NSUserDefaults 在使用应用程序时保存并重新加载，但在应用程序重新启动时重置

Question

我有一种方法可以在特定日期第一次向用户发送消息时增加计数器。代码如下：

//here we decide if to increment it or not
-(BOOL)canIncrementCountForUser: (NSString *)user {

    //erase the dictionary if it's a new day
    [self flushDictionaryIfNeeded];

    //load up a dictionary
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    NSMutableDictionary *dictionary = [defaults objectForKey:@"uniqueSentToday"];

    NSLog(@"%@", [dictionary allKeys]);

    //if empty it's a yes
    if([dictionary count]==0){
        NSLog(@"empty dictionary");
        NSLog(@"First message for %@ today!",user);
        NSDate *now = [NSDate date];
        [dictionary setObject:now forKey:user]; //do I need to set it back again?
        [defaults synchronize];
        return YES;

    }

    //if it's not empty it's only a yes if the key doesn't exist
    else {

        //not in dict so unique
        if(![dictionary objectForKey:user]){
            NSLog(@"First message for %@ today!",user);
            NSDate *now = [NSDate date];
            [dictionary setObject:now forKey:user]; //do I need to set it back again?
            [defaults synchronize];
            return YES;

        }


        else {

            NSLog(@"Already messaged %@ today!",user);
            return NO;



        }




    }


}

-(void)flushDictionaryIfNeeded{

    //set dictionary
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    NSMutableDictionary *dictionary = [defaults objectForKey:@"uniqueSentToday"];

    if([dictionary count]>0) {

        //get any date
        NSDate *aDate = nil;
        NSArray *values = [dictionary allValues];
        aDate = [values objectAtIndex:0];

        NSDateComponents *otherDay = [[NSCalendar currentCalendar] components:NSCalendarUnitEra|NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay fromDate:aDate];
        NSDateComponents *today = [[NSCalendar currentCalendar] components:NSCalendarUnitEra|NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay fromDate:[NSDate date]];
        if([today day] == [otherDay day] &&
           [today month] == [otherDay month] &&
           [today year] == [otherDay year] &&
           [today era] == [otherDay era]) {

            NSLog(@"Don't flush");
        }

        else {

            NSLog(@"It's a new day! erase dictionary!");
            [dictionary removeAllObjects];
            [defaults synchronize];

        }

    }

}

如果向用户发送消息，将创建一个 NSDate 对象，并以用户的用户名作为键。如果密钥不存在，则可以递增计数器并添加密钥，如果它确实存在，则方法 returns false。如果是新的一天，我还有一种方法可以删除所有内容。代码一切正常，当程序正在使用时，NSMutableDictionary 似乎被保存到应用程序中，但是当我重新启动应用程序时，字典将为空。有人可以告诉我为什么会发生这种情况吗？谢谢

Answer 1

您修改了 dictionary 但从未退回 defaults...您需要：

[defaults setObject:dictionary forKey:@"uniqueSentToday"];

保存默认值。

Answer 2

您需要将字典存储回用户默认值，因为您收到的字典是不可变的。尽管您将其设置为可变的，但更改不会反映在用户默认的原始存储字典中。

NSUserDefaults 在使用应用程序时保存并重新加载，但在应用程序重新启动时重置

NSUserDefaults save and reload while using app but reset when app is restarted

objective-c

nsuserdefaults

ios