畫圈

 CAShapeLayer *circle = [CAShapeLayer layer];
    
    [circle setPath:[[UIBezierPath bezierPathWithOvalInRect:CGRectMake(100, 100, 150, 150)] CGPath]];
    
    [circle setStrokeColor:[[UIColor blueColor] CGColor]];

    [circle setFillColor:[[UIColor clearColor] CGColor]];
    
    [[self.view layer] addSublayer:circle];