比较日期大小是任何编程语言都会经常遇到的问题，再iOS编程中，通常用NSDate对象来存储一个时间（包括日期和时间、时区），而且 NSDate类提供了compare方法来进行时间的比较，但有时不想那么精确的知道两个日期的大小（默认会比较到秒），可以用下面的实现方法：

+(int)compareOneDay:(NSDate *)oneDay withAnotherDay:(NSDate *)anotherDay
{
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"dd-MM-yyyy"];
    NSString *oneDayStr = [dateFormatter stringFromDate:oneDay];
    NSString *anotherDayStr = [dateFormatter stringFromDate:anotherDay];
    NSDate *dateA = [dateFormatter dateFromString:oneDayStr];
    NSDate *dateB = [dateFormatter dateFromString:anotherDayStr];
    NSComparisonResult result = [dateA compare:dateB];
    NSLog(@"date1 : %@, date2 : %@", oneDay, anotherDay);
    if (result == NSOrderedDescending) {
        //NSLog(@"Date1  is in the future");
        return 1;
    }
    else if (result == NSOrderedAscending){
        //NSLog(@"Date1 is in the past");
        return -1;
    }
    //NSLog(@"Both dates are the same");
    return 0;
             
}