iphone:磁盘上的NSURLCache

Question

我在将URLResponses缓存到磁盘时遇到问题.我想这样,因为我下载的数据需要重新加载,当它的http-header中的expires-tag满足时,而不是更早.此外,我希望iPod touch-Users能够在线下载一次数据,然后离线使用.

我这样做是为了缓存内存中的东西,但在重新启动应用程序时失败:

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在评论中正确陈述:

我发现如果(a)你使用NSURLRequestUseProtocolCachePolicy的默认NSURLRequest cachePolicy; (b)响应不包括Cache-Control标头,它不会缓存到磁盘.如果您使用NSURLRequestReturnCacheDataElseLoad的cachePolicy,或者如果来自服务器的响应指定了特定的Cache-Control标头(例如public,max-age = 1835400),它将缓存到持久存储.