Question

我对使用Cocoa进行IOS编程很新，我正在使用Swift。我使用带有自定义委托的NSURLSession数据会话从JSON API获取数据，而不是闭包。使用自定义委托的原因是我必须进行基本身份验证，并且还注入了一个自定义缓存控制标头来控制缓存行为（我的API根本不包括响应中任何与缓存相关的标头）。

所有这一切都很完美，但仅适用于仅调用一次URLSession：dataTask：didReceiveData：方法的请求。一旦我得到几次调用didReceivedData方法的更大响应（大约20-30kBytes），就不会调用URLSession：dataTask：willCacheResponse：completionHandler：方法，因此我的响应不会被缓存。在5分钟内重新发出相同的请求将再次向服务器发出请求，这对于响应仅一次调用didReceiveData的请求不会发生。 URLSession：task：didCompleteWithError：方法被正确调用并在所有情况下都继续。

URLSession的文档：dataTask：willCacheResponse：completionHandler：method（https://developer.apple.com/library/IOs/documentation/Foundation/Reference/NSURLSessionDataDelegate_protocol/index.html#//apple_ref/occ/intfm/NSURLSessionDataDelegate/URLSession:dataTask:willCacheResponse:completionHandler :)说只有在处理请求的NSURLProtocol决定这样做时才会调用此方法，但我真的不明白该怎么做做到这一点。

非常欢迎任何反馈和想法！

这是发出HTTP请求的代码：

    let config = NSURLSessionConfiguration.defaultSessionConfiguration()
    config.URLCache = NSURLCache.sharedURLCache()
    //config.URLCache = NSURLCache(memoryCapacity: 512000000, diskCapacity: 1000000000, diskPath: "urlCache")

    let urlString = apiUrlForFilter(filter, withMode: mode, withLimit: limit, withOffset: offset)
    let url = NSURL(string: urlString)

    var policy: NSURLRequestCachePolicy?
    if ignoreCache == true {
        policy = .ReloadIgnoringLocalCacheData
    } else {
        policy = .UseProtocolCachePolicy
    }

    let request = NSURLRequest(URL: url!, cachePolicy: policy!, timeoutInterval: 20)
    let session = NSURLSession(configuration: config, delegate: self, delegateQueue: nil)
    let task = session.dataTaskWithRequest(request)
    task.resume()

我实现了以下委托功能：

URLSession：didReceiveChallenge：completionHandler：处理SSL证书信任，
URLSession：task：didReceiveChallenge：completionHandler：处理基本身份验证
URLSession：dataTask：didReceiveResponse：completionHandler：读取一些特定的标题并将它们保存为实例变量

另外，重要的代码：

URLSession：dataTask：didReceiveData：在数据到达时为更大的HTTP请求响应而累积数据：

func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
    if receivedData == nil {
        receivedData = NSMutableData()
    }
    receivedData!.appendData(data)
    println("did receive data: \(receivedData!.length) bytes")
}

URLSession：dataTask：willCacheResponse：completionHandler：注入我自己的Cache-Control标头：

func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, willCacheResponse proposedResponse: NSCachedURLResponse, completionHandler: (NSCachedURLResponse!) -> Void) {
    println("willCacheResponse was called")

    let response: NSURLResponse = proposedResponse.response
    let httpResponse = response as NSHTTPURLResponse
    var headers = httpResponse.allHeaderFields

    var modifiedHeaders = headers        
    modifiedHeaders.updateValue("max-age=300", forKey: "Cache-Control")
    let modifiedResponse = NSHTTPURLResponse(URL: httpResponse.URL!, statusCode: httpResponse.statusCode, HTTPVersion: "HTTP/1.1", headerFields: modifiedHeaders)
    let cachedResponse = NSCachedURLResponse(response: modifiedResponse!, data: proposedResponse.data, userInfo: proposedResponse.userInfo, storagePolicy: proposedResponse.storagePolicy)
    completionHandler(cachedResponse)
}

URLSession：task：didCompleteWithError：检查错误的完整响应并调用此类通过初始化获得的回调闭包，以进一步继续执行结果数据：

func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
    session.finishTasksAndInvalidate()

    if error != nil {
        var string: String?
        if errorString != nil {
            string = errorString
        } else {
            string = Helpers.NSURLErrorDomainErrorForCode(error!.code)
        }
        errorCallback(string!)
        return
    }

    if receivedData == nil {
        errorCallback("the query returned an empty result")
        return
    }

    var jsonError: NSError?
    let results: AnyObject! = NSJSONSerialization.JSONObjectWithData(receivedData!, options: NSJSONReadingOptions.AllowFragments, error: nil)

    if results == nil {
        errorCallback("the data returned was not valid JSON")
        return
    }

    let jsonParsed = JSONValue.fromObject(results)

    if let parsedAPIError = jsonParsed!["error"]?.string {
        errorCallback("API error: \(parsedAPIError)")
        return
    }

    callback(jsonParsed!, self.serverTime!)
}

当大于几千字节时，NSURLSession URL响应不会被缓存

0 个答案: