如何在Swift中继承NSOperation以将SKAction对象排队以进行串行执行？

Question

Rob为子类化NSOperation 提供了一个很好的Objective-C解决方案,以实现SKAction对象的串行排队机制.我在自己的Swift项目中成功实现了这一点.

import SpriteKit

class ActionOperation : NSOperation
{
    let _node: SKNode // The sprite node on which an action is to be performed
    let _action: SKAction // The action to perform on the sprite node
    var _finished = false // Our read-write mirror of the super's read-only finished property
    var _executing = false // Our read-write mirror of the super's read-only executing property

    /// Override read-only superclass property as read-write.
    override var executing: Bool {
        get { return _executing }
        set {
            willChangeValueForKey("isExecuting")
            _executing = newValue
            didChangeValueForKey("isExecuting")
        }
    }

    /// Override read-only superclass property as read-write.
    override var finished: Bool {
        get { return _finished }
        set {
            willChangeValueForKey("isFinished")
            _finished = newValue
            didChangeValueForKey("isFinished")
        }
    }

    /// Save off node and associated action for when it's time to run the action via start().
    init(node: SKNode, action: SKAction) {

    // This is equiv to ObjC:
    // - (instancetype)initWithNode(SKNode *)node (SKAction *)action
    // See "Exposing Swift Interfaces in Objective-C" at https://developer.apple.com/library/mac/documentation/Swift/Conceptual/BuildingCocoaApps/InteractingWithObjective-CAPIs.html#//apple_ref/doc/uid/TP40014216-CH4-XID_35

        _node = node
        _action = action
        super.init()
    }

    /// Add the node action to the main operation queue.
    override func start()
    {
        if cancelled {
            finished = true
            return
        }

        executing = true

        NSOperationQueue.mainQueue().addOperationWithBlock {
            self._node.runAction(self._action) {
                self.executing = false
                self.finished = true
            }
        }
    }
}

要使用ActionOperation,请在客户端类中实例化NSOperationQueue类成员:

var operationQueue = NSOperationQueue()

在init方法中添加以下重要行:

operationQueue.maxConcurrentOperationCount = 1; // disallow follow actions from overlapping one another

然后,当您准备好向其添加SKActions时,它们会连续运行:

operationQueue.addOperation(ActionOperation(node: mySKNode, action: mySKAction))

您是否需要在任何时候终止操作:

operationQueue.cancelAllOperations() // this renders the queue unusable; you will need to recreate it if needing to queue anymore actions

希望有所帮助!

Answer 1

根据该文件:

在自定义实现中,isExecuting只要操作对象的执行状态发生更改,就必须为键路径生成KVO通知.

在自定义实现中,isFinished只要操作对象的完成状态发生更改,就必须为键路径生成KVO通知.

所以我认为你必须:

override var executing:Bool {
    get { return _executing }
    set {
        willChangeValueForKey("isExecuting")
        _executing = newValue
        didChangeValueForKey("isExecuting")
    }
}

override var finished:Bool {
    get { return _finished }
    set {
        willChangeValueForKey("isFinished")
        _finished = newValue
        didChangeValueForKey("isFinished")
    }
}