如何比较两个NSDates：哪个更近？ [英] How to compare two NSDates: Which is more recent?

问题描述

我想实现一个dropBox同步，需要比较两个文件的日期。一个是我的dropBox帐户，一个是在我的iPhone。

I am trying to achieve a dropBox sync and need to compare the dates of two files. One is on my dropBox account and one is on my iPhone.

我想出了以下情况，但我得到了意想不到的结果。我想我在做这些事情从根本上错误的比较两个日期。我只是使用><运算符，但我想这不是好，因为我比较两个NSDate字符串。我们去：

I came up with the following, but I get unexpected results. I guess I'm doing something fundamentally wrong when comparing the two dates. I simply used the > < operators, but I guess this is no good as I am comparing two NSDate strings. Here we go:

NSLog(@"dB...lastModified: %@", dbObject.lastModifiedDate); 
NSLog(@"iP...lastModified: %@", [self getDateOfLocalFile:@"NoteBook.txt"]);

if ([dbObject lastModifiedDate] < [self getDateOfLocalFile:@"NoteBook.txt"]) {
    NSLog(@"...db is more up-to-date. Download in progress...");
    [self DBdownload:@"NoteBook.txt"];
    NSLog(@"Download complete.");
} else {
    NSLog(@"...iP is more up-to-date. Upload in progress...");
    [self DBupload:@"NoteBook.txt"];
    NSLog(@"Upload complete.");
}

这给出了以下输出>

This gave me the following (random & wrong) output:

2011-05-11 14:20:54.413 NotePage[6918:207] dB...lastModified: 2011-05-11 13:18:25 +0000
2011-05-11 14:20:54.414 NotePage[6918:207] iP...lastModified: 2011-05-11 13:20:48 +0000
2011-05-11 14:20:54.415 NotePage[6918:207] ...db is more up-to-date.

或这个正确的：

2011-05-11 14:20:25.097 NotePage[6903:207] dB...lastModified: 2011-05-11 13:18:25 +0000
2011-05-11 14:20:25.098 NotePage[6903:207] iP...lastModified: 2011-05-11 13:19:45 +0000
2011-05-11 14:20:25.099 NotePage[6903:207] ...iP is more up-to-date.

推荐答案

让我们假设两个日期：

NSDate *date1;
NSDate *date2;

然后，以下比较将告诉哪个是早/晚/相同：

Then the following comparison will tell which is earlier/later/same:

if ([date1 compare:date2] == NSOrderedDescending) {
    NSLog(@"date1 is later than date2");
} else if ([date1 compare:date2] == NSOrderedAscending) {
    NSLog(@"date1 is earlier than date2");
} else {
    NSLog(@"dates are the same");
}

请参阅 NSDate类文档。

您可以在这里参考NSDate的StackOverflow文档： NSDate

You can refer the StackOverflow Documenation of NSDate here: NSDate

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