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Alamofire初探(后台下载)

2019-09-24 17:39:47 作者：互联网

Alamofire后台下载

后台下载

先来看看苹果原生后台下载
Alamofire后台下载

后台下载

从iOS7以来，苹果推出了NSURLSession后，可以实现后台下载任务

先来看看苹果原生后台下载

设置后台下载请求

let urlString:String = "http://dldir1.qq.com/qqfile/QQforMac/QQ_V6.5.5.dmg"
let config = URLSessionConfiguration.background(withIdentifier: createID())
let session = URLSession.init(configuration: config, delegate: self, delegateQueue: OperationQueue.main)
let downloadTask: URLSessionDownloadTask = session.downloadTask(with: URL(string: urlString)!)
downloadTask .resume()

AppDelegate代理方法(当应用处于后台，且后台下载任务完成时回调)

//用于保存后台下载的completionHandler
    var backgroundSessionCompletionHandler: (() -> Void)?
    func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: @escaping () -> Void) {
        
        print("handleEventsForBackgroundURLSession - \(identifier)")
        self.backgroundSessionCompletionHandler = completionHandler
    }

URLSessionDownloadDelegate代理方法

func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
        print("下载完成 - \(location)")
        let locationPath = location.path
        //拷贝到用户目录（文件名以时间戳命名）
        let documnets = NSHomeDirectory() + "/Documents/" + lgCurrentDataTurnString() + ".dmg"
        //创建文件管理器
        let fileManager = FileManager.default
        
        try! fileManager.moveItem(atPath: locationPath, toPath: documnets)
    }
    
    func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
        print(" bytesWritten \(bytesWritten)\n totalBytesWritten \(totalBytesWritten)\n totalBytesExpectedToWrite \(totalBytesExpectedToWrite)")
        print("下载进度: \(Double(totalBytesWritten)/Double(totalBytesExpectedToWrite))\n")
    }
    func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
        print("后台任务下载回来,当前线程-\(Thread.current)")

        DispatchQueue.main.async {
        
            guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
                return
            }
            guard let backHandler = appDelegate.backgroundSessionCompletionHandler else {
                return
            }
            backHandler()
        }
    }

注意: App Transport Security Settings -> Allow Arbitrary Loads -> YES
注意：urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL)方法中，location只是一个磁盘上该文件的临时 URL，只是一个临时文件，需要自己使用FileManager将文件写到应用的目录下（一般来说这种可以重复获得的内容应该放到cache目录下），因为当你从这个委托方法返回时，该文件将从临时存储中删除
注意：最好将handleEventsForBackgroundURLSession中completionHandler保存，在该方法中待下载数据和UI刷新做完后，再调用completionHandler()
Swift try?,try! as!,as? 的使用
- try? 告诉系统可能有错, 也可能没错, 如果发生错误, 那么返回nil, 如果没有发生错误, 会将数据包装成一个可选类型的值返回给我们
- try! 告诉系统一定没错, 如果发生错误, 程序会崩溃. 不推荐使用
- as! 向下转型(Downcasting)时使用,由于是强制类型转换，如果转换失败会报runtime运行错误
- as?和as!操作符的转换规则是一样的，只是as?在转换失败之后会返回nil对象，转换成功之后返回一个可选类型(optional)，需要我们拆包使用。由于as?转换失败也不会报错，所以对于能够100%确定使用as!能够转换成功的，使用as!,否则使用as?

Alamofire后台下载

创建一个单例，初始化请求，便于回调

struct LGBackgroundManger {
    static let shared = LGBackgroundManger()
    let manager: SessionManager = {
        let configuration = URLSessionConfiguration.background(withIdentifier: "com.lgcooci.AlamofireTest.demo")
        configuration.httpAdditionalHeaders = SessionManager.defaultHTTPHeaders
        return SessionManager(configuration: configuration)
    }()
}

Alamofire下载

LGBackgroundManger.shared.manager
            .download(urlString, method: .get, parameters: nil) {
                (url, response) -> (destinationURL: URL, options: DownloadRequest.DownloadOptions) in
                let documentUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first
                let fileUrl = documentUrl?.appendingPathComponent(response.suggestedFilename ?? "123.dmg")
                return (fileUrl!, [.createIntermediateDirectories,.removePreviousFile])
            }.response { (downloadResponse) in
                print("下载回调信息:\(downloadResponse)")
            }.downloadProgress { (progress) in
                print("下载进度：\(progress)")
        }

AppDelegate代理回调

func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: @escaping () -> Void) {
        
        print("handleEventsForBackgroundURLSession - \(identifier)")
        LGBackgroundManger.shared.manager.backgroundCompletionHandler = completionHandler
    }

注意: Manager needs to be retained during the session else we get HTTP Error Code -999 .
After defining manager as global it was retained. Could have defined it as Stored property as well for the class.

标签：completionHandler,print,session,let,初探,后台,Alamofire,下载
来源： https://blog.csdn.net/GuanZeJun123/article/details/101296696