后台使用单个 NSURLSession uploadTaskWithRequest 上传多张图片

Question

我想使用一个uploadTaskWithRequest 方法在后台上传多张图片。在尝试以下代码时，后台会话不支持来自 NSData 的上传任务...请教如何实现这一点

func createRequest (param : NSDictionary ,imagearray :NSMutableArray, strURL : String) -> NSURLRequest {

    let boundary = generateBoundaryString()

    let url = NSURL(string: strURL)
    let request = NSMutableURLRequest(URL: url!)

    request.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
    request.HTTPMethod = "POST"
    request.HTTPBody = createBodyWithParameters(param, image_array:imagearray,boundary: boundary);

    return request
}

   func createBodyWithParameters(parameters: NSDictionary,image_array:NSMutableArray,boundary: String) -> NSData {
 let body = NSMutableData()         
for (key, value) in parameters {
      if(value is String || value is NSString){
            body.appendString("--\(boundary)\r\n")
            body.appendString("Content-Disposition: form-data; name=\"\(key)\"\r\n\r\n")
            body.appendString("\(value)\r\n")
        }
    }
    var i = 0;
    for image in image_array {
        let filename = "image\(i).jpg"
        let data = UIImagePNGRepresentation(image as! UIImage);
        let mimetype = "image/png"
        body.appendString("--\(boundary)\r\n")
        body.appendString("Content-Disposition: form-data; name=\"\(self.filePathKey)\"; filename=\"\(filename)\"\r\n")
        body.appendString("Content-Type: \(mimetype)\r\n\r\n")
        body.appendData(data!)
        body.appendString("\r\n")
        i += 1;
    }

    body.appendString("--\(boundary)--\r\n")
    //        NSLog("data %@",NSString(data: body, encoding: NSUTF8StringEncoding)!);
    return body
}

func postrequestwithformdata(requesturl:String,postparams:NSDictionary,postformadata:NSMutableArray,requestId:Int)  
{

    self.requestid = requestId;
    let requestformdata = self.createRequest(postparams, imagearray: postformadata, strURL: requesturl);
    let configuration = NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier(Contants.identifier)
    let session: NSURLSession = NSURLSession(configuration:configuration, delegate: self, delegateQueue: NSOperationQueue.mainQueue());
    let task: NSURLSessionUploadTask = session.uploadTaskWithRequest(requestformdata, fromData: requestformdata.HTTPBody!);
    task.resume();

}

Answer 1

要在后台会话中上传，必须先将数据保存到文件中。

1. 使用writeToFile:options:将数据保存到文件中。
2. 调用 NSURLSession uploadTaskWithRequest:fromFile: 来创建任务。注意请求中不能包含HTTPBody中的数据，否则上传会失败。
3. 在 URLSession:didCompleteWithError: 委托方法中处理完成。

您可能还想处理应用在后台时完成的上传。

1. 在 AppDelegate 中实现 application:handleEventsForBackgroundURLSession:completionHandler。
2. 使用提供的标识符创建一个 NSURLSession。
3. 按照通常的上传响应委托方法（例如处理URLSession:didCompleteWithError:中的响应）
4. 在您完成事件处理后致电URLSessionDidFinishEventsForBackgroundURLSession。

为了便于管理，请为每个上传任务创建一个NSURLSession，每个任务都有一个唯一标识符。

请参阅URL Session Programming Guide了解实施详情。

AppDelegate 示例：

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate, NSURLSessionDelegate, NSURLSessionTaskDelegate {

    var window: UIWindow?

    typealias CompletionHandler = () -> Void

    var completionHandlers = [String: CompletionHandler]()

    var sessions = [String: NSURLSession]()


    func upload(request: NSURLRequest, data: NSData)
    {
        // Create a unique identifier for the session.
        let sessionIdentifier = NSUUID().UUIDString

        let directoryURL = NSFileManager.defaultManager().URLsForDirectory(.CachesDirectory, inDomains: .UserDomainMask).first!
        let fileURL = directoryURL.URLByAppendingPathComponent(sessionIdentifier)

