iOS飘雪的动画小demo

 ViewController.h

 #import <UIKit/UIKit.h>

 @interface ViewController : UIViewController{
     UIImage* flakeImage;
 }
 - (void)onTimer;
 @end

 ViewController.m

 #import "ViewController.h"

 @interface ViewController ()

 @end

 @implementation ViewController

 - (void)viewDidLoad
 {
     [super viewDidLoad];
     self.view.backgroundColor = [UIColor colorWithRed:0.5 green:0.5 blue:1.0 alpha:1.0];
     flakeImage = [UIImage imageNamed:@"2.png"];
     [NSTimer scheduledTimerWithTimeInterval:(0.05) target:self selector:@selector(onTimer) userInfo:nil repeats:YES];
 }
 - (void)onTimer
 {
     //创建图像视图对象
     UIImageView* flakeView = [[UIImageView alloc] initWithImage:flakeImage];

     int startX = round(random() % );
     int endX = round(random() % );
     double scale =  / round(random() % ) + 1.0;
     double speed =  / round(random() % ) + 1.0;
     flakeView.frame = CGRectMake(startX, -100.0, 25.0 * scale, 25.0 * scale);
     flakeView.alpha = 0.5;
     [self.view addSubview:flakeView];
     [UIView beginAnimations:nil context:(__bridge void *)(flakeView)];
     [UIView setAnimationDuration: * speed];
     flakeView.frame = CGRectMake(endX, 540.0, 25.0 * scale, 25.0 * scale);
     [UIView commitAnimations];

 }

 - (void)didReceiveMemoryWarning
 {
     [super didReceiveMemoryWarning];
     // Dispose of any resources that can be recreated.
 }

图片素材，通过Main.storyboard设置背景图片