1、获取当前时间

//获取当前时间,时间格式yyyyMMddHHmmssSSS
-(NSString * )getCurrentHourAndMinuteTime{

    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];

    // 设置想要的格式，hh与HH的区别:分别表示12小时制,24小时制

    [formatter setDateFormat:@"yyyyMMddHHmmssSSS"];

    NSDate *dateNow = [NSDate date];

    //把NSDate按formatter格式转成NSString

    NSString *currentTime = [formatter stringFromDate:dateNow];

    return currentTime;

}

2、计算两个时间点的时间差，精确到毫秒，时间格式yyyyMMddHHmmssSSS

//获取两个时间点的时间差，精确到毫秒
-(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 是精确到毫秒，不乘就是精确到秒

    NSDate* endTimeData = [dateFormatter dateFromString:endTime];

    NSTimeInterval endTimeSp=[endTimeData timeIntervalSince1970]*1000;

    double difference = (endTimeSp - startTimeSp);

    NSLog(@"开始时间：%@,结束时间：%@,两个时间差为%lf秒",startTime,endTime, difference);

    return difference;

}

3、获取日期date对应月的第一天日期

+ (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、获取日期date对应月的最后一天日期

+ (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、获取对应日期是周几

+ (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 分别对应 周日、周一、周二、周三、周四、周五、周六

    NSInteger week = [comps weekday];

    NSLog(@"---%ld",week);

    // 调整后 1 代表 周一

    return [tempWeek[week-1] integerValue] ;
}