ios – 如何设置NSURLRequest缓存过期？

想法是使用连接：willCacheResponse：方法.在缓存响应之前,它将被执行,在那里我们可以改变响应并返回新的,或返回nil,并且响应将不被缓存.当我使用AFNetworking,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;
  }];

其中responseWithExpirationDuration类别：

@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

所以,我们根据http/1.1在http header中设置以秒为单位的到期时间为此,我们需要设置一个标题：缓存控制：s-maxage或max-age然后创建新的缓存响应,因为属性是只读的,并返回新的对象.