判断系统是12小时制还是24小时制

//获取系统是24小时制或者12小时制
NSString *formatStringForHours = [NSDateFormatter dateFormatFromTemplate:@"j" options:0 locale:[NSLocale currentLocale]];
NSRange containsA = [formatStringForHours rangeOfString:@"a"];
BOOL hasAMPM = containsA.location != NSNotFound;
//hasAMPM==TURE为12小时制，否则为24小时制