Mask animation in iPhone

Hi,
Here is the sample code for "Mask Animation" in Objective C and iPhone/iPad/iPod.

#import <UIKit/UIKit.h>

typedef void (^animationCompletionBlock)(void);
#define kAnimationCompletionBlock @"animationCompletionBlock"

@interface ViewController : UIViewController
{
  BOOL animationInFlight;
  IBOutlet UIImageView *imageView;
}
@property (nonatomic) BOOL animationInFlight;

- (IBAction)MaskAnimation:(id)sender;


@end

#import <QuartzCore/QuartzCore.h>
#import "ViewController.h"


@interface ViewController ()

- (void) removePauseForLayer: (CALayer *) theLayer;
@end

@implementation ViewController


@synthesize animationInFlight;

#pragma mark - view lifecycle methods

- (void)viewDidLoad
{
  [super viewDidLoad];
}


//We only support portrait and portrait upside down orientations
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
  return UIInterfaceOrientationIsPortrait(interfaceOrientation);
}


- (void)viewDidUnload
{
  imageView = nil;
  [super viewDidUnload];
  // Release any retained subviews of the main view.
}

#pragma mark - Instance methods

- (IBAction)MaskAnimation:(id)sender;
{
    animationCompletionBlock theBlock;
    imageView.hidden = FALSE;//Show the image view
   
    //Create a shape layer that we will use as a mask for the  image view
    CAShapeLayer *maskLayer = [CAShapeLayer layer];
   
   
   
    CGFloat maskHeight = imageView.layer.bounds.size.height;
    CGFloat maskWidth = imageView.layer.bounds.size.width;
   
   
    CGPoint centerPoint;
    centerPoint = CGPointMake( maskWidth/2, maskHeight/2);
   
    //Make the radius of our arc large enough to reach into the corners of the image view.
    CGFloat radius = sqrtf(maskWidth * maskWidth + maskHeight * maskHeight)/2;
    //  CGFloat radius = MIN(maskWidth, maskHeight)/2;
   
    //Don't fill the path, but stroke it in black.
    maskLayer.fillColor = [[UIColor clearColor] CGColor];
    maskLayer.strokeColor = [[UIColor blackColor] CGColor];
   
    maskLayer.lineWidth = radius; //Make the line thick enough to completely fill the circle we're drawing
    //  maskLayer.lineWidth = 10; //Make the line thick enough to completely fill the circle we're drawing
   
    CGMutablePathRef arcPath = CGPathCreateMutable();
   
    //Move to the starting point of the arc so there is no initial line connecting to the arc
    CGPathMoveToPoint(arcPath, nil, centerPoint.x, centerPoint.y-radius/2);
   
    //Create an arc at 1/2 our circle radius, with a line thickess of the full circle radius
    CGPathAddArc(arcPath,
                 nil,
                 centerPoint.x,
                 centerPoint.y,
                 radius/2,
                 3*M_PI/2,
                 -M_PI/2,
                 NO);
   
    maskLayer.path = arcPath;
   
    //Start with an empty mask path (draw 0% of the arc)
    maskLayer.strokeEnd = 0.0;
   
   
    CFRelease(arcPath);
   
    //Install the mask layer into out image view's layer.
    imageView.layer.mask = maskLayer;
   
    //Set our mask layer's frame to the parent layer's bounds.
    imageView.layer.mask.frame = imageView.layer.bounds;
   
    //Create an animation that increases the stroke length to 1, then reverses it back to zero.
    CABasicAnimation *swipe = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
    swipe.duration = 2;
    swipe.delegate = self;
    [swipe setValue: theBlock forKey: kAnimationCompletionBlock];
   
    swipe.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    swipe.fillMode = kCAFillModeForwards;
    swipe.removedOnCompletion = NO;
    swipe.autoreverses = YES;
   
    swipe.toValue = [NSNumber numberWithFloat: 1.0];
   
    self.animationInFlight = TRUE;
  
    //Set up a completion block that will be called once the animation is completed.
    theBlock = ^void(void)
    {   
        imageView.layer.mask = nil;
        self.animationInFlight = FALSE;
        imageView.hidden = TRUE;
       
        if (self.view.layer.speed == 0)
            [self removePauseForLayer: self.view.layer];
    };
   
    /*
     Install the completion block in the animation using the key kAnimationCompletionBlock
     The completion block will be run by in the animation's animationDidStop:finished delegate method.
     This approach doesn't work for animations that are part of a group, unfortunately, since an animation's
     delegate methods don't get called when the animation is part of an animation group
     */
   
    [swipe setValue: theBlock forKey: kAnimationCompletionBlock];
   
    [maskLayer addAnimation: swipe forKey: @"strokeEnd"];
   
}


- (void) removePauseForLayer: (CALayer *) theLayer;
{
    theLayer.speed = 1.0;
    theLayer.timeOffset = 0.0;
    theLayer.beginTime = 0.0;
}

#pragma mark - CAAnimation delegate methods

- (void)animationDidStop:(CAAnimation *)theAnimation finished:(BOOL)flag
{
  animationCompletionBlock theBlock = [theAnimation valueForKey: kAnimationCompletionBlock];
  if (theBlock)
    theBlock();
}


@end