swift5 - 如何使用 BGTaskScheduler 在后台快速调用 API？

Question

在我的应用程序中，我们必须调用一项服务来刷新令牌。因此，出于这种想法，可以使用后台调度程序和调度任务来调用 API。

在那个计划任务中，我必须在后台进行静默呼叫，以提供新的令牌。因此，当用户打开应用程序时，不会遇到任何不便。

为此，我结合了后台调度程序（BGTaskScheduler），使用BGProcessingTask，进行API调用（使用URLSessionConfiguration.background(withIdentifier:)）

1. 点击项目名称—> 选择目标-> 转到签名和功能 —> 点击添加—> 背景模式

2. 检查后台获取和后台处理

3. 在 info.plist 中添加标识符

4. 创建自定义类，命名为BGTaskHelper：

   import UIKit
   import Foundation
   import BackgroundTasks
   
   
   let TASK_ID_REFRESH_TOKEN = "com.sample.refresh"
   let SESSION_ID_REFRESH_CALL = "com.sample.refreshCall"
   
   class BGTaskHelper: NSObject, URLSessionDelegate {    
       static let shared = BGTaskHelper()
   
   private lazy var urlSession: URLSession = {
       let config = URLSessionConfiguration.background(withIdentifier: SESSION_ID_REFRESH_CALL)
       config.isDiscretionary = true
       config.sessionSendsLaunchEvents = true
       return URLSession(configuration: config, delegate: self, delegateQueue: nil)
   }()
   
   func requestWith(strURL: String, method: String, params: [String: Any]?, completion: @escaping((Data?, URLResponse?, Error?)) -> Void) {
   
       guard let url = URL(string: strURL) else { return }
       print("REQUEST URL : =============== ", strURL)
   
       var request = URLRequest(url: url)
       request.httpMethod = method
       request.addValue("application/json", forHTTPHeaderField: "content-type")
   
       if let postParams = params {
           print("REQUEST PARAMS : =============== ", postParams)
           guard let httpbody = try? JSONSerialization.data(withJSONObject: postParams, options: []) else { return }
           request.httpBody = httpbody
       }
   
       let task = urlSession.dataTask(with: request) { (data, response, error) in
   
           guard let response = response, let data = data else {
               completion((nil, nil, error))
               return
           }
   
           // ------- Added to just print response --------------------------------
           do {
               let json = try JSONSerialization.jsonObject(with: data, options: []) as? [String:Any]
               print("RESPONSE JSON : =============== ", json ?? "")
           } catch let error{
               print("RESPONSE PARSING ERROR : =============== ", error)
           }
           // -----------------------------------------------------------------------
   
           completion((data, response, error))
       }
       task.resume()
   }
   
   static func registerAutoRefreshToken() {
   
       if #available(iOS 13.0, *) {
           BGTaskScheduler.shared.register(forTaskWithIdentifier: TASK_ID_REFRESH_TOKEN, using: nil) { task in
               task.setTaskCompleted(success: true)
               BGTaskHelper.shared.handleTokenRefresh(task: task)  //as! BGAppRefreshTask
           }
       } else {
           // Fallback on earlier versions
       }
   }
   
   static func scheduleTokenRefresh() {
   
       guard UserDefaults.standard.bool(forKey: "IS_LOGIN") == true else { return }
   
       if #available(iOS 13.0, *) {
   
           BGTaskScheduler.shared.cancelAllTaskRequests()
   
           let request = BGProcessingTaskRequest(identifier: TASK_ID_REFRESH_TOKEN)
           // Fetch no earlier than 15 minutes from now
           request.earliestBeginDate = Date(timeIntervalSinceNow: 15 * 60)
           request.requiresNetworkConnectivity = true
   
           do {
               try BGTaskScheduler.shared.submit(request)
           } catch {
               print("Could not schedule token refresh : ", error)
           }
       }
   }
   
   @available(iOS 13.0, *)
   func handleTokenRefresh(task: BGTask) { //BGAppRefreshTask
   
       // 1. Schedule a new refresh task
       BGTaskHelper.scheduleTokenRefresh()
   
       let queue = OperationQueue()
       queue.maxConcurrentOperationCount = 1
   
       // 2. Create an operation that performs the main part of the background task
   
       let operation = BlockOperation()
       operation.addExecutionBlock {
           if UserDefaults.standard.bool(forKey: "IS_LOGIN") == true {
               let dict: [String: Any] = ["userID" : "xyzUser",
                                          "token" : "last_saved_token"]
               BGTaskHelper.shared.requestWith(strURL: "https://example.com/xyzUser/tokenrefresh", method: "POST", params: dict) { (data, response, error) in
                   task.setTaskCompleted(success: true)
                   // saving new token
               }
           }
       }
   
   
       // 3. Provide an expiration handler for the background task that cancels the operation
       task.expirationHandler = {
           operation.cancel()
       }
   
       // 4. Inform the system that the background task is complete when the operation completes
       operation.completionBlock = {
           task.setTaskCompleted(success: !operation.isCancelled)
       }
   
       // 5. Start the operation
       queue.addOperation(operation)
   }
   }
   

5. 在AppDelegate, didFinishLaunchingWithOptions, 调用 :BGTaskHelper.registerAutoRefreshToken()

6. 在SceneDelegate, sceneDidEnterBackground, 调用 :BGTaskHelper.scheduleTokenRefresh()

这就是我所做的。我仍然没有完全测试它。但我很困惑这是否会完美运行？

• 这种组合是否正确？: BGTaskScheduler, BGProcessingTask,URLSessionConfiguration.background(withIdentifier:)
• 或者我应该BGAppRefreshTaskRequest改用BGProcessingTaskRequest吗？
• 对于请求呼叫，我应该切换到URLSessionConfiguration.default吗？

标签： swift5ios14xcode12bgtaskscheduler