//UIColor的延展
  //将color转换成RGB
extension UIColor {
    
    func r() -> CGFloat {
        
        return CGColorGetComponents(self.CGColor)[0];
    }
    
    func g() -> CGFloat {
        
        let count = CGColorGetNumberOfComponents(self.CGColor);
        if (count == 2) {
            return CGColorGetComponents(self.CGColor)[0];
        } else {
            return CGColorGetComponents(self.CGColor)[1];
        }
    }
    
    func b() -> CGFloat {
        
        let count = CGColorGetNumberOfComponents(self.CGColor);
        if (count == 2) {
            return CGColorGetComponents(self.CGColor)[0];
        } else {
            return CGColorGetComponents(self.CGColor)[2];
        }
    }
    
    func a() -> CGFloat {
        
        let count = CGColorGetNumberOfComponents(self.CGColor);
        return CGColorGetComponents(self.CGColor)[count - 1];
    }
}