UIView的Animation(十二)

使用UIView的Animation來實做一個下雪的動畫

1. 開啓一個專案

2. 加入一個雪花的圖片，需要一個背景為透明的雪花圖

3.在mainViewController.m加上程式碼

#import "mainViewController.h"

#define snowSize  25

@interface mainViewController ()
{
    UIImage* flakeImage;
}
@end

@implementation mainViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
   
    self.view.backgroundColor = [UIColor colorWithRed:0.5 green:0.5 blue:1.0 alpha:1.0];
   
    // load our flake image we will use the same image over and over
    flakeImage = [UIImage imageNamed:@"flake.png"];
   
    // start a timet that will fire 20 times per second
    [NSTimer scheduledTimerWithTimeInterval:(0.05) target:self selector:@selector(onTimer) userInfo:nil repeats:YES];

}


// Timer event is called whenever the timer fires
- (void)onTimer
{
    // build a view from our flake image
    UIImageView* flakeImageView = [[UIImageView alloc] initWithImage:flakeImage];
   
    // use the random() function to randomize up our flake attributes
    int startX = round(random() % 734);
    int endX = round(random() % 734);
    double scale = 1 / round(random() % 100) + 1.0;
    double speed = 1 / round(random() % 100) + 1.0;
   
    // set the flake start position
    flakeImageView.frame = CGRectMake(startX, -100.0, snowSize * scale, snowSize * scale);
    flakeImageView.alpha = 0.25;
   
    // put the flake in our main view
    [self.view addSubview:flakeImageView];
   
    [UIView beginAnimations:nil context:(void *)flakeImageView]; //針對雪花的動畫

   
    // set up how fast the flake will fall
    [UIView setAnimationDuration:10 * speed];
   
    // set the postion where flake will move to
    flakeImageView.frame = CGRectMake(endX, 880, snowSize * scale, snowSize * scale);
   
    // set a stop callback so we can cleanup the flake when it reaches the
    // end of its animation
    [UIView setAnimationDidStopSelector:@selector(onAnimationComplete:finished:context:)];
    [UIView setAnimationDelegate:self];
    [UIView commitAnimations];
   
}
- (void)onAnimationComplete:(NSString *)animationID finished:(NSNumber *)finished context:(void *)context {
   
    UIImageView *flakeImageView = (__bridge UIImageView *)(context);
    [flakeImageView removeFromSuperview];   
    // open the debug log and you will see that all flakes have a retain count
    // of 1 at this point so we know the release below will keep our memory
    // usage in check
    //NSLog([NSString stringWithFormat:@"[flakeView retainCount] = %d", [flakeImageView i ]]);
   
    //NSLog([NSString stringWithFormat:@"[flakeView retainCount] = %d", [flakeImageView re]]);
   
    //[flakeImageView release];
    flakeImageView = nil;
   
}


- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end
 

4.顯示結果