Question

我有一个NSDate，我将其存入NSUserDefaults。

当我的应用程序运行此代码进行第二次传递时，我希望从NSUserDefaults中检索NSDate，但它总是为零。不知道为什么。

NSDate *mostRecentMentionDate = [dateFormatter dateFromString:mostRecentMentionMessageTimestamp];
NSDate *savedMentionDate = [[NSUserDefaults standardUserDefaults] objectForKey:@"mostRecentMentionDate"];

if (savedMentionDate == nil || [savedMentionDate isEqual:[NSNull null]]) {
    //There is no existing mention, so save the most recent one
    [[NSUserDefaults standardUserDefaults]setObject:mostRecentMentionDate forKey:@"mostRecentMentionDate"];
    [[NSUserDefaults standardUserDefaults] synchronize];
}

Answer 1

如果我使用此代码，它可以正常工作，我认为你的dateformater问题

NSDate *mostRecentMentionDate = [NSDate date];
NSDate *savedMentionDate = [[NSUserDefaults standardUserDefaults] objectForKey:@"mostRecentMentionDate"];

if (savedMentionDate == nil || [savedMentionDate isEqual:[NSNull null]]) {
  //There is no existing mention, so save the most recent one
  [[NSUserDefaults standardUserDefaults]setObject:mostRecentMentionDate forKey:@"mostRecentMentionDate"];
  [[NSUserDefaults standardUserDefaults] synchronize];
}

Answer 2

您确定要获得mostRecentMentionDate的有效对象吗？在从NSUserDefaults获取savedMentionDate之前将其放入NSLog，您可能遇到日期格式问题。

Answer 3

NSDate确认NSCoding协议。上面的代码应该工作。

试试这个 -

/

/ Create and store it
NSDate * date = [NSDate date];
NSData * dateData = [NSKeyedArchiver archivedDataWithRootObject:date];
[dateData writeToFile:@"/Some/path/to/file.dat" atomically:NO];

// Now bring it back
NSData * restoredDateData = [NSData dataWithContentsOfFile:@"/Some/path/to/file.dat"];
NSDate * restoredDate = [NSKeyedUnarchiver unarchiveObjectWithData:restoredDateData];

或者您可以将timeIntervalSinceReferenceDate值作为NSNumber（double）并将其保存到NSUserDefault以跟踪上一个日期。

从NSUserDefaults检索NSDate始终返回nil

3 个答案: