常用工具类

/*计算这个月有多少天*/
- (NSUInteger)numberOfDaysInCurrentMonth
{
    // 频繁调用 [NSCalendar currentCalendar] 可能存在性能问题
    return [[NSCalendar currentCalendar] rangeOfUnit:NSDayCalendarUnit inUnit:NSMonthCalendarUnit forDate:self].length;
}

//获取这个月有多少周
- (NSUInteger)numberOfWeeksInCurrentMonth
{
    NSUInteger weekday = [[self firstDayOfCurrentMonth] weeklyOrdinality];
    NSUInteger days = [self numberOfDaysInCurrentMonth];
    NSUInteger weeks = 0;
    
    if (weekday > 1) {
        weeks += 1, days -= (7 - weekday + 1);
    }
    
    weeks += days / 7;
    weeks += (days % 7 > 0) ? 1 : 0;
    
    return weeks;
}



/*计算这个月的第一天是礼拜几*/
- (NSUInteger)weeklyOrdinality
{
    return [[NSCalendar currentCalendar] ordinalityOfUnit:NSDayCalendarUnit inUnit:NSWeekCalendarUnit forDate:self];
}



//计算这个月最开始的一天
- (NSDate *)firstDayOfCurrentMonth
{
    NSDate *startDate = nil;
    BOOL ok = [[NSCalendar currentCalendar] rangeOfUnit:NSMonthCalendarUnit startDate:&startDate interval:NULL forDate:self];
    NSAssert1(ok, @"Failed to calculate the first day of the month based on %@", self);
    return startDate;
}


- (NSDate *)lastDayOfCurrentMonth
{
    NSCalendarUnit calendarUnit = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit;
    NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:calendarUnit fromDate:self];
    dateComponents.day = [self numberOfDaysInCurrentMonth];
    return [[NSCalendar currentCalendar] dateFromComponents:dateComponents];
}

//上一个月
- (NSDate *)dayInThePreviousMonth
{
    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.month = -1;
    return [[NSCalendar currentCalendar] dateByAddingComponents:dateComponents toDate:self options:0];
}

//下一个月
- (NSDate *)dayInTheFollowingMonth
{
    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.month = 1;
    return [[NSCalendar currentCalendar] dateByAddingComponents:dateComponents toDate:self options:0];
}


//获取当前日期之后的几个月
- (NSDate *)dayInTheFollowingMonth:(int)month
{
    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.month = month;
    return [[NSCalendar currentCalendar] dateByAddingComponents:dateComponents toDate:self options:0];
}

//获取当前日期之后的几个天
- (NSDate *)dayInTheFollowingDay:(int)day
{
    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.day = day;
    return [[NSCalendar currentCalendar] dateByAddingComponents:dateComponents toDate:self options:0];
}

后续慢慢更新。。。。。