``` @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;
}
```
