scheduledTimerWithTimeInterval only triggers once when while Repeats is set to YES - objective-c

Question

I'm working through exercises in one of the Apress books. In the this chunk of code, an NSTimer object is created that is supposed to repeatedly trigger and call the gameloop function. I've set breakpoints in gameloop and it is only firing once. I'm trying to understand why. This seems fairly straightforward in terms of what it is supposed to do. Does anyone have guidance about what might be happening here?
#define RANDOM_SEED() srandom(time(NULL))
#define RANDOM_INT(__MIN__, __MAX__) ((__MIN__) + random() % ((__MAX__+1) - (__MIN__)))
#define kSteps 8
#define kSpeed 200
#define kFPS 20.0
#define kBounce 30
#define kDirForward 0
#define kDirBackward 1
#define kDirUp 2
#define kDirDown 3
static int kForward[] = {0,1,2,3,4,5,6,7};
static int kUpward[] = {8,9,10,11,12,13,14,15};
static int kDownward[] = {16,17,18,19,20,21,22,23};
static int kBackward[] = {24,24,25,26,27,28,29,30};
/** for mario.png
#define kSteps 6
static int kForward[] = {10,11,11,10,9,9};
static int kBackward[] = {22,23,23,22,21,21};
static int kUpward[] = {4,5,5,4,3,3};
static int kDownward[] = {16,17,17,16,15,15};
**/
- (id) initWithCoder: (NSCoder *) coder {
if (self = [super initWithCoder: coder]) {
test = [AtlasSprite fromFile: #"walk.png" withRows: 4 withColumns: 8];
test.angle = 0;
test.speed = kSpeed;
direction = kDirForward;
timer = [NSTimer scheduledTimerWithTimeInterval: 1.0/kFPS
target:self
selector:#selector(gameLoop)
userInfo:nil
repeats:YES];
self.backgroundColor = [UIColor whiteColor];
}
return self;
}
- (void) gameLoop
{
frame = (frame+1)%kSteps;
[test tic: 1.0/kFPS];
if (test.offScreen) {
RANDOM_SEED();
int toCenter = round(atan2(-test.y,-test.x)*180.0/3.141592);
if (toCenter < 0) toCenter += 360;
int bounce = (toCenter+RANDOM_INT(-kBounce,kBounce))%360;
if (bounce <= 60 || bounce >= 300) direction = kDirForward;
else if (bounce > 60 && bounce < 120) direction = kDirUp;
else if (bounce >= 120 && bounce <= 240) direction = kDirBackward;
else direction = kDirDown;
test.angle = bounce;
test.scale = 0.4+1.6*RANDOM_INT(0,10)/10.0;
while (test.offScreen) [test tic: 1.0/kFPS];
}
switch (direction) {
case kDirForward: test.frame = kForward[frame]; break;
case kDirBackward: test.frame = kBackward[frame]; break;
case kDirUp: test.frame = kUpward[frame]; break;
case kDirDown: test.frame = kDownward[frame]; break;
}
[self setNeedsDisplay];
}

Answer 1

Rich:
NSTimer is an autoreleased object. Because you are wanting it to repeat, you will need to retain the object. Try this:
timer = [[NSTimer scheduledTimerWithTimeInterval: 1.0/kFPS
target:self
selector:#selector(gameLoop)
userInfo:nil
repeats:YES] retain];
By retaining the timer you will need to make sure you release it when you no longer need it. Also make sure that you invalidate the timer when you are done with it.
I hope this resolves your issue.