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

// Set up the shape of the circleint radius = 100;CAShapeLayer *circle = [CAShapeLayer layer];// Make a circular shapecircle.path = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(0, 0, 2.0*radius, 2.0*radius)                                          cornerRadius:radius].CGPath;// Center the shape in self.viewcircle.position = CGPointMake(CGRectGetMidX(self.view.frame)-radius,                               CGRectGetMidY(self.view.frame)-radius);// Configure the apperence of the circlecircle.fillColor = [UIColor clearColor].CGColor;circle.strokeColor = [UIColor blackColor].CGColor;circle.lineWidth = 5;// Add to parent layer[self.view.layer addSublayer:circle];// Configure animationCABasicAnimation *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 drawndrawAnimation.fromValue = [NSNumber numberWithFloat:0.0f];drawAnimation.toValue   = [NSNumber numberWithFloat:1.0f];// Experiment with timing to get the appearence to look the way you wantdrawAnimation.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