iOS7 custom leftBarButtonItem 偏移问题

- (void)createNavigationLeftBarB uttonItemWithCustomView:(UIButton *)button

{

      UIBarButtonItem *buttonItem = [[UIBarButtonItem alloc] initWithCustomView:button];

      if ([[[[UIDevice currentDevice] systemVersion] substringToIndex:1] intValue]>=7) {

            UIBarButtonItem *negativeSpacer = [[UIBarButtonItem alloc]initWithBarButtonSystemI tem:UIBarButtonSystemItemFix edSpace target:nil action:nil];

            negativeSpacer.width = -10;

            self.navigationItem.leftBarButtonItems = @[negativeSpacer, buttonItem];

      }else{

            self.navigationItem.leftBarButtonItem = buttonItem;

      }

}