swift - 请求 GKStateMachine 的简单示例？

Question

我一直在研究 Apple 的 Swift 状态机并找到了几个示例，但没有一个真正简单到死。

有人可以在 Swift 中创建一个 super 简单的 GKStateMachine，也许有两个状态，最好是全部在一个 Swift 文件中吗？谢谢!

Answer 1

这是在美国工作的交通信号灯状态机示例。交通灯从 green -> yellow -> red -> green 移动。

在应用程序中，您可能有 didEnter(from:) 例程更新屏幕上的图形，或允许其他 Actor 移动。

import UIKit
import GameKit

class Green: GKState {

    override func isValidNextState(_ stateClass: AnyClass) -> Bool {
        return stateClass is Yellow.Type
    }

    override func didEnter(from previousState: GKState?) {
        print("Traffic light is green")
    }
}

class Yellow: GKState {
    override func isValidNextState(_ stateClass: AnyClass) -> Bool {
        return stateClass is Red.Type
    }

    override func didEnter(from previousState: GKState?) {
        print("Traffic light is yellow")
    }

}

class Red: GKState {
    override func isValidNextState(_ stateClass: AnyClass) -> Bool {
        return stateClass is Green.Type
    }

    override func didEnter(from previousState: GKState?) {
        print("Traffic light is red")
    }
}

class ViewController: UIViewController {

    var stateMachine: GKStateMachine?

    override func viewDidLoad() {
        super.viewDidLoad()

        // Create the states            
        let green = Green()
        let yellow = Yellow()
        let red = Red()

        // Initialize the state machine            
        stateMachine = GKStateMachine(states: [green, yellow, red])

        // Try entering various states...            
        if stateMachine?.enter(Green.self) == false {
            print("failed to move to green")
        }
        if stateMachine?.enter(Red.self) == false {
            print("failed to move to red")
        }
        if stateMachine?.enter(Yellow.self) == false {
            print("failed to move to yellow")
        }
        if stateMachine?.enter(Green.self) == false {
            print("failed to move to green")
        }
        if stateMachine?.enter(Red.self) == false {
            print("failed to move to red")
        }

    }

}

输出:

Traffic light is green
failed to move to red
Traffic light is yellow
failed to move to green
Traffic light is red