NSDate的几个方法（记录一下）

1、获取日

- (NSInteger)day:(NSDate *)date{
    NSDateComponents *components = [[NSCalendar currentCalendar] components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay) fromDate:date];
    return [components day];
}

2、获取月

- (NSInteger)month:(NSDate *)date{
    NSDateComponents *components = [[NSCalendar currentCalendar] components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay) fromDate:date];
    return [components month];
}

3、获取年

- (NSInteger)year:(NSDate *)date{
    NSDateComponents *components = [[NSCalendar currentCalendar] components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay) fromDate:date];
    return [components year];
}

4、获取今天是周几

- (NSInteger)week:(NSDate *)date{
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSInteger unitFlags = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitWeekday | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
    NSDateComponents *comps = [calendar components:unitFlags fromDate:date];
    return [comps weekday];
}

5、获取本月总天数

- (NSInteger)totaldaysInThisMonth:(NSDate *)date{
    NSRange totaldaysInMonth = [[NSCalendar currentCalendar] rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:date];
    return totaldaysInMonth.length;
}

6、获取本月第一天是周几

- (NSInteger)firstWeekdayInThisMonth:(NSDate *)date{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    [calendar setFirstWeekday:1];//1.Sun. 2.Mon. 3.Thes. 4.Wed. 5.Thur. 6.Fri. 7.Sat.
    NSDateComponents *comp = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay) fromDate:date];
    [comp setDay:1];
    NSDate *firstDayOfMonthDate = [calendar dateFromComponents:comp];
    NSUInteger firstWeekday = [calendar ordinalityOfUnit:NSCalendarUnitWeekday inUnit:NSCalendarUnitWeekOfMonth forDate:firstDayOfMonthDate];
    return firstWeekday - 1;
}

7、获取上个月第一天

- (NSDate*)lastMonth:(NSDate *)date{
    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.month = -1;
    NSDate *newDate = [[NSCalendar currentCalendar] dateByAddingComponents:dateComponents toDate:date options:0];
    return newDate;
}

8、获取下个月第一天

- (NSDate*)nextMonth:(NSDate *)date{
    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.month = +1;
    NSDate *newDate = [[NSCalendar currentCalendar] dateByAddingComponents:dateComponents toDate:date options:0];
    return newDate;
}

9、获取明天

- (NSDate*)nextDay:(NSDate *)date{
    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.day = +1;
    NSDate *newDate = [[NSCalendar currentCalendar] dateByAddingComponents:dateComponents toDate:date options:0];
    return newDate;
}

10、获取昨天

- (NSDate*)lastDay:(NSDate *)date{
    NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
    dateComponents.day = -1;
    NSDate *newDate = [[NSCalendar currentCalendar] dateByAddingComponents:dateComponents toDate:date options:0];
    return newDate;
}

自己用的：获取本月共跨几周

- (NSInteger)weekNumThisMonth:(NSInteger)days firstWeekDays:(NSInteger)firstWeek{
    
    NSInteger num = (days-firstWeek)/7;
    if ((days-firstWeek)%7) {
        num ++;
    }
    num++;
    NSLog(@"%ld",(long)num);
    return num;
    
}