将字符串分解为数组

    NSDate *date = [NSDate dateWithTimeIntervalSinceNow:60*60*24*self.index];
    //    NSLog(@"--index:%zd",self.index);
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
    formatter.dateFormat  = @"yyyy-MM-dd";
    //    formatter.dateFormat =  [date getDayOfWeekShortString];
    NSString *dateStr = [formatter stringFromDate:date];
    //    NSLog(@"%@",dateStr);
    return [dateStr componentsSeparatedByString:@"-"];//字符串分离成数组