IOSdrawRect实现雪花飘落效果

#import <UIKit/UIKit.h>

@interface HHFSnowflakeFallingView : UIView

/**
 * 快速创建一个雪花飘落效果的view
 *
 * @param bgImageName 背景图片的名称
 * @param snowImageName 雪花图片的名称
 * @param frame  frame
 *
 * @return 实例化的 雪花飘落效果的view
 */

@property(nonatomic,strong) UIImageView *bgImageView;

@property(nonatomic,copy) NSString *snowImgName;

+ (instancetype) snowfladeFallingViewWithBackgroundImageName:(NSString *) bgImageName snowImageName:(NSString *)snowImageName initWithFrame:(CGRect)frame;
+ 
//开始下雪
- (void) beginShow;
@end

#import "HHFSnowflakeFallingView.h"

@implementation HHFSnowflakeFallingView
/**
 * <#Description#>
 *
 * @param bgImageName bgImageName 背景图片
 * @param snowImageName snowImageName 雪花图片
 * @param frame   frame 视图的位置和大小
 *
 * @return view  需要绘制的视图
 */
+ (instancetype) snowfladeFallingViewWithBackgroundImageName:(NSString *) bgImageName snowImageName:(NSString *)snowImageName initWithFrame:(CGRect)frame{

 HHFSnowflakeFallingView *view = [[HHFSnowflakeFallingView alloc] initWithFrame:frame];

 view.bgImageView.image = [UIImage imageNamed:bgImageName];
 view.snowImgName = snowImageName;
 return view;
}

- (instancetype)initWithFrame:(CGRect)frame
{
 self = [super initWithFrame:frame];
 if (self) {
  self.clipsToBounds = YES;

  //添加背景图片的imageview
  self.bgImageView = [[UIImageView alloc] init];
  self.bgImageView.frame = self.bounds;
  self.bgImageView.contentMode = UIViewContentModeScaleAspectFill;
  [self addSubview:self.bgImageView];
 }
 return self;
}

//开始下雪
- (void) beginShow{

 //启动定时器,使得一直调用setNeedsDisplay从而调用- (void) drawRect:(CGRect )rect
 //不得手动调用- (void) drawRect:(CGRect )rect
 CADisplayLink *link = [CADisplayLink displayLinkWithTarget:self selector:@selector(setNeedsDisplay)];
 //让定时器循环调用
 [link addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
}

- (void) drawRect:(CGRect)rect {

 //控制雪花最多的个数
 if (self.subviews.count >250) {
  return;
 }

 //雪花的宽度
 int width = arc4random() % 20;
 while (width < 5) {
  width = arc4random() % 20;
 }
 //雪花的速度
 int speed = arc4random() % 15;
 while (speed < 5) {
  speed = arc4random() % 15;
 }

 //雪花起点y
 int startY = - (arc4random() % 100);
 //雪花起点x
 int startX = arc4random() % (int) [UIScreen mainScreen].bounds.size.width;
 //雪花终点x
 int endX = arc4random() % (int) [UIScreen mainScreen].bounds.size.width;

 UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:self.snowImgName]];
  imageView.frame = CGRectMake(startX, startY, width, width);
 [self addSubview:imageView];


 //设置动画
 [UIView animateWithDuration:speed animations:^{
  //设置雪花最终的frame
  imageView.frame = CGRectMake(endX, [UIScreen mainScreen].bounds.size.height, width, width);
  //设置雪花的旋转
  imageView.transform = CGAffineTransformRotate(imageView.transform, M_PI);
  //设置雪花透明度,使得雪花快落地的时候就像快消失的一样
  imageView.alpha = 0.3;
 } completion:^(BOOL finished) {
  [imageView removeFromSuperview];
 }];


}
@end

#import "ViewController.h"
#import "HHFSnowflakeFallingView.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
 [super viewDidLoad];

 /**
  雪花效果最主要的思路就是在于循环产生带雪花图片的imageView, 产生的雪花的imageview的 x、y、宽、下落的速度都是随机的，这个可以用随机数来产生数据。
  */

 self.navigationItem.title = @"雪花飘落效果";

 //创建雪花飘落效果的view
 HHFSnowflakeFallingView *snowflakeFallingView = [HHFSnowflakeFallingView snowfladeFallingViewWithBackgroundImageName:@"snow_background" snowImageName:@"snow" initWithFrame:self.view.bounds];

 //开始下雪
 [snowflakeFallingView beginShow];

 [self.view addSubview:snowflakeFallingView];
}
@end