我正在使用 AFNetworking，需要在一个响应中缓存数据几分钟。所以我在应用委托中设置了 NSUrlCache，然后在我的请求中设置它：
NSMutableURLRequest *request = //obtain request;
request.cachePolicy = NSURLRequestReturnCacheDataElseLoad;
然后如何设置过期日期：如果数据是在 n 分钟前加载的，则询问服务器而不是磁盘的响应？
编辑：
假设服务器不支持缓存，我需要在代码中管理它。
【问题讨论】：
标签： ios objective-c caching
所以，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，在那里我们可以更改响应并返回新的，或者返回 nil 并且不会缓存响应。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头中设置过期秒数 为此，我们需要设置一个标题： 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。
【讨论】：
UIImageView (_AFNetworking) 到setImageWithURLRequest，我如何调用setCacheResponseBlock，因为它不公开af_imageRequestOperation，并且没有设置缓存块的功能？
使用 URLSession 的 @HotJard 解决方案的 Swift 等效项
extension CachedURLResponse {
func response(withExpirationDuration duration: Int) -> CachedURLResponse {
var cachedResponse = self
if let httpResponse = cachedResponse.response as? HTTPURLResponse, var headers = httpResponse.allHeaderFields as? [String : String], let url = httpResponse.url{
headers["Cache-Control"] = "max-age=\(duration)"
headers.removeValue(forKey: "Expires")
headers.removeValue(forKey: "s-maxage")
if let newResponse = HTTPURLResponse(url: url, statusCode: httpResponse.statusCode, httpVersion: "HTTP/1.1", headerFields: headers) {
cachedResponse = CachedURLResponse(response: newResponse, data: cachedResponse.data, userInfo: headers, storagePolicy: cachedResponse.storagePolicy)
}
}
return cachedResponse
}
}
然后在你的自定义类中实现 URLSessionDataDelegate 协议
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, willCacheResponse proposedResponse: CachedURLResponse, completionHandler: @escaping (CachedURLResponse?) -> Void) {
if dataTask.currentRequest?.cachePolicy == .useProtocolCachePolicy {
let newResponse = proposedResponse.response(withExpirationDuration: 60)
completionHandler(newResponse)
}else {
completionHandler(proposedResponse)
}
}
不要忘记创建配置和会话，将自定义类作为委托引用传递，例如
let session = URLSession(
configuration: URLSession.shared.configuration,
delegate: *delegateReference*,
delegateQueue: URLSession.shared.delegateQueue
)
let task = session.dataTask(with: request)
task.resume()
【讨论】：
NSURLCache 中的响应过期由 HTTP 响应中的 Cache-Control 标头控制。
编辑我看到你更新了你的问题。如果服务器未在响应中提供 Cache-Control 标头，则不会对其进行缓存。对该端点的每个请求都将加载该端点，而不是返回缓存的响应。
【讨论】：