// 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
（5.20）step计数触发定时器--雪花效果,布布扣,bubuko.com
原文：http://www.cnblogs.com/modingding/p/3740191.html