好吧，我想在没有 openGL 或 cocs2D 的情况下创建像 (snow) 这样的粒子，我发现这个示例代码被调用snowfall，在这个代码中有这个：
flakeImage = [UIImage imageNamed:@"flake.png"];
// start a timet that will fire 20 times per second
[NSTimer scheduledTimerWithTimeInterval:(0.5) target:self selector:@selector(onTimer) userInfo:nil repeats:YES];
}
// Timer event is called whenever the timer fires
- (void)onTimer
{
// build a view from our flake image
UIImageView* flakeView = [[UIImageView alloc] initWithImage:flakeImage];
// use the random() function to randomize up our flake attributes
int startX = round(random() % 320);
int endX = round(random() % 320);
double scale = 1 / round(random() % 100) + 1.0;
double speed = 1 / round(random() % 100) + 1.0;
// set the flake start position
flakeView.frame = CGRectMake(startX, -100.0, 5.0 * scale, 5.0 * scale);
flakeView.alpha = 0.25;
// put the flake in our main view
[self.view addSubview:flakeView];
[UIView beginAnimations:nil context:flakeView];
// set up how fast the flake will fall
[UIView setAnimationDuration:5 * speed];
// set the postion where flake will move to
flakeView.frame = CGRectMake(endX, 500.0, 5.0 * scale, 5.0 * scale);
// set a stop callback so we can cleanup the flake when it reaches the
// end of its animation
[UIView setAnimationDidStopSelector:@selector(onAnimationComplete:finished:context:)];
[UIView setAnimationDelegate:self];
[UIView commitAnimations]; }
- (void)onAnimationComplete:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
UIImageView *flakeView = context;
[flakeView removeFromSuperview];
// open the debug log and you will see that all flakes have a retain count
// of 1 at this point so we know the release below will keep our memory
// usage in check
NSLog([NSString stringWithFormat:@"[flakeView retainCount] = %d", [flakeView retainCount]]);
[flakeView release];
}
我想知道这段代码是否会损害性能或内存（可能是因为它使用了计时器）？如果这不是一个好主意，我听说我们可以在 iphone 上使用 CAReplicator 但 CAReplicatorDemo 仅适用于苹果文档上的 mac ：/对不起我的英语我是法国人：/