Circular progress bar with animation pause and resume

gistfile1.txt

#import "ViewController.h"

@interface ViewController (){

}
@end

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    [self registerNotifications];
   
}


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

-(void)deregisterNotifications {
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidEnterBackgroundNotification object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidBecomeActiveNotification object:nil];
}

- (void)registerNotifications {
    // Add observers to application state changes
    [[NSNotificationCenter defaultCenter]addObserver:self
                                            selector:@selector(applicationDidEnterBackground)
                                                name:UIApplicationDidEnterBackgroundNotification
                                              object:nil];
    
    [[NSNotificationCenter defaultCenter]addObserver:self
                                            selector:@selector(applicationDidBecomeActive)
                                                name:UIApplicationDidBecomeActiveNotification
                                              object:nil];
}

-(void)applicationDidEnterBackground{
    [self pauseLayer:self.progressBar.layer];
}

-(void)applicationDidBecomeActive{
    [self resumeLayer:self.progressBar.layer];
}

-(void)pauseLayer:(CALayer*)layer
{
    CFTimeInterval pausedTime = [layer convertTime:CACurrentMediaTime() fromLayer:nil];
    layer.speed = 0.0;
    layer.timeOffset = pausedTime;
}

-(void)resumeLayer:(CALayer*)layer
{
    CFTimeInterval pausedTime = [layer timeOffset];
    layer.speed = 1.0;
    layer.timeOffset = 0.0;
    layer.beginTime = 0.0;
    CFTimeInterval timeSincePause = [layer convertTime:CACurrentMediaTime() fromLayer:nil] - pausedTime;
    layer.beginTime = timeSincePause;
}


- (IBAction)StartProgressBar:(id)sender {
        [UIView animateWithDuration:60 animations:^{
            self.progressBar.value = 90;
        }];
}

@end