1、獲取當前時間

//獲取當前時間,時間格式yyyyMMddHHmmssSSS
 -(NSString * )getCurrentHourAndMinuteTime{
        NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
        // 設置想要的格式，hh與HH的區別:分別表示12小時制,24小時制
        [formatter setDateFormat:@"yyyyMMddHHmmssSSS"];
        NSDate *dateNow = [NSDate date];
      //把NSDate按formatter格式轉成NSString
        NSString *currentTime = [formatter stringFromDate:dateNow];
        return currentTime;
}

2、計算兩個時間點的時間差，精確到毫秒，時間格式yyyyMMddHHmmssSSS

//獲取兩個時間點的時間差，精確到毫秒
-(double )getTimeDifferenceWithStartTime:(NSString * )startTime andEndTime:(NSString *)endTime{
      NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
      [dateFormatter setDateFormat:@"yyyyMMddHHmmssSSS"];
      NSDate* startTimeData = [dateFormatter dateFromString:startTime];
      NSTimeInterval startTimeSp=[startTimeData timeIntervalSince1970]*1000;// *1000 是精確到毫秒，  不乘就是精確到秒
      NSDate* endTimeData = [dateFormatter dateFromString:endTime];
      NSTimeInterval endTimeSp=[endTimeData timeIntervalSince1970]*1000;
      double difference = (endTimeSp - startTimeSp);
      NSLog(@"開始時間：%@,結束時間：%@,兩個時間差為%lf秒",startTime,endTime, difference);
      return difference;
}

3、獲取日期date對應月的第一天日期

+ (NSString *)getMonthFirstDayWithDate:(NSDate *)date format:(NSDateFormatter *)myDateFormatter
{
    NSDate *newDate = date;
    double interval = 0;
    NSDate *firstDate = nil;
    NSCalendar *calendar = [NSCalendar currentCalendar];
    BOOL bl = [calendar rangeOfUnit:NSCalendarUnitMonth startDate:& firstDate interval:&interval forDate:newDate];
    if (bl) {
        NSString *firstString = [myDateFormatter stringFromDate: firstDate];
        return firstString;
    }
      return @"";
}

4、獲取日期date對應月的最后一天日期

+ (NSString *)getMonthLastDayWithDate:(NSDate *)date format:(NSDateFormatter *)myDateFormatter
{
    NSDate *newDate = date;
    double interval = 0;
    NSDate *firstDate = nil;
    NSDate *lastDate = nil;
    NSCalendar *calendar = [NSCalendar currentCalendar];
    BOOL bl = [calendar rangeOfUnit:NSCalendarUnitMonth startDate:& firstDate interval:&interval forDate:newDate];
    if (bl) {
        lastDate = [firstDate dateByAddingTimeInterval:interval - 1];
        NSString *lastString = [myDateFormatter stringFromDate: lastDate];
        return lastString;
    }
    return @"";
}

5、獲取對應日期是周幾

+ (NSInteger)getWeekDayFromDate:(NSDate *)date
{
    NSArray *tempWeek = @[@"7",@"1",@"2",@"3",@"4",@"5",@"6"];
    NSCalendar *calendar = [[NSCalendar alloc] 
initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSDateComponents *comps = [[NSDateComponents alloc] init];
    NSInteger unitFlags = NSCalendarUnitYear |NSCalendarUnitMonth | NSCalendarUnitDay |NSCalendarUnitWeekday | NSCalendarUnitHour |NSCalendarUnitMinute |NSCalendarUnitSecond;
    comps = [calendar components:unitFlags fromDate:date];
    // 1、2、3、4、5、6、7 分別對應 周日、周一、周二、周三、周四、周五、周六
    NSInteger week = [comps weekday];
    NSLog(@"---%ld",week);
    // 調整后 1 代表 周一
    return [tempWeek[week-1] integerValue] ;
}