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() % 320);
    int endX = round(random() % 320);
    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 = 0.5;
    [self.view addSubview:flakeView];
    [UIView beginAnimations:nil context:(__bridge void *)(flakeView)];
    [UIView setAnimationDuration:5 * 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