NSURLCache未缓存

Question

所以我创建了NSURLCache的子类，每次我调用loadHTMLFromString:时，它都会先调用storeCachedRequest:forRequest:，然后再调用cachedResponseForRequest:。这就是我所拥有的：

- (NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request
{
    NSString *pathString = [[request URL] absoluteString];

    NSCachedURLResponse * response = [super cachedResponseForRequest:request];
    if (response != nil)
        return response;
    else {
        NSString* myString= @"testing";

        NSData* data=[myString dataUsingEncoding: NSASCIIStringEncoding ];

        //
        // Create the cacheable response
        //
        NSURLResponse *response =
        [[[NSURLResponse alloc]
          initWithURL:[request URL]
          MIMEType:[self mimeTypeForPath:pathString]
          expectedContentLength:[data length]
          textEncodingName:nil]
         autorelease];
        NSCachedURLResponse * cachedResponse =
        [[[NSCachedURLResponse alloc] initWithResponse:response data:data] autorelease];

        [self storeCachedResponse:cachedResponse forRequest:request] ;

        //NSLog(@"DEFAULT CACHE WITH URL %@", [[request URL] absoluteString]);
        return [super cachedResponseForRequest:request];
    }

    return nil;
}

- (void)storeCachedResponse:(NSCachedURLResponse *)cachedResponse forRequest:(NSURLRequest *)request
{
    [super storeCachedResponse:cachedResponse forRequest:request];

    NSLog(@"STORE CACHED RESPONSE WITH URL %@", [[request URL] absoluteString]);
}

问题是，当我在保存后立即调用cachedResponseForRequest:时，响应总是为空。为什么会这样呢？

我有：

NSURLRequest * req = [NSURLRequest requestWithURL:[NSURL URLWithString:self.imageSource_]];
NSCachedURLResponse * response = [[NSURLCache sharedURLCache] cachedResponseForRequest:req];

if (response == nil)
    NSLog(@"RESPONSE IS NIL");
else {
    NSString* theString = [[NSString alloc] initWithData:response.data encoding:NSASCIIStringEncoding];
    NSLog(@"RESPONSE IS NOT NIL %@", theString);
}

并且它总是打印出响应为空。url字符串与storeCachedResponse时相同。由于某些原因，它不是缓存。我已经将缓存大小设置为一定的大小。

Answer 1

不是100%确定，但我认为你需要使用你的NSURLConnection返回的NSURLResponse，而不是创建你自己的。我怀疑如果只是创建一个NSURLResponse，它没有为缓存设置任何标头，因此NSURLCache假设它应该缓存这个特定的结果。

Answer 2

在选择要缓存或不缓存的内容时，默认NSURLCache似乎是相当随机的。你最好的办法可能是将其子类化，并直接在cachedResponseForRequest中处理你所关心的文件的缓存，剩下的留给超级用户来处理。