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我创建了 2 个操作，比如说 CKModifySubscriptionsOperation。一个用于私有数据库，另一个用于共享数据库。我可以通过添加到 OperationQueue 来将它们排队，每个下一个都将在上一个完成块之后开始。

let operationQueue = OperationQueue()
operationQueue.maxConcurrentOperationCount = 1
// ...
operationQueue.addOperation(operation)

// Queued great but all subscriptions are created in private database

但我需要从不同的数据库中执行一些操作（获取、修改等），但仍需要将它们排队。这是我向数据库添加操作的方法。如何将它们放入单个队列但仍让它们分别进入所需的数据库？

container.privateCloudDatabase.add(operation)
container.sharedCloudDatabase.add(operation)

// Put subscriptions to correct databases but no queue
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1 回答 1

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我通过创建受控的自定义操作解决了这个目标。

现在我们可以像这样对云数据库特定的操作进行排队

let privateSubscriptionOperation = SubscriptionOperation(type: .private)
let sharedSubscriptionOperation = SubscriptionOperation(type: .shared)

operationQueue.addOperation(privateSubscriptionOperation)
operationQueue.addOperation(sharedSubscriptionOperation)

首先是父类

class CKDatabaseControlledOperation: Operation {
    
    let databaseType: DatabaseType
    let database: CKDatabase
    
    private var _finished = false
    private var _executing = false
    
    init(type: DatabaseType) {
        databaseType = type
        switch type {
        case .private:
            database = CKContainer.default().privateCloudDatabase
        case .shared:
            database = CKContainer.default().sharedCloudDatabase
        }
    }
    
    override var isExecuting: Bool {
        get {
            return !_executing
        }
        set {
            willChangeValue(forKey: "isExecuting") // This must match the overriden variable
            _executing = newValue
            didChangeValue(forKey: "isExecuting") // This must match the overriden variable
        }
    }
    
    override var isFinished: Bool {
        get {
            return _finished
        }
        set {
            willChangeValue(forKey: "isFinished") // This must match the overriden variable
            _finished = newValue
            didChangeValue(forKey: "isFinished") // This must match the overriden variable
        }
    }
    
    func stopOperation() {
        isFinished = true
        isExecuting = false
    }
    
    func startOperation() {
        isFinished = false
        isExecuting = true
    }

    enum DatabaseType: String {
        case `private` = "private-changes"
        case shared = "shared-changes"
    }
}

然后我们可以创建任何数据库操作（本示例中的订阅，但可以与任何操作一起使用）

class SubscriptionOperation: CKDatabaseControlledOperation {
    
    override func main() {
        startOperation() //Operation starts
        
        let subscription = CKDatabaseSubscription(subscriptionID: databaseType.rawValue)
        //...set any needed stuff like NotificationInfo
        
        let operation = CKModifySubscriptionsOperation(subscriptionsToSave: [subscription], subscriptionIDsToDelete: [])

        operation.modifySubscriptionsCompletionBlock = { [unowned self] subscriptions, subscriptionIDs, error in
            //Handle errors
            self.stopOperation() //Operation ends
        }
        
        database.add(operation)
    }
    
}
于 2020-08-19T08:10:45.710 回答