ios判断星期几

- (NSString*)weekDayStr:(NSString *)format
{
    NSString *weekDayStr = nil;

  NSDateComponents *comps = [[NSDateComponents alloc] init];
  
  NSString *str = [self description];
  if (str.length >= 10) {
    NSString *nowString = [str substringToIndex:10];
    NSArray *array = [nowString componentsSeparatedByString:@"-"];
    if (array.count == 0) {
      array = [nowString componentsSeparatedByString:@"/"];
    }
    if (array.count >= 3) {
      int year = [[array objectAtIndex:0] integerValue];
      int month = [[array objectAtIndex:1] integerValue];
      int day = [[array objectAtIndex:2] integerValue];
      [comps setYear:year];
      [comps setMonth:month];
      [comps setDay:day];
    }
  }

  NSCalendar *gregorian = [[NSCalendar alloc]
                           initWithCalendarIdentifier:NSGregorianCalendar];
  NSDate *_date = [gregorian dateFromComponents:comps];
  NSDateComponents *weekdayComponents = [gregorian components:NSWeekdayCalendarUnit fromDate:_date];
  int week = [weekdayComponents weekday];
  week ++;
    switch (week) {
        case 1:
            weekDayStr = @"星期日";
            break;
        case 2:
            weekDayStr = @"星期一";
            break;
        case 3:
            weekDayStr = @"星期二";
            break;
        case 4:
            weekDayStr = @"星期三";
            break;
        case 5:
            weekDayStr = @"星期四";
            break;
        case 6:
            weekDayStr = @"星期五";
            break;
        case 7:
            weekDayStr = @"星期六";
            break;
        default:
        weekDayStr = @"";
            break;
    }
    return weekDayStr;
}