六、雪花《苹果iOS实例编程入门教程》

该app为应用的功能为制作一场雪景

现版本 SDK 8.4 Xcode

纲要：
- UIImageView 的运用
- onTimer 代码运用
- onAnimation 代码运用

运行Xcode 选择 Create a new Xcode project ->Single View Application 命名 SnowFall

(1)  在xCode打开 ViewController.h 文件

(红色为所添加的代码)

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController{

UIImage *flakeImage;

}

@property(nonatomic,retain)UIImage *flakeImage;

-(void)onTimer;

-(void)onAnimationComplete:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context;

@end

(2)  在xCode打开 ViewController.m 文件

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

@synthesize flakeImage;

- (void)viewDidLoad {

[super viewDidLoad];

// Do any additional setup after loading the view, typically from a nib.

// RGB和alpha值的范围是0~1 Alpha透明度

// 把背景颜色设置为冷色

self.view.backgroundColor = [UIColor colorWithRed:0.5 green:0.5 blue:1.0 alpha:1.0];

// 导出雪花图片

flakeImage = [UIImage imageNamed:@"flake.png"];

// 每秒二十次的调用onTimer事件

[NSTimer scheduledTimerWithTimeInterval:(0.05) target:self selector:@selector(onTimer) userInfo:nil repeats:YES];

}

-(void)onTimer

{

//建立一个ImageView 放置雪花图片 flake image

UIImageView *flakeView = [[UIImageView alloc]initWithImage:flakeImage];

//随即生成参数坐标

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;

//设置雪花图片出现的坐标和透明度 即控制UIView的大小和该UIView在superview中的相对位置、透明度  基准为左上角

flakeView.frame = CGRectMake(startX, -100.0, 25.0*scale, 25.0*scale);

flakeView.alpha = 0.25;

//将flakeView添加进主视图

[self.view addSubview:flakeView];

//在 Objective-C 和 Core Foundation 对象之间进行转换时,就需要使用 Bridge cast（待详细研究）

[UIView beginAnimations:nil context:(__bridge void *)(flakeView)];

//动画时常

[UIView setAnimationDuration:5*speed];

//动画结束 图片位置

flakeView.frame = CGRectMake(endX, 500.0, 25.0*scale, 25.0*scale);

//*1*动画结束时调用 清理flakeView

[UIView setAnimationDidStopSelector:@selector(onAnimationComplete:finished:context:)];

[UIView setAnimationDelegate:self];

[UIView commitAnimations];

}

-(void)onAnimationComplete:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context{

UIImageView *flakeView = (__bridge UIImageView *)(context);

[flakeView removeFromSuperview];

//   NSLog(NSString stringWithFormat:@"[flakeView retainCount] = %d", [flakeView retainCount]]);

}

- (void)didReceiveMemoryWarning {

[super didReceiveMemoryWarning];

// Dispose of any resources that can be recreated.

}

@end

(3) 导入下面图片文件

下载下面图片，放入 SnowFall 文件夹内并命名为下面名称
flake.png

选择： File -> Save

最后在 xCode 选择 Build and then Running

(4)模拟器效果图

保留*1*处代码即动画结束后清理flake view效果为

不保留*1*处代码，效果为

本文源于网上博客教程，经过本人修改和测试。原blog地址 http://blog.sina.com.cn/s/blog_5fae23350100e1uk.html