NSDate 时间比较...等

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;
}  

时间比较

-(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;
}