BGTaskScheduler失败，原因是不存在具有标识符的后台任务，或者该任务可能已结束

Question

使用iOS 13.3.1 Xcode 11.3.1 Swift 5

代码这样说，编译，但不能正确运行。当我后台我的应用程序时，我得到一条错误消息，说“失败，没有后台任务存在，标识符为1或它可能已经结束”。

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
// Override point for customization after application launch.
BGTaskScheduler.shared.register(forTaskWithIdentifier: "ch.blah.refresh", using: nil) { (task) in
  self.handleAppRefresh(task: task as! BGAppRefreshTask)
}


return true
}

func applicationDidEnterBackground(_ application: UIApplication) {
  scheduleAppRefresh()
}

var request: BGAppRefreshTaskRequest!

func scheduleAppRefresh() {
  request = BGAppRefreshTaskRequest(identifier: "ch.blah.refresh")
  request.earliestBeginDate = Date(timeIntervalSinceNow: 60)
do {
  try BGTaskScheduler.shared.submit(request)
} catch {
  print("Could not schedule app refresh: \(error)")
}

}

func handleAppRefresh(task: BGAppRefreshTask) {
 scheduleAppRefresh()

 let queue = OperationQueue()
 queue.maxConcurrentOperationCount = 1

 queue.addOperation {
   for i in 1 ... 1000000 {
    print("\(i)")
   }
 }

 let lastOp = queue.operations.last
 lastOp?.completionBlock = {
   task.setTaskCompleted(success: !lastOp!.isCancelled)
 }

 task.expirationHandler = {
   queue.cancelAllOperations()
 }


 }

是的，我确实添加了Info.plist的密钥

<key>BGTaskSchedulerPermittedIdentifiers</key>
<array>
    <string>ch.blah.refresh</string>
</array> 

由于iOS 13，我收到了几个故障。我遗漏了什么？

我确实尝试过下载Apple WWDC代码来看一下。但它似乎也有同样的问题。

Answer 1

试试这个：

let queue = OperationQueue.main