iPhone:磁盘上的 NSURLCache

Question

我在将 URLResponse 缓存到磁盘时遇到问题。我想要这样，因为我正在下载的数据需要在满足 http header 中的过期标签时重新加载，而不是更早。另外，我希望 iPod touch 用户能够在线下载一次数据，然后离线使用。

我正在这样做，它可以很好地在内存中缓存内容，但在重新启动应用程序时会失败:

NSURLRequest* menuRequest = [NSURLRequest requestWithURL:mensaURL cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval: 10];
NSCachedURLResponse* cachedMenuResponse = [[NSURLCache sharedURLCache] cachedResponseForRequest:menuRequest];
if (cachedMenuResponse) {
    // received data is a member of that class to which the asynchronous 
    // download writes and which is then being used in updateDataFromDownload
    // to retrieve my data structure from the download.
    self.receivedData = [NSMutableData dataWithData:[cachedMenuResponse data]];
    [self updateDataFromDownload];
    NSLog(@"using data from cache");
} else {
    NSLog(@"opening connection");
    [NSURLConnection connectionWithRequest:menuRequest delegate:self];
}

Answer 1

AFAIK NSURLRequest/NSURLConnection 支持从 iOS 5 缓存到磁盘。

更新:@Rob 在评论中正确指出:

I've found that if (a) you use the default NSURLRequest cachePolicy of NSURLRequestUseProtocolCachePolicy; and (b) the response doesn't include the Cache-Control header, it won't cache to disk. If you use a cachePolicy of NSURLRequestReturnCacheDataElseLoad, or if the response from the server specifies a particular Cache-Control header (e.g. public, max-age=1835400), it will cache to persistent storage.