如何设置NSURLRequest缓存过期? [英] How to set NSURLRequest cache expiration?

问题描述

我正在使用AFNetworking，并且需要在一个响应中将数据缓存几分钟.因此，我在应用程序委托中设置了NSUrlCache，然后在我的请求中对其进行了设置:

I'm using AFNetworking and need to cache data in one response for a several minutes. So I set NSUrlCache in app delegate and then in my request setting up it:

NSMutableURLRequest *request = //obtain request; 
request.cachePolicy = NSURLRequestReturnCacheDataElseLoad;

然后如何设置到期日期:如果数据加载时间超过n分钟，请询问服务器而不是磁盘的响应?

How then set expiration date: if the data was loaded more than n minutes ago, ask response from server and not from disk?

假设服务器不支持缓存，我需要用代码进行管理.

Assume that server doesn't support caching, I need to manage it in code.

推荐答案

因此，我找到了解决方案.

So, I found the solution.

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:

The idea is to use connection:willCacheResponse: method. Before cache the response it will be executed and there we can change response and return new, or return nil and the response will not be cached. As I use AFNetworking, there is a nice method in operation:

- (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来自类别:

@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

因此，我们根据 http/1.1 在http标头中设置以秒为单位的到期时间 为此，我们需要设置以下标头之一: 过期，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，并返回新对象.

So, we set expiration in seconds in http header according to http/1.1 For that we need one of headers to be set up: Expires, Cache-Control: s-maxage or max-age Then create new cache response, because the properties is read only, and return new object.

这篇关于如何设置NSURLRequest缓存过期?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！