画1像素的线

#define SINGLE_LINE_WIDTH           (1 / [UIScreen mainScreen].scale)

#define SINGLE_LINE_ADJUST_OFFSET   ((1 / [UIScreen mainScreen].scale) /2)

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {

    [superviewDidLoad];

    NSLog(@"%f",   [[UIScreenmainScreen]scale]);

UIView *lineview = [[UIViewalloc] initWithFrame:CGRectMake(10-SINGLE_LINE_ADJUST_OFFSET, 100, SINGLE_LINE_WIDTH,200)];

    lineview.backgroundColor=[UIColorredColor];

    [self.viewaddSubview:lineview];

}