雪花飘落效果
- (void)viewDidLoad { [super viewDidLoad];flakeImage = [UIImage imageNamed:@"flake.png"];[NSTimer scheduledTimerWithTimeInterval:(0.05) target:self selector:@selector(play) userInfo:nil repeats:YES];}- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {return (interfaceOrientation == UIInterfaceOrientationLandscapeLeft);}- (void)play {UIImageView *flakeView = [[UIImageView alloc] initWithImage:flakeImage];int startX = round(random() % 1024);int endX = round(random() % 1024);double scale = 1 / round(random() % 100) + 1.0;double speed = 1 / round(random() % 100) + 1.0;flakeView.frame = CGRectMake(startX, -100.0, 25.0 * scale, 25.0 * scale);flakeView.alpha = 0.55;[self.view addSubview:flakeView];[UIView beginAnimations:nil context:flakeView];[UIView setAnimationDuration:5 * speed];flakeView.frame = CGRectMake(endX, 768.0, 25.0 * scale, 25.0 * scale);[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];[flakeView release];}?
示例图：
