IOS上怎样画出1像素的线

#define SINGLE_LINE_WIDTH (/[UIScreen mainScreen].scale)

#define SINGLE_LINE_ADJUST_OFFSET ((/[UIScreen mainScreen].scale)/)

- (void)viewDidLoad {

[super
viewDidLoad];

// Do any additional setup after loading the view, typically from a nib.

;

UIView *view = [[UIView
alloc] initWithFrame:CGRectMake(xPos -
SINGLE_LINE_ADJUST_OFFSET,
SINGLE_LINE_WIDTH)];

view.backgroundColor = [UIColor
blackColor];

[self.view
addSubview:view];

}