关于 ios：即使在我的操作在 main 方法中完成之前，也会触发完成块


Completion block is getting triggered even before my operation completes in main method

我正在尝试使用 OperationQueue 和 Operation 在 Firebase 中创建用户。我将 Firebase Auth 调用放在操作主方法中。即使在 Firebase 注册过程成功之前，也会触发操作的完成块。

RegistrationViewModal.swift

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//This is operation initialization
 let operationQueues = OperationQueues()
 let registrationRecord = RegistrationRecord(user: self.user!, encryptedData: self.fireBaseAuthCompliance)
 let userRegistrationOperation = UserRegistrationOperation(registrationRecord: registrationRecord)
            userRegistrationOperation.completionBlock = {
//I am expecting this completion block will be called only when my firebase invocation in main() method is finished
   DispatchQueue.main.async {
//Since this block is getting triggered even before completion, the //value is returning as null
     self.user?.uid = userRegistrationOperation.registrationRecord.user.uid

                }
            }
     operationQueues.userRegistrationQueue.addOperation(userRegistrationOperation)

UserRegistrationOperation.swift

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class OperationQueues {
    lazy var userRegistrationQueue: OperationQueue = {
        var queue = OperationQueue()
        queue.maxConcurrentOperationCount = 1
        queue.name ="User registration queue"
        return queue
    }()
}

class UserRegistrationOperation: Operation {
    var registrationRecord: RegistrationRecord

    init(registrationRecord: RegistrationRecord) {
        self.registrationRecord = registrationRecord
    }
    override func main() {

        guard !isCancelled else { return }
        self.registrationRecord.state = RegistrationStatus.pending
//Firebase invocation to create a user in Firebase Auth
        Auth.auth().createUser(withEmail: self.registrationRecord.user.userEmail, password: self.registrationRecord.encryptedData){ [weak self](result, error) in
            if error != nil {
                print("Error occured while user registration process")
                self?.registrationRecord.state = RegistrationStatus.failed

                return
            }
            self?.registrationRecord.user.uid = result?.user.uid
            self?.registrationRecord.state = RegistrationStatus.processed

        }
    }

}

问题是你的操作正在启动一个异步进程，但是在异步任务启动时操作完成，而不是在异步任务完成时完成。

你需要做与a€?concurrenta€?相关的KVO？操作，如文档中所述：

If you are creating a concurrent operation, you need to override the following methods and properties at a minimum:

  • start()
  • isAsynchronous
  • isExecuting
  • isFinished

In a concurrent operation, your start() method is responsible for starting the operation in an asynchronous manner. Whether you spawn a thread or call an asynchronous function, you do it from this method. Upon starting the operation, your start() method should also update the execution state of the operation as reported by the isExecuting property. You do this by sending out KVO notifications for the isExecuting key path, which lets interested clients know that the operation is now running. Your isExecuting property must also provide the status in a thread-safe manner.

Upon completion or cancellation of its task, your concurrent operation object must generate KVO notifications for both the isExecuting and isFinished key paths to mark the final change of state for your operation. (In the case of cancellation, it is still important to update the isFinished key path, even if the operation did not completely finish its task. Queued operations must report that they are finished before they can be removed from a queue.) In addition to generating KVO notifications, your overrides of the isExecuting and isFinished properties should also continue to report accurate values based on the state of your operation.

现在所有这些听起来都令人毛骨悚然，但实际上并没有那么糟糕。一种方法是编写一个处理所有这些 KVO 内容的基本操作类，这个答案概述了一个示例实现。

然后你可以继承AsynchronousOperation，并确保在任务完成时调用finish(或任何触发isFinished KVO)：

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class UserRegistrationOperation: AsynchronousOperation {
    var registrationRecord: RegistrationRecord

    init(registrationRecord: RegistrationRecord) {
        self.registrationRecord = registrationRecord
        super.init()                                // whenever you subclass, remember to call `super`
    }

    override func main() {    
        self.registrationRecord.state = .pending

        //Firebase invocation to create a user in Firebase Auth

        Auth.auth().createUser(withEmail: registrationRecord.user.userEmail, password: registrationRecord.encryptedData) { [weak self] result, error in
            defer { self?.finish() }                // make sure to call `finish` regardless of how we leave this closure

            guard let result = result, error == nil else {
                print("Error occured while user registration process")
                self?.registrationRecord.state = .failed    
                return
            }

            self?.registrationRecord.user.uid = result.user.uid
            self?.registrationRecord.state = .processed
        }
    }
}

有很多方法可以实现 AsynchronousOperation 类，这只是一个例子。但是一旦你有了一个很好地封装了并发操作 KVO 的类，你就可以对它进行子类化，并且你可以编写自己的并发操作，只需对代码进行很少的更改。