动画执行时调用的方法[UIView beginAnimations: context:];

@implementation ViewController


- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil

{

    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];

    if (self) {

        // Custom initialization

    }

    return self;

}


- (void)viewDidLoad

{

    [super viewDidLoad];

    UIImageView * iv = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 320, 460)];

    iv.image = [UIImage imageNamed:@"moji"];

    [self.view addSubview:iv];

    

    [UIView beginAnimations:nil context:nil];

    [UIView setAnimationDelegate:self];

    [UIView setAnimationWillStartSelector:@selector(animationDidStart:)];

    [UIView setAnimationDidStopSelector:@selector(animationDidStop:finished:)];

    [UIView setAnimationDelay:0.0f];

    [UIView setAnimationDuration:1.0f];

    

    iv.alpha = 0.0f;

    [UIView commitAnimations];

    //[iv release];


}


-(void)animationDidStart:(CAAnimation *)anim

{

    NSLog(@"animation is start ...");

}


-(void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag

{

    NSLog(@"animation is over ...");

}

@end

如上是规范的写法:

注意:

1、一定要写[UIView beginAnimations:nil context:nil];

2、一定要设置代理 因为后两者本质是协议方法

3、要设置选择器[UIView setAnimationWillStartSelector:@selector(animationDidStart:)];

有时候,你不设置选择器,只是设置了代理 如果你实现了 协议中的开始和停止方法,那么程序会执行stop方法,但是不会执行DidStart方法。

为了规范起见,要设置选择器。

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