NSCache是​​否在ViewControllers中持续存在？

Question

这是我第一次使用NSCache而且我知道它不适用于应用午餐。

但它是否会在ViewControllers中持续存在？...意思是......如果我在cache object上设置ViewController A，然后移至ViewController B，我仍然可以访问它？

我的问题与我在代码中遇到的问题有关。我在ViewController B，我设置了缓存对象。然后转到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???我的观点非常便宜，所以我认为没有理由放弃缓存对象

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]);
    }
}

Answer 1

NSCache是​​某种NSMutableDictionary。 不同之处在于，当NSCache检测到过大的内存压力时，它会释放一些键值对。 在ViewControllerA中，您可以创建NSCache对象

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

在ViewControllerB中，再次创建一个NSCache对象

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

因此它将是两个不同的对象，具有两组不同的键值对。 如果你需要某种存储，你可以编写一个包含一个NSCache对象的单例类。