removeAllCachedResponses无法清除sharedURLCache？

Question

我按了一个按钮来清除我的缓存：

    [[NSURLCache sharedURLCache]removeAllCachedResponses];

完成后，我检查sharedURLCache的大小：

NSInteger sizeInteger = [[NSURLCache sharedURLCache] currentDiskUsage];
float sizeInMB = sizeInteger / (1024.0f * 1024.0f);

sizeInMB是0.17，有时是0.13。从不0.0。为什么removeAllCachedResponses不会使sharedURLCache成为ZERO？

ps：在AppDelegate.m中didFinishLaunchingWithOptions：

NSURLCache *sharedCache = [[NSURLCache alloc] initWithMemoryCapacity:2 * 1024 * 1024
                                                                    diskCapacity:20 * 1024 * 1024
                                                                        diskPath:nil];

    [NSURLCache setSharedURLCache:sharedCache];

Answer 1

我用NSURLCache做过小实验。代码和日志如下：

NSUInteger memorySize = 1024 * 1024 * 64;
NSURLCache *sharedCache = [[NSURLCache alloc] initWithMemoryCapacity:memorySize diskCapacity:memorySize diskPath:nil];
[NSURLCache setSharedURLCache:sharedCache];
NSLog(@"cap: %ld", [[NSURLCache sharedURLCache] diskCapacity]);

NSInteger sizeInteger = [[NSURLCache sharedURLCache] currentDiskUsage];
float sizeInMB = sizeInteger / (1024.0f * 1024.0f);
NSLog(@"size: %ld,  %f", (long)sizeInteger, sizeInMB);

[[NSURLCache sharedURLCache] removeAllCachedResponses];

sizeInteger = [[NSURLCache sharedURLCache] currentDiskUsage];
sizeInMB = sizeInteger / (1024.0f * 1024.0f);
NSLog(@"size: %ld,  %f", (long)sizeInteger, sizeInMB);

[[NSURLCache sharedURLCache] removeAllCachedResponses];

sizeInteger = [[NSURLCache sharedURLCache] currentDiskUsage];
sizeInMB = sizeInteger / (1024.0f * 1024.0f);
NSLog(@"size: %ld,  %f", (long)sizeInteger, sizeInMB);

日志：

2015-08-05 11:26:29.901 lagoon[26845:533709] cap: 67108864
2015-08-05 11:26:29.904 lagoon[26845:533709] size: 86016,  0.082031
2015-08-05 11:26:29.907 lagoon[26845:533709] size: 123128,  0.117424
2015-08-05 11:26:29.910 lagoon[26845:533709] size: 123128,  0.117424

它是全新安装的应用程序，没有任何网络请求，并且已经占用了一些空间，您可以在日志中看到。所以我认为它在缓存中有一些额外的开销，而且它与真实的网络数据无关。

Answer 2

部分缓存是一个sqlite数据库。清除缓存可以清除数据库中的记录，但不能调低数据库的大小。这就是磁盘空间似乎不受影响的原因。

Answer 3

在笔测试（安全测试）期间，我在cache.db中遇到了iOS缓存url请求/响应的问题。

我试过用

URLCache.shared.removeCachedResponse（for：URLRequest）和URLCache.shared.removeAllCachedResponses（）

从API调用获得响应后，上述两个API似乎都没有工作

然后通过在AppDelegate中的didFinishLaunchingWithOptions中放入以下两行代码来实现它

// first remove all url cache from previous versions of app
URLCache.shared.removeAllCachedResponses()


// As we do not want to cache any request response so
// updated shared instance of url cache with custom url cache where
// memoryCapacity = 0, diskCapacity = 0 and diskPath = nil
URLCache.shared = URLCache(memoryCapacity: 0, diskCapacity: 0, diskPath: nil)