Create Your Characters: Game Engine, Image Actors, and Behaviors - Beginning iOS6 Games Development - page 130

Updating updateScene
The task updateScene is also updated from the preceding chapter, as shown in Listing 6-4.
Listing 6-4. GameController.m (updateScene)
-(void)updateScene{
for (Actor* actor in actors){
[actor step:self];
}
for (Actor* actor in actors){
for (NSObject<Behavior>* behavoir in [actor behaviors]){
[behavoir applyToActor:actor In:self];
}
}
for (Actor* actor in actors){
[self updateViewForActor:actor];
}
[self doAddActors];
[self doRemoveActors];
stepNumber++;
}
In this listing, we iterate over all of the actors in the game three times. In the first loop, we call step :
on each actor, giving it a chance to apply any custom code. In the second loop, we apply each
Behavior associated with the actor. Behavior is a protocol that describes some shared behavior
among actors (this protocol is defined in Actor.h , shown later in Listing 6-9). In the third loop, we
update the UIView representing each actor by calling updateViewForActor :.
Because actors and behaviors are free to add or remove other actors and we don't want to modify
the NSMutableSet actors while we are iterating over that same collection, we have to add and
remove actors in two steps. To implement this two-step process, we store newly added actors in the
NSMutableSet actorsToBeAdded and then process each actor in that array in the task doAddActors .
We follow an identical pattern for actors to be removed, storing them in the NSMutableSet
actorsToBeRemoved and then processing them in the task doRemoveActors .
Calling doAddActors and doRemoveActors
The last step we take in updateScene is to call doAddActors and doRemoveActors , as shown in
Listing 6-5.
Listing 6-5. GameController.m (doAddActors and doRemoveActors)
-(void)doAddActors{
for (Actor* actor in actorsToBeAdded){
[actors addObject:actor];
UIView* view = [[actor representation] getViewForActor:actor In:self];
[view setFrame:CGRectMake(0, 0, 0, 0)];
[actorsView addSubview:view];