（5.20）step计数触发定时器--雪花效果

//  mainViewController.m
//  雪花
//
//  Created by pg
on 14-5-20.
//  Copyright (c) 2014年 mqd. All rights
reserved.
//

#import "mainViewController.h"

//时钟刷新步长
static
long step;

@interface mainViewController
()
//游戏时钟
@property(strong,nonatomic)CADisplayLink
*gameTime;
//雪花图像
@property(strong,nonatomic)UIImage
*snowImage;

@end

@implementation mainViewController
-
(void)viewDidLoad

{

    [super
viewDidLoad];
    //设置背景颜色
    [self.view
setBackgroundColor:[UIColor blackColor]];
  
 
    //实例化雪花
    self.snowImage =
[UIImage imageNamed:@"雪花.png"];
  
//设置时钟步长
     step = 0;
   
//1,实例化游戏时钟
    self.gameTime = [CADisplayLink
displayLinkWithTarget:self selector:@selector(step)];
   
//2，添加到主运行循环
    
    [self.gameTime
addToRunLoop:[NSRunLoop mainRunLoop]
forMode:NSDefaultRunLoopMode];

}
  
 
-(void)step{
    step++;
   
//每秒下十个
    if (step % 3 == 0)
{
       
//实例化uiimageview
        UIImageView
*imageView = [[UIImageView alloc]
initWithImage:self.snowImage];
      
 
           
//将uiimage添加到视图
        [self.view
addSubview:imageView];
       
//随机位子
        CGFloat x =
arc4random_uniform(320);
        CGFloat y
= - self.snowImage.size.height /
2;
        [imageView
setCenter:CGPointMake(x, y)];
     
 
      
 
      
 
       
//设置雪花大小
        CGFloat r =
arc4random_uniform(15) +10;
       
[imageView setBounds:CGRectMake(0, 0, r,
r)];
       
//实现uiview，动画结束后，删除uiimage
        [UIView
animateWithDuration:3.0f
animations:^{
          
 
          
 
        [imageView
setCenter:CGPointMake(arc4random_uniform(320), 450+arc4random_uniform(10))
];
          
 
           
//设置雪花旋转180度
           
[imageView
setTransform:CGAffineTransformMakeRotation(M_PI)];
          
 
           
//设置雪花透明
           
[imageView
setAlpha:0.3f];
          
 
        }completion:^(BOOL
finished)
{
           
[imageView removeFromSuperview];
       
}];
      
 
         }
  
 
        
}

@end