Alamofire network

Alamofire鏈接

Alamofire是一個純粹的網絡庫，關於UI的部分有另外的封裝，比如AlamofireImage
和AlamofireNetworkActivityIndicator

一、URLSession

步驟

1. 創建session會話
2. 根據url創建dataTask
3. 取消掛起狀態，resume()

        URLSession.shared.dataTask(with: url) { (data, response, error) in
            if error == nil {
                print("請求成功 \(String(describing: response))")
            }
        }.resume()

URLSession的三種configuration

        let configuration1 = URLSessionConfiguration.default
        print("configuration1沙盒大小:\(String(describing: configuration1.urlCache?.diskCapacity))")
        print("configuration1內存大小:\(String(describing: configuration1.urlCache?.memoryCapacity))")
        
        let configuration2 = URLSessionConfiguration.ephemeral
        print("configuration2沙盒大小:\(String(describing: configuration2.urlCache?.diskCapacity))")
        print("configuration2內存大小:\(String(describing: configuration2.urlCache?.memoryCapacity))")

/*
打印結果：
configuration1沙盒大小:Optional(10000000)
configuration1內存大小:Optional(512000)
configuration2沙盒大小:Optional(0)
configuration2內存大小:Optional(512000)
*/

.default，默認模式，系統會創建一個持久化的緩存並在用戶鑰匙串中存儲證書
.ephemeral，系統沒有持久化存儲，所有內容的生命週期都與session相同，當session無效時所有內容自動釋放
.background(withIdentifier identifier: String)，創建一個可以在後臺甚至APP已經關閉的時候仍然在傳輸數據的會話，默認是掛起狀態

• 實現後臺下載與進度打印

1. 創建session會話
2. 根據url創建dataTask
3. 取消掛起狀態，resume()

        let configuration3 = URLSessionConfiguration.background(withIdentifier: self.createID())
        
        let session = URLSession.init(configuration: configuration3, delegate: self, delegateQueue: OperationQueue.main)
        
        session.downloadTask(with: url).resume()

4. 代理回調delegate

//ViewController
extension ViewController:URLSessionDownloadDelegate {
    func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
        print("下載完成-\(location)")
        let locationPath = location.path
        //取得新地址，文件以當前時間的時間戳命名
        let documents = NSHomeDirectory() + "/Documents" + self.stringFromNow() + ".mp4"
        print("新地址:\(documents)")
        //移動文件
        let fileManager = FileManager.default
        try! fileManager.moveItem(atPath: locationPath, toPath: documents)
    }
    
    func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
        print("下載進度:\(totalBytesWritten/totalBytesExpectedToWrite)")
    }
}

5. 申請後臺下載權限，AppDelegate設置回調CompletionHandler

//AppDelegate設置回調
    var backgroundSessionCompletionHandler: (() -> Void)?

    func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: @escaping () -> Void) {
        self.backgroundSessionCompletionHandler = completionHandler
    }

6. AppDelegate的回調completionHandler執行
   從handleEventsForBackgroundURLSession方法的官方解釋（option+方法查看官方解釋）中知道

completionHandler
The completion handler to call when you finish processing the events. Calling this completion handler lets the system know that your app’s user interface is updated and a new snapshot can be taken.

因此，在AppDelegate設置的回調completionHandler需要在下載完成後在URLSessionDownloadDelegate執行，告訴系統執行完畢可以回收並刷新UI，避免影響系統運行性能

func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
        print("後臺任務下載完成後回來")
        DispatchQueue.main.async {
            guard let appDelegate = UIApplication.shared.delegate as? AppDelegate, let backgroundHandler = appDelegate.backgroundSessionCompletionHandler else { return }
            backgroundHandler()
        }
    }

二、Http:三次握手四次揮手