在 NSDate中获得时间信息，年、月、星期、日、时、分和秒：
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSDate *now;
NSDateComponents *comps = [[NSDateComponents alloc] init];
NSInteger unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit |
NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
now=[NSDate date];
comps = [calendar components:unitFlags fromDate:now];
int year=[comps year];
int week = [comps weekday];
int month = [comps month];
int day = [comps day];
int hour = [comps hour];
int min = [comps minute];
int sec = [comps second];
NSDataToNSString方法：
-(NSString *)NSDateToNSTring:(NSDate *)nsDate{
//NSString *string = [nsDate descriptionWithCalendarFormat:@"%Y/%m/%d %H:%M:%S" timeZone:nil locale:nil];此方法为是有API如果要上传APP不要使用
NSDateFormatter *fmt = [[[NSDateFormatter alloc] init] autorelease];
[fmt setDateFormat:@"yyyy/MM/dd hh:mm:ss"];
NSString *string=[fmt stringFromDate:nsDate];
return string;
}