如何设置NSURLRequest缓存过期？

因此，我找到了解决方案。

这个想法是使用connection:willCacheResponse:方法。在缓存响应之前，它将被执行，我们可以在其中更改响应并返回new，或者返回nil，并且响应不会被缓存。当我使用AFNetworking时，有一个很好的操作方法：

- (void)setCacheResponseBlock:(NSCachedURLResponse * (^)(NSURLConnection *connection, NSCachedURLResponse *cachedResponse))block;

添加代码：

  [operation setCacheResponseBlock:^NSCachedURLResponse *(NSURLConnection *connection, NSCachedURLResponse *cachedResponse) {
    if([connection currentRequest].cachePolicy == NSURLRequestUseProtocolCachePolicy) {
      cachedResponse = [cachedResponse responseWithExpirationDuration:60];
    }
    return cachedResponse;
  }];

responseWithExpirationDuration来自哪里：

@interface NSCachedURLResponse (Expiration)
-(NSCachedURLResponse*)responseWithExpirationDuration:(int)duration;
@end

@implementation NSCachedURLResponse (Expiration)

-(NSCachedURLResponse*)responseWithExpirationDuration:(int)duration {
  NSCachedURLResponse* cachedResponse = self;
  NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse*)[cachedResponse response];
  NSDictionary *headers = [httpResponse allHeaderFields];
  NSMutableDictionary* newHeaders = [headers mutableCopy];

  newHeaders[@"Cache-Control"] = [NSString stringWithFormat:@"max-age=%i", duration];
  [newHeaders removeObjectForKey:@"Expires"];
  [newHeaders removeObjectForKey:@"s-maxage"];

  NSHTTPURLResponse* newResponse = [[NSHTTPURLResponse alloc] initWithURL:httpResponse.URL
                                                               statusCode:httpResponse.statusCode
                                                              HTTPVersion:@"HTTP/1.1"
                                                             headerFields:newHeaders];

  cachedResponse = [[NSCachedURLResponse alloc] initWithResponse:newResponse
                                                            data:[cachedResponse.data mutableCopy]
                                                        userInfo:newHeaders
                                                   storagePolicy:cachedResponse.storagePolicy];
  return cachedResponse;
}

@end

因此，我们根据http / 1.1在http标头中设置了以秒为单位的到期时间，为此，我们需要设置标头之一：Expires，Cache-Control：s-maxage或max-age然后创建新的缓存响应，因为属性为只读，并返回新对象。