Create Your Characters: Game Engine, Image Actors, and Behaviors - Beginning iOS6 Games Development - page 152

Behavior: ExpireAfterTime
The class ExpireAfterTime is used by Powerup to remove it from the scene after a number of steps
have passed by. Before the power-up is removed, we want to make the power-up blink by changing
its state from glowing to not glowing. To support this second feature, we will want to have some sort
of communication between the ExpireAfterTime object and the actor it is acting on. Listing 6-25
shows the header of the class ExpireAfterTime .
Listing 6-25. ExpireAfterTime.h
#import <Foundation/Foundation.h>
#import "Actor.h"
@class ExpireAfterTime;
@protocol ExpireAfterTimeDelegate
-(void)stepsUpdated:(ExpireAfterTime*)expire In:(GameController*)controller;
@end
@interface ExpireAfterTime : NSObject <Behavior> {
}
@property (nonatomic) long stepsRemaining;
@property (nonatomic, assign) Actor<ExpireAfterTimeDelegate>* delegate;
+(id)expireAfter:(long)aNumberOfSteps;
@end
Here the class ExpireAfterTime conforms to the protocol Behavior, just like the class LinearMotion
does. ExpireAfterTime also defines a new protocol called ExpireAfterTimeDelegate that defines
the task stepsUpdated:In :, which will be called by the ExpireAfterTime on its delegate every time
applyToActor:In : is called, as shown in Listing 6-26.
Listing 6-26. ExpireAfterTime.m
#import "ExpireAfterTime.h"
#import "GameController.h"
@implementation ExpireAfterTime
@synthesize stepsRemaining;
@synthesize delegate;
+(id)expireAfter:(long)aNumberOfSteps {
ExpireAfterTime* expires = [ExpireAfterTime new];
[expires setStepsRemaining: aNumberOfSteps];
return expires;
}
-(void)applyToActor:(Actor*)anActor In:(GameController*)gameController{
stepsRemaining--;
[delegate stepsUpdated:self In:gameController];