        // Write data to cache file.
        data.writeToURL(fileURL, atomically: true);

        let configuration = NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier(sessionIdentifier)

        let session: NSURLSession = NSURLSession(
            configuration:configuration,
            delegate: self,
            delegateQueue: NSOperationQueue.mainQueue()
        )

        // Store the session, so that we don't recreate it if app resumes from suspend.
        sessions[sessionIdentifier] = session

        let task = session.uploadTaskWithRequest(request, fromFile: fileURL)

        task.resume()
    }

    // Called when the app becomes active, if an upload completed while the app was in the background.
    func application(application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: CompletionHandler) {

        let configuration = NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier(identifier)

        if sessions[identifier] == nil {

            let session = NSURLSession(
                configuration: configuration,
                delegate: self,
                delegateQueue: NSOperationQueue.mainQueue()
            )

            sessions[identifier] = session
        }

        completionHandlers[identifier] = completionHandler
    }

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

        // Handle background session completion handlers.
        if let identifier = session.configuration.identifier {

            if let completionHandler = completionHandlers[identifier] {
                completionHandler()
                completionHandlers.removeValueForKey(identifier)
            }

            // Remove session
            sessions.removeValueForKey(identifier)
        }

        // Upload completed.
    }
}

要在单个请求中上传多个图像，必须首先将图像编码为 multipart/formdata MIME 类型，就像您所做的那样。不同之处在于整个 MIME 消息必须保存到单个文件中，该文件是上传到服务器的文件。

这里是一个例子，展示了如何做到这一点。它通过将 MIME 部分直接序列化为文件来工作。您也可以在 NSData 中构建消息，尽管在处理大文件时可能会遇到内存限制。

func uploadImages(request: NSURLRequest, images: [UIImage]) {

    let uuid = NSUUID().UUIDString
    let boundary = String(count: 24, repeatedValue: "-" as Character) + uuid

    // Open the file
    let directoryURL = NSFileManager.defaultManager().URLsForDirectory(.CachesDirectory, inDomains: .UserDomainMask).first!

    let fileURL = directoryURL.URLByAppendingPathComponent(uuid)
    let filePath = fileURL.path!

    NSFileManager.defaultManager().createFileAtPath(filePath, contents: nil, attributes: nil)

    let file = NSFileHandle(forWritingAtPath: filePath)!


    // Write each image to a MIME part.
    let newline = "\r\n"

    for (i, image) in images.enumerate() {

        let partName = "image-\(i)"
        let partFilename = "\(partName).png"
        let partMimeType = "image/png"
        let partData = UIImagePNGRepresentation(image)

        // Write boundary header
        var header = ""
        header += "--\(boundary)" + newline
        header += "Content-Disposition: form-data; name=\"\(partName)\"; filename=\"\(partFilename)\"" + newline
        header += "Content-Type: \(partMimeType)" + newline
        header += newline

        let headerData = header.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)

        print("")
        print("Writing header #\(i)")
        print(header)

        print("Writing data")
        print("\(partData!.length) Bytes")

        // Write data
        file.writeData(headerData!)
        file.writeData(partData!)
    }

    // Write boundary footer
    var footer = ""
    footer += newline
    footer += "--\(boundary)--" + newline
    footer += newline

    print("")
    print("Writing footer")
    print(footer)

    let footerData = footer.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
    file.writeData(footerData!)

    file.closeFile()

    // Add the content type for the request to multipart.
    let outputRequest = request.copy() as! NSMutableURLRequest

    let contentType = "multipart/form-data; boundary=\(boundary)"
    outputRequest.setValue(contentType, forHTTPHeaderField: "Content-Type")


    // Start uploading files.
    upload(outputRequest, fileURL: fileURL)
}