Quickly Build an Input-Driven Game - Beginning iOS6 Games Development - page 89

For each UIView , coinViewA and coinViewB , we will be creating two CABasicAnimation objects. When
we create the CABasicAnimation object animScaleDown , we specify that this CABasicAnimation will be
manipulating the value of scale on the property transform . We specify the starting value of the scale
by setting the fromValue of animScaleDown , and we specify the ending value by setting the toValue .
The value duration indicates how many seconds we want this animation to take. By specifying the
timingFunction , we control the rate at which this animation will take place. In this case, we indicate
kCAMediaTimingFunctionEaseIn , which tells the CABasicAnimation to start out slow and then speed up.
The CABasicAnimation animScaleUp is similar to animScaleDown . The big difference is that the
fromValue and toValue are opposite. We also set the value for beginTime to 1 second in the
future. The idea here is that we want the animation animScaleDown to run for a second, making
the coin get small enough to vanish, and then we want the animation animScaleUp to run when
animScaleDown is done, scaling the coin back up. The trick will be to swap the images used by the
delegate to
animScaleDown , if we are working with coinViewA , because we need to be notified
self as
delegate to animScaleUp . The animations that have had their delegates set will call the task
when they are done, as shown in Listing 4-26.
CoinsController (animationDidStop:finished:)
- (void)animationDidStop:(CAAnimation *)theAnimation finished:(BOOL)flag{
if ([[theAnimation valueForKey:@"name"] isEqual:@"animScaleDown"]){
UIImage* imageA = [coinViewA image];
[coinViewA setImage:[coinViewB image]];
[coinViewB setImage:imageA];
} else if ([[theAnimation valueForKey:@"name"] isEqual:@"animScaleUp"]){
[self checkMatches];
[self spinCoinAt:firstSelectedCoin];
[self spinCoinAt:secondSelectedCoin];
} else if ([[theAnimation valueForKey:@"name"] isEqual:@"animateOffScreen"]){
[coinsGame randomizeRows: matchingRows];
[coinsGame randomizeCols: matchingCols];
[self updateCoinViews];
}
}
Here we can see the task animationDidStop:finished: . Notice that three animations call this task.
The first two if statements are for handling the animations described in Listing 4-25. When the
animScaleDown animation is done, we swap the UIImages used by UIImageViews to represent the two
selected coins.
When the animation animScaleUp is done, we want to check whether there are any matches. Calling
checkMatches does this. We also want to start the recently selected coins spinning again. The
implementation of checkMatches is shown in Listing 4-27.