NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];BOOL datesAreEqual = [calendar isDate:firstDate equalToDate:secondDate toUnitGranularity:NSDayCalendarUnit];

#import <Foundation/Foundation.h>@interface NSCalendar (equalWithGranularity)- (BOOL)isDate:(NSDate *)date1 equalToDate:(NSDate *)date2 withGranularity:(NSCalendarUnit)granularity;@end

#import "NSCalendar+equalWithGranularity.h"@implementation NSCalendar (equalWithGranularity)- (BOOL)isDate:(NSDate *)date1 equalToDate:(NSDate *)date2 withGranularity:(NSCalendarUnit)granularity {if ([date1 isEqualToDate:date2]) {return YES;}int componentFlags = [self componentFlagsWithGranularity:granularity];date1 = [self dateFromDate:date1 withComponentFlags:componentFlags];date2 = [self dateFromDate:date2 withComponentFlags:componentFlags];return [date1 isEqualToDate:date2];}
- (int)componentFlagsWithGranularity:(NSCalendarUnit)granularity
{int componentFlags = 0;for (int i = 1<<1 ; i <= granularity ; i = i<<1) {componentFlags = componentFlags | i;}return componentFlags;}
- (NSDate *)dateFromDate:(NSDate *)date withComponentFlags:(int)componentFlags {NSDateComponents *components = [self components:componentFlags fromDate:date];return [self dateFromComponents:components];
}
@end

1 // 当前时间创建NSDate

NSDate *myDate = [NSDate date];NSLog(@"myDate = %@",myDate);2 //从现在开始的24小时

NSTimeInterval secondsPerDay = 24*60*60;NSDate *tomorrow = [NSDate dateWithTimeIntervalSinceNow:secondsPerDay];NSLog(@"myDate = %@",tomorrow);3//根据已有日期创建日期

NSTimeInterval secondsPerDay1 = 24*60*60;NSDate *now = [NSDate date];NSDate *yesterDay = [now addTimeInterval:-secondsPerDay1];NSLog(@"yesterDay = %@",yesterDay);4//比较日期

BOOL sameDate = [now isEqualToDate:yesterDay];NSLog(@"sameDate = %lu",sameDate);4.1//获取较早的日期

NSDate *earlierDate = [yesterDay earlierDate:now];NSLog(@"earlierDate = %@",earlierDate);4.2//较晚的日期

NSDate *laterDate = [yesterDay laterDate:now];NSLog(@"laterDate = %@",laterDate);//两个日期之间相隔多少秒

NSTimeInterval secondsBetweenDates= [yesterDay timeIntervalSinceDate:now];NSLog(@"secondsBetweenDates= %lf",secondsBetweenDates);//通过NSCALENDAR类来创建日期

NSDateComponents *comp = [[NSDateComponentsalloc]init];[comp setMonth:06];[comp setDay:01];[comp setYear:2001];NSCalendar *myCal = [[NSCalendaralloc]initWithCalendarIdentifier:NSGregorianCalendar];NSDate *myDate1 = [myCal dateFromComponents:comp];NSLog(@"myDate1 = %@",myDate1);//从已有日期获取日期

unsigned units = NSMonthCalendarUnit|NSDayCalendarUnit|NSYearCalendarUnit;NSDateComponents *comp1 = [myCal components:units fromDate:now];NSInteger month = [comp1 month];NSInteger year = [comp1 year];NSInteger day = [comp1 day];//NSDateFormatter实现日期的输出

NSDateFormatter *formatter = [[NSDateFormatteralloc]init];[formatter setDateStyle:NSDateFormatterFullStyle];//直接输出的话是机器码//或者是手动设置样式[formatter setDateFormat:@"yyyy-mm-dd"];

NSString *string = [formatter stringFromDate:now];NSLog(@"string = %@",string);NSLog(@"formater = %@",formatter);