iOS 动画绘制圆形

    @interface ViewController () {  
        CAShapeLayer *shapeLayer;  
        NSTimer *timer;  
    }  
      
    @end  
      
    @implementation ViewController  
      
    - (void)viewDidLoad {  
        [super viewDidLoad];  
          
        //第一步，通过UIBezierPath设置圆形的矢量路径  
        UIBezierPath *circle = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, 200, 200)];  
          
        //第二步，用CAShapeLayer沿着第一步的路径画一个完整的环（颜色灰色，起始点0，终结点1）  
        CAShapeLayer *bgLayer = [CAShapeLayer layer];  
        bgLayer.frame = CGRectMake(0, 0, 200, 200);//设置Frame  
        bgLayer.position = self.view.center;//居中显示  
        bgLayer.fillColor = [UIColor clearColor].CGColor;//填充颜色=透明色  
        bgLayer.lineWidth = 2.f;//线条大小  
        bgLayer.strokeColor = [UIColor grayColor].CGColor;//线条颜色  
        bgLayer.strokeStart = 0.f;//路径开始位置  
        bgLayer.strokeEnd = 1.f;//路径结束位置  
        bgLayer.path = circle.CGPath;//设置bgLayer的绘制路径为circle的路径  
        [self.view.layer addSublayer:bgLayer];//添加到屏幕上  
          
        //第三步，用CAShapeLayer沿着第一步的路径画一个红色的环形进度条，但是起始点=终结点=0，所以开始不可见  
        shapeLayer = [CAShapeLayer layer];  
        shapeLayer.frame = CGRectMake(0, 0, 200, 200);  
        shapeLayer.position = self.view.center;  
        shapeLayer.fillColor = [UIColor clearColor].CGColor;  
        shapeLayer.lineWidth = 2.f;  
        shapeLayer.strokeColor = [UIColor redColor].CGColor;  
        shapeLayer.strokeStart = 0;  
        shapeLayer.strokeEnd = 0;  
        shapeLayer.path = circle.CGPath;  
        [self.view.layer addSublayer:shapeLayer];  
          
        //第四步，用一个定时器进行测试，每一秒，进度加10%  
        timer = [NSTimer scheduledTimerWithTimeInterval:1.f target:self selector:@selector(animate) userInfo:nil repeats:YES];  
    }  
      
    - (void)animate {  
        shapeLayer.strokeEnd += 0.1;  
    }