iphone - 为什么 NSDate 不能使用 < 或 > 进行比较？

Question

NSDate *date = [NSDate date];
NSDateFormatter *dateFormat = [[NSDateFormatter alloc]init];
[dateFormat setDateFormat:@"MM/dd/yyyy"];
NSLog([@"today is " stringByAppendingString:[dateFormat stringFromDate:date]]);
NSLog([@"firstBirthdayDate is " stringByAppendingString:[dateFormat stringFromDate:firstBirthdayDate]]);
NSLog([@"secondBirthdayDate is " stringByAppendingString:[dateFormat stringFromDate:secondBirthdayDate]]);
if ([firstBirthdayDate isEqualToDate:secondBirthdayDate])
    NSLog(@"First date is the same as second date");
if (firstBirthdayDate < date)
    NSLog(@"First date is earlier than today");
else
    NSLog(@"First date is later than today");

if (secondBirthdayDate < date)
    NSLog(@"Second date is earlier than today");

• 今天是 11/08/2012
• 第一个生日日期是 01/23/2012
• secondBirthdayDate 是 01/23/2012

这是我在日志中得到的内容:

First date is the same as second date

First date is later than today

Second date is earlier than today

我觉得我要疯了......

Answer 1

使用 if ([date1 isEqualToDate:date2])用于比较两个日期，否则您可以使用以下内容，

if ([date1 compare:date2] == NSOrderedSame)

if ([date1 compare:date2] == NSOrderedAscending)

if ([date1 compare:date2] == NSOrderedDescending)

> , <或 =仅用于比较非指针。基本上我的理解是，当您使用这些运算符时，它可能会比较内存地址而不是其中的值。所以你会得到意想不到的结果。

从逻辑上讲，它是这样工作的:

    if (obj1 > obj2) {
        return NSOrderedDescending;
    }

    if (obj1 < obj2) {
        return NSOrderedAscending;
    }

    if (obj1 == obj2) {
        return NSOrderedSame;
    }

您可以使用任何比较语句来比较日期。