CAShapeLayer

    CAShapeLayer *arc;

    int radius = 100;
    arc = [CAShapeLayer layer];
    arc.path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(100, 50) radius:radius startAngle:-M_PI_2 endAngle:M_PI + M_PI_2 clockwise:YES].CGPath;
    arc.position = CGPointMake(CGRectGetMidX(self.view.frame)-radius,
                               CGRectGetMidY(self.view.frame)-radius);
    arc.cornerRadius = 100.0;
    arc.fillColor = [UIColor clearColor].CGColor;
    arc.strokeColor = [UIColor purpleColor].CGColor;
    arc.lineWidth = 6;
    
    [self.view.layer addSublayer:arc];
    
    // Animation of the progress bar
    CABasicAnimation *drawAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
    drawAnimation.duration            = 5.0; // "animate over 10 seconds or so.."
    drawAnimation.repeatCount         = 1.0;  // Animate only once..
    drawAnimation.removedOnCompletion = YES;   // Remain stroked after the animation..
    drawAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
    drawAnimation.toValue   = [NSNumber numberWithFloat:10.0f];
    drawAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];
    [arc addAnimation:drawAnimation forKey:@"drawCircleAnimation"];
    
    // Gradient of progress bar
    CAGradientLayer *gradientLayer = [CAGradientLayer layer];
    gradientLayer.frame = self.view.frame;
    gradientLayer.colors = @[(__bridge id)[UIColor redColor].CGColor,(__bridge id)[UIColor yellowColor].CGColor,(__bridge id)[UIColor purpleColor].CGColor ];
    gradientLayer.startPoint = CGPointMake(0,0.1);
    gradientLayer.endPoint = CGPointMake(0.5,0.2);
    [self.view.layer addSublayer:gradientLayer];
    gradientLayer.mask = arc;