The animation just run one time? - objective-c

Question

The problems is the animation just run one time then cannot repeat again. Do I need to add one more NSTimer in somewhere ?
Anything I missing ? Looking for help and advice. Thanks a lot !
And here is the code.
First, in ViewController.h & ViewController.m
#interface ViewController : UIViewController {
GameView* gameView;
}
- (void)viewDidLoad
{
[super viewDidLoad];
if(gameView == nil) {
gameView = [[GameView alloc] initWithFrame:CGRectMake(0, 0, 320, 480)];
gameView.backgroundColor = [UIColor clearColor];
}
[self.view addSubview:gameView];
[[AppEngine sharedInstance] addSnow:CGPointMake((random() % 320),(random() % -20))];
[[AppEngine sharedInstance] addSnow:CGPointMake((random() % 320),(random() % -20))];
[[AppEngine sharedInstance] addSnow:CGPointMake((random() % 320),(random() % -20))];
[[AppEngine sharedInstance] addSnow:CGPointMake((random() % 320),(random() % -20))];
[[AppEngine sharedInstance] addSnow:CGPointMake((random() % 320),(random() % -20))];
}
In the GameView.h & .m
#interface GameView : UIView <UIAccelerometerDelegate>{
CADisplayLink* displayLink;
}
-(void) timeStep;
- (id)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
displayLink = [CADisplayLink displayLinkWithTarget:self selector:#selector(timeStep)];
[displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
}
return self;
}
-(void) timeStep {
[[AppEngine sharedInstance] timeStep];
[self setNeedsDisplay];
}
- (void)drawRect:(CGRect)rect {
[[UIImage imageNamed:#"Christmas.jpg"] drawInRect:CGRectMake(0,0,320,480)]; // set the background image
CGContextRef context = UIGraphicsGetCurrentContext();
for(MySnow* snowObject in [AppEngine sharedInstance].snowObjectArray)
{
CGContextSaveGState(context);
CGContextTranslateCTM(context, snowObject.x, snowObject.y);
NSString *imagePath = [NSString stringWithFormat:#"snowflake0%d.png",snowObject.type];
[[UIImage imageNamed: imagePath] drawInRect:CGRectMake(-16,-16,32,32)];
CGContextRestoreGState(context);
}
}
Third, in the snow.h & m
#interface MySnow : NSObject
{
float x,y;
float vx, vy;
float rotSpeed;
float rotation;
int type;
}
#property (nonatomic) float x,y;
#property (nonatomic) float vx, vy, rotSpeed,rotation;
#property (nonatomic) int type;
-(id) initWithStartPoint:(CGPoint) startPoint withType:(int) type;
-(void) timeStep;
#implementation MySnow
#synthesize x,y,vx,vy,rotation,rotSpeed,type;
-(id) initWithStartPoint:(CGPoint) startPoint withType:(int) _type {
self = [super init];
if(self) {
x = startPoint.x;
y = startPoint.y;
vx = RANDOM_FLOAT() * 1 + 0.1;
vy = RANDOM_FLOAT() * 2 + 0.1;
type = _type;
}
return self;
}
-(void) timeStep {
y += vy;
}
Finally, in AppEngine.h & m
#interface AppEngine : NSObject {
NSMutableArray* snowObjectArray;
float ax, ay;
}
#property (readonly) NSMutableArray* snowObjectArray;
#property (nonatomic) float ax,ay;
+(AppEngine*) sharedInstance;
+(void) destoryInstance;
-(void) timeStep;
-(void) addSnow:(CGPoint) point;
static AppEngine* _sharedEngine;
#implementation AppEngine
#synthesize snowObjectArray;
#synthesize ax,ay;
+(AppEngine*) sharedInstance {
if(_sharedEngine == nil)
_sharedEngine = [[AppEngine alloc] init];
return _sharedEngine;
}
+(void) destoryInstance {
if(_sharedEngine != nil) {
_sharedEngine = nil;
}
}
-(id) init {
self = [super init];
if(self) {
snowObjectArray = [[NSMutableArray alloc] init];
}
return self;
}
-(void) addSnow:(CGPoint) point {
int type = (arc4random() % 9) + 1; // random snow image 01 to 09
MySnow* snowObject = [[MySnow alloc] initWithStartPoint:point withType:type];
[snowObjectArray addObject:snowObject];
}
-(void) timeStep {
NSMutableArray* removeArray = [NSMutableArray array];
for(MySnow* item in snowObjectArray) {
[item timeStep];
if(item.y > 400 || item.y < -100)
[removeArray addObject:item];
}
[snowObjectArray removeObjectsInArray:removeArray];
[removeArray removeAllObjects];
}

Answer 1

Is this your code? Can you explain how it starts the animation?
It looks to me like the AppEngine's timeStep method has code that specifically deletes each item in the snowObjectsArray once it reaches some boundary. However, if this is your code, why don't you understand what it does?
EDIT: OK, so this is from a lecture.
If you want the animation to continue, here's what I would do:
Take the last block of code from your viewDidLoad method (the code that creates and adds snow objects) and put it in a separate method. Make viewDidLoad call that method. Let's call the method makeItSnow.
Then, at the end of your AppEngine timeStep method, if the object count in snowObjectArray drops to 0, call makeItSnow.
That approach would make a set of snowflakes start at the top, fall down and disappear, and then another group of snowflakes start. If you want a continuous stream of snowflakes to fall, then change the timeStep method to count the number of snowflake objects it deletes, and at the end of the method add that many snowflakes back to the array. That would cause your program to add a new snowflake as each one disappears.
Yet another approach would be to add a repeating timer to AppEngine, and make that timer create another snowflake. That would keep adding snowflakes on a regular interval.