知道这些，轻松写出日历控件

日历demo链接https://github.com/zhangxianhongx/Cleander
//得到date中是第几天

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

//得到date中时第几月

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

//得到date中是哪一年

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

//计算上一个月的date

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

//pragma makr 计算下一个月的date

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

//获取date中月份的第一天对应星期几

- (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;
}

//获取date中日期对应的星期 0星期六 1星期天 2星期一 3星期二 4星期三 5星期四 6星期五

- (NSInteger)getWeekWithDate:(NSDate *)date{

NSInteger weekDay = [self firstWeekdayInThisMonth:date];
NSInteger cureentDay = [self day:date];

//当前日期
NSInteger currentWeek = (cureentDay%7 + weekDay)%7;
return currentWeek;

}

//得到date中每月有多少天

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