比较2个时间点 哪个更早

比较2个时间点 哪个更早

- (NSInteger)compareDate:(NSString*)aDate withDate:(NSString*)bDate{

  NSDateFormatter *dateformater = [[NSDateFormatter alloc] init];
  [dateformater setDateFormat:@"yyyy-MM-dd"];

  NSDate*dta = [[NSDate alloc]init];
  NSDate*dtb = [[NSDate alloc]init];

  dta = [dateformater dateFromString:aDate];
  dtb = [dateformater dateFromString:bDate];
  NSComparisonResult result = [dta compare:dtb];

  if (result == NSOrderedDescending) {
      return 1;
  } else if(result == NSOrderedAscending) {
      return -1;
  } else {
      //刚好时间一样.
      return 0;
  }
}