ios - NSDate 比较总是返回 NSOrderedSame

Question

我对 NSDate 比较有疑问。我尝试了在谷歌搜索我的问题时发现的几种解决方案，但没有任何变化:我比较两个日期，我总是得到 NSOrderedSame 或 NSTimeIntervals = 0.0000 之间的差异；

我的代码是这样的:

NSDateFormatter *inputFormatter = [[NSDateFormatter alloc] init];
    [inputFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

    for (checklisteModel *updateRecord in updateArray) 
    {

        NSDate *serverDate = [inputFormatter dateFromString:updateRecord.last_update];

        NSString *lastUpdateFromLocalRecord = [self getLastUpdateForChecklisteItemWithID:updateRecord.checklisteID];
        NSDate *localDate = [inputFormatter dateFromString:lastUpdateFromLocalRecord];

        NSDateFormatter* fmt = [[NSDateFormatter alloc] init];
        NSLog(@"checkliste ID: %i",updateRecord.checklisteID);
        NSLog(@"server Date: ----- %@",[fmt stringFromDate:serverDate]);
        NSLog(@"local Date: ----- %@",lastUpdateFromLocalRecord);



        NSLog(@"difference of dates: %f",[serverDate timeIntervalSinceDate:localDate]);


        NSTimeInterval distanceBetweenDates = [serverDate timeIntervalSinceDate:localDate];
        double secondsInMinute = 60;
        NSInteger secondsBetweenDates = distanceBetweenDates / secondsInMinute;

        if (secondsBetweenDates == 0)
            NSLog(@"seconds between == 0");
        else if (secondsBetweenDates < 0)
            NSLog(@"seconds between < 0");
        else
            NSLog(@"seconds between > 0");



        //last_update on server is earlier than local
        if ([serverDate compare:localDate] == NSOrderedAscending) 
        {

            NSLog(@"Server data is earlier than local data");
            NSLog([NSString stringWithFormat:@"server data: %@, local data: %@",updateRecord.last_update,lastUpdateFromLocalRecord]);
        }
        // server data is later than local data
        else if ([serverDate compare:localDate] == NSOrderedDescending) 
        {

            NSLog(@"Server data is later than local data");
            NSLog([NSString stringWithFormat:@"server data: %@, local data: %@",updateRecord.last_update,lastUpdateFromLocalRecord]);
        }
        else 
        {
            NSLog(@"Server data and local data are the same");
        }
    }

我的部分调试显示了这一点:

checkliste ID: 21
server Date: ----- 
local Date: ----- 2012-10-29 10:13:46
difference of dates: 3810.000000
seconds between > 0
Server data is later than local data
server data: 2012-10-29 11:17:16, local data: 2012-10-29 10:13:46

Answer 1

NSLog(@"server Date: ----- %@",updateRecord.last_update);

您没有在此处记录 serverDate，因此正如 Hot Licks 所建议的，它很可能为 nil。在Objective-C中可以向nil发送消息，结果为0或nil。你认为 NSOrderedSame 的值(value)是什么？我敢打赌它是 0。

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

我注意到您的日期格式化程序的输入格式与您记录的内容不完全匹配，因此预期输入与您提供的内容之间的差异可能足以阻止格式化程序创建日期。尝试为 inputFormatter 的日期格式添加秒数。