation - page 167

CATransform3D NSValue id obj = [NSValue

valueWithCATransform3D:transform);

CGImageRef id id obj = (__bridge id)imageRef;

CGColorRef id id obj = (__bridge id)colorRef;

The fromValue , toValue , and byValue properties can be used in various combinations, but
you should not specify all three at once because that could result in a contradiction. For
example, if you were to specify a fromValue of 2, a toValue of 4, and a byValue of 3,
Core Animation would not know whether the final value should be 4 (as specified by
toValue ) or 5 ( fromValue + byValue ). The exact rules around how these properties can be
used are neatly documented in the CABasicAnimation header file, so we won't repeat them
here. In general, you will only need to specify either the toValue or byValue ; the other
values can be determined automatically from context.
Let's try an example: We'll modify our color fade animation from Chapter 7, “Implicit
Animations,” to use an explicit CABasicAnimation instead of an implicit one. Listing 8.1
shows the code.

Listing 8.1 Setting the Layer Background Color with CABasicAnimation

@interface ViewController ()

@property ( nonatomic , weak ) IBOutlet UIView *layerView;
@property ( nonatomic , strong ) IBOutlet CALayer *colorLayer;

@end

@implementation ViewController

- ( void )viewDidLoad
{
[ super viewDidLoad ];

//create sublayer
self .colorLayer = [ CALayer layer ];
self .colorLayer. frame = CGRectMake ( 50.0f , 50.0f , 100.0f , 100.0f );
self .colorLayer. backgroundColor = [ UIColor blueColor ]. CGColor ;
//add it to our view
[ self .layerView. layer addSublayer : self .colorLayer];
}

- ( IBAction )changeColor
{
//create a new random color