ios draw circle with animation

http://stackoverflow.com/questions/7991086/iphone-core-animation-drawing-a-circle

// Set up the shape of the circle
int radius = 100;
CAShapeLayer *circle = [CAShapeLayer layer];
// Make a circular shape
circle.path = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(0, 0, 2.0*radius, 2.0*radius) 
                                         cornerRadius:radius].CGPath;
// Center the shape in self.view
circle.position = CGPointMake(CGRectGetMidX(self.view.frame)-radius, 
                              CGRectGetMidY(self.view.frame)-radius);

// Configure the apperence of the circle
circle.fillColor = [UIColor clearColor].CGColor;
circle.strokeColor = [UIColor blackColor].CGColor;
circle.lineWidth = 5;

// Add to parent layer
[self.view.layer addSublayer:circle];

// Configure animation
CABasicAnimation *drawAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
drawAnimation.duration            = 10.0; // "animate over 10 seconds or so.."
drawAnimation.repeatCount         = 1.0;  // Animate only once..

// Animate from no part of the stroke being drawn to the entire stroke being drawn
drawAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
drawAnimation.toValue   = [NSNumber numberWithFloat:1.0f];

// Experiment with timing to get the appearence to look the way you want
drawAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseIn];

// Add the animation to the circle
[circle addAnimation:drawAnimation forKey:@"drawCircleAnimation"];


http://stackoverflow.com/questions/21872610/animate-a-cashapelayer-to-draw-a-progress-circle

[UIBezierPath bezierPathWithArcCenter:arcCenter
                                                         radius:radius
                                                     startAngle:M_PI
                                                       endAngle:-M_PI
                                                      clockwise:YES];
实现类似qq加载效果