http://blog.csdn.net/reylen/article/details/8560128

创建当前时间

NSDate *date = [NSDate date];  

从现在开始的24小时

        NSTimeInterval a_day = **;

        NSDate *tomorrow = [NSDate dateWithTimeIntervalSinceNow:a_day];

根据已有日期创建日期

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NSTimeInterval a_day = **;

NSDate *date = [NSDate date];

NSDate *tomorrow = [date addTimeInterval: date];

日期比较

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      BOOL isEqual = [date isEqualToDate:tomorrow];

f(isEqual){

NSLog(@"equal");  

//获取较早的日期

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NSDate *earlier_date = [tomorrow earlierDate:date];

  NSLog(@"earlierDate  = %@",earlierDate);  

//较晚的日期

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NSDate *laterDate = [tomorrow laterDate:date];

NSLog(@"laterDate  = %@",laterDate);  

//两个日期之间相隔多少秒

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NSTimeInterval secondsInterval= [date timeIntervalSinceDate:tomorrow];

NSLog(@"secondsInterval=  %lf",secondsInterval); 

 //通过NSCalendar类来创建日期

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NSDateComponents *comps = [[NSDateComponentsalloc]init];

[comps setMonth:];

[comps setDay:];

[comps setYear:];

NSCalendar *calendar = [[NSCalendaralloc]initWithCalendarIdentifier:NSGregorianCalendar];

NSDate *date = [calendar dateFromComponents:comps]; 

 //从已有日期获取日期

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unsigned units  = NSMonthCalendarUnit|NSDayCalendarUnit|NSYearCalendarUnit;

NSDateComponents *_comps = [calendar components:units fromDate:date];

NSInteger month = [_comps month];

NSInteger year = [_comps year];

NSInteger day = [_comps 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 *dateString = [formatter stringFromDate:date];

NSLog(@"dateString = %@",dateString);

NSLog(@"formater = %@",formatter);  

//获取日期格式对象

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- (NSDateFormatter *)getDateFormatter {

    if (dateFormatter == nil) {

    dateFormatter = [[NSDateFormatter alloc] init];

    [dateFormatter setDateStyle:NSDateFormatterMediumStyle];

    [dateFormatter setTimeStyle:NSDateFormatterNoStyle];

    }

    return dateFormatter;

}  

-(int)compareDate:(NSString*)date01 withDate:(NSString*)date02{

    int ci;

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

    [df setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

    NSDate *dt1 = [[NSDate alloc] init];

    NSDate *dt2 = [[NSDate alloc] init];

    dt1 = [df dateFromString:date01];

    dt2 = [df dateFromString:date02];

    NSComparisonResult result = [dt1 compare:dt2];

    switch (result)

    {

        //date02比date01大

        case NSOrderedAscending: ci=; break;

        //date02比date01小

        case NSOrderedDescending: ci=-; break;

        //date02=date01

        case NSOrderedSame: ci=; break;

        default: NSLog(@"erorr dates %@, %@", dt2, dt1); break;

    }

    return ci;

}