Create Your Characters: Game Engine, Image Actors, and Behaviors - Beginning iOS6 Games Development - page 153

if (stepsRemaining <= 0){
[gameController removeActor:anActor];
}
}
@end
In this implementation of the class ExpireAfterTime , the constructor expireAfter : simply creates a
new ExpireAfterTime object and sets the stepsRemaining property. The task applyToActor:In :
is called by a GameController for each step of the game. In this task, we decrement stepsRemaining
and update the delegate that the number of steps was updated. If stepsRemaining is zero or less,
we remove the actor from the GameController .
Before we add ExpireAfterTime to the Powerup object, we set the Powerup object as the delegate
ExpireAfterTime . This causes ExpireAfterTime to call stepsUpdated:In : on the Powerup object.
stepsUpdated:In : for the class Powerup .
Powerup.m (stepsUpdated:In:)
long stepsRemaining = [expire stepsRemaining];
if (stepsRemaining<60*5){
if (stepsRemaining % 25 == 0){
if (self.state == STATE_GLOW){
self.state = STATE_NO_GLOW;
} else {
self.state = STATE_GLOW;
}
}
}
}
In this listing, we check how many steps are remaining for the ExpireAfterTime object. If that value
is fewer than 300 steps (5 seconds at 60 frames per second), we want to apply our blinking logic. To
make the power-up blink, we swap the state of Powerup from STATE_GLOW to STATE_NO_GLOW, or
vice versa.
Changing the state is all that is required to change which image represents the Powerup actor
because (looking back at Listing 6-10) we know that setting the state of an actor sets its
needViewUpdated property to YES. Further, if an actor's needViewUpdated property is YES and that
actor is using an ImageRepresentation , that ImageRepresentation will fetch the correct image for the
actor in the task updateView:In : (as shown earlier in Listing 6-19).
Summary
In this chapter, we looked at our base game engine classes GameController and Actor and learned
how to use these classes to create a simple scene exercising our new actor, the power-up. We
looked at the protocol Behavior, which provides us with a framework for creating reusable bits of
game logic to be applied to our actors. We also consolidated the logic required to render an image-
based actor into the class ImageRepresentation . This also set the stage for vector-based actors,
which will be discussed in the following chapter.