iOS 雪花效果

1.transform属性介绍

在OC中，通过transform属性可以修改对象的平移、缩放比例和旋转角度

常用的创建transform结构体方法分两大类

  （1） 创建“基于控件初始位置”的形变

　　CGAffineTransformMakeTranslation（平移）

　　CGAffineTransformMakeScale（缩放）

　　CGAffineTransformMakeRotation（旋转)

 （2） 创建“基于transform参数”的形变

　　CGAffineTransformTranslate

　　CGAffineTransformScale

　　CGAffineTransformRotate

 2. 代码实现

#import "ViewController.h"

#define degree2angle(angle)  ((angle) * M_PI / 180)

@interface ViewController ()

@property (nonatomic, strong) CADisplayLink *timer;
@property (nonatomic ,assign) long long steps;

@end
@implementation ViewController

- (CADisplayLink *)timer

{
    if (_timer == nil) {
        _timer = [CADisplayLink displayLinkWithTarget:self selector:@selector(update)];
    }
    return _timer;
}

- (void)loadView
{
    UIImageView *bg = [[UIImageView alloc]initWithFrame:[UIScreen mainScreen].bounds];
    bg.image = [UIImage imageNamed:@"snowbg.jpg"];
    bg.contentMode = UIViewContentModeScaleAspectFill;
    bg.userInteractionEnabled = YES;
    self.view = bg;

}

- (void)viewDidLoad {

    [super viewDidLoad];
    [self.timer addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
}

//点击的时候动画停止

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event

{
    [self stopTimer];

}


- (void)stopTimer

{
    [self.timer invalidate];
}

- (void)update

{
    _steps++;
    //执行5次添加一次
    if (_steps % 5 == 0) {
        [self snow];
    }
}

// 隐藏状态栏

- (BOOL)prefersStatusBarHidden

{
    return YES;
}

//方法一 用transform属性设置

/*

- (void)snow

{
    // 1.实例化一个雪花的图像视图
    UIImage *image = [UIImage imageNamed:@"雪花"];
    UIImageView *imageView = [[UIImageView alloc]initWithImage:image];

    // 0.1~0.4 随机在0.01~0.4缩放
    CGFloat scale = arc4random_uniform(40)/100.0 + 0.01;

    // 设置雪花缩放
    imageView.transform = CGAffineTransformMakeScale(scale, scale);
    CGSize winSize = self.view.bounds.size;

    // 2.添加到视图
    CGFloat x = arc4random_uniform(winSize.width);
    CGFloat y = -imageView.bounds.size.height * 0.5;
    imageView.center = CGPointMake(x, y);
    [self.view addSubview:imageView];

    

    // 3.动画下落
    [UIView animateWithDuration:10.0f animations:^{

        // 移动到终点位置
        CGFloat toX = arc4random_uniform(winSize.width);
        CGFloat toY = winSize.height + imageView.bounds.size.height * 0.5;
        imageView.center = CGPointMake(toX, toY);

        

        // 下过过程中,设置雪花360度随机旋转
        imageView.transform = CGAffineTransformRotate(imageView.transform, degree2angle(arc4random_uniform(360)));
        imageView.alpha = 0.3;

    } completion:^(BOOL finished) {
        [imageView removeFromSuperview];
    }];
}

*/

 

//方法二 用kvc设置

- (void)snow

{
    // 1.实例化一个雪花的图像视图

    // 整个视图的尺寸

    CGSize winSize = self.view.bounds.size;
    UIImage *image = [UIImage imageNamed:@"雪花"];

    // 2.添加到视图
    UIImageView *imageView = [[UIImageView alloc]initWithImage:image];
    CGFloat startX = arc4random_uniform(winSize.width);
    CGFloat startY = -imageView.bounds.size.height;
    imageView.center = CGPointMake(startX, startY);

    // 0.01~0.4 随机在0.01~0.4缩放
    CGFloat scale = arc4random_uniform(40)/100.0 + 0.01;
    [imageView.layer setValue:@(scale) forKeyPath:@"transform.scale"];
    [self.view addSubview:imageView];

    

    //3.动画下落
    [UIView animateWithDuration:10.0f animations:^{
        // 移动到终点位置
    CGFloat endX = arc4random_uniform(winSize.width);
    CGFloat endY = winSize.height + imageView.bounds.size.height;
    imageView.center = CGPointMake(endX, endY);

        // 下落的过程中旋转180度
    [imageView.layer setValue:@(M_PI) forKeyPath:@"transform.rotation"];

        // 不透明度为0.3
    [imageView.layer setValue:@(0.3) forKeyPath:@"opacity"];

    } completion:^(BOOL finished) {

        // 结束动画移除imageView
    [imageView removeFromSuperview]; 
    }]; 
}
@end