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这是我第一次使用NSCache，我知道它不会在应用程序午餐中持续存在。

但是它会持续存在ViewControllers吗？...意思是...如果我将其设置为cache object打开ViewController A然后移动到ViewController B我仍然可以访问它吗？

我的问题与我在代码中遇到的问题有关。我在ViewController B并且我设置了缓存对象。然后移动到ViewController B并尝试检索该对象，但从未找到。

这是正常的还是我的代码有问题？？？我的视图非常便宜，所以我看不出它为什么会丢弃缓存对象

ViewController A（使用缓存）

- (void) searchDone:(NSDictionary*)response {

    NSString * str = input.text;
    str = [str stringByReplacingOccurrencesOfString:@" " withString:@""];
    NSString* cachedKey = [str stringByReplacingOccurrencesOfString:@"#" withString:@""];
    cachedKey = [cachedKey lowercaseString];

    //
    // Cache
    //
    NSCache * cache = [[NSCache alloc]init];
    NSDictionary* chachedData = [cache objectForKey:cachedKey];

    // Check for a cached version of this
    if ( chachedData ) {

        NSLog(@"There is a cache");

        NSTimeInterval timeDifferenceBetweenDates = [chachedData[@"time"] timeIntervalSinceNow];
        CGFloat time = fabsf(timeDifferenceBetweenDates);

        if ( time < sysTraditionalSearchCacheTime ) {
            NSLog(@"using cache");
            NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:input.text,@"input",chachedData,@"response",nil];

            [[NSNotificationCenter defaultCenter]
             postNotificationName:@"closeSearch"
             object:nil
             userInfo:dictionary];
            return;
        }
        [cache removeObjectForKey:cachedKey];
    }

ViewController B（缓存设置器）

- (void) notificationCloseSearch:(NSNotification*) notification {

    input.text = [[notification userInfo] valueForKey:@"input"];

    NSDictionary* response = [[notification userInfo] valueForKey:@"response"];
    NSString * str = input.text;
    str = [str stringByReplacingOccurrencesOfString:@" " withString:@""];
    NSString* cachedKey = [str stringByReplacingOccurrencesOfString:@"#" withString:@""];
    cachedKey = [cachedKey lowercaseString];
    //
    // Cache
    //
    NSCache * cache = [[NSCache alloc]init];
    NSDictionary* chachedData = [cache objectForKey:cachedKey];

    // Check for a cached version of this
    if ( chachedData ) {
        NSTimeInterval timeDifferenceBetweenDates = [chachedData[@"time"] timeIntervalSinceNow];
        CGFloat time = fabsf(timeDifferenceBetweenDates);
        if ( time >= sysTraditionalSearchCacheTime ) {
            [cache removeObjectForKey:cachedKey];
        }
    } else { // if there is no cache then set one
        NSLog(@"setting cache key %@",cachedKey);
        NSDate* now = [NSDate date];
        NSMutableDictionary* newResopnse = [[NSMutableDictionary alloc]initWithDictionary:response];
        [newResopnse setObject:now forKey:@"time"];
        response = [[NSDictionary alloc] initWithDictionary:newResopnse];
        [cache setObject:response forKey:cachedKey];
        NSLog(@"cached %@",[cache objectForKey:cachedKey]);
    }
}
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1 回答 1

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NSCache 是某种 NSMutableDictionary。不同的是，当 NSCache 检测到内存压力过大时，它会释放一些键值对。在 ViewControllerA 你创建 NSCache 对象

NSCache * cache = [[NSCache alloc]init];

在 ViewControllerB 中你又创建了一个 NSCache 对象

NSCache * cache = [[NSCache alloc]init];

所以这将是两个不同的对象，具有两组不同的键值对。如果您需要某种存储，您可以编写包含一个 NSCache 对象的单例类。

于 2013-09-09T11:19:52.750 回答