当从外部进程的事件调用方法时，Unity 变量会消失

Question

我正在使用 Unity 和外部引擎（用 c# 编写的可执行文件）编写国际象棋 UI。我可以向流程（引擎）发送和接收数据。这是可行的，但是当调用 Make_Move 方法时，当进程返回数据时，就会出现问题。虽然调试代码执行只是在尝试访问 Make_Move 方法中的 Unity 对象时停止，并且缺少对象，即部分 gameObject 和 sprite，但其余变量（不是统一对象）仍然存在。我没有收到任何错误，所有变量都是一个类的一部分，该类保存在一个数组中，该数组跟踪它的精灵游戏对象以及其他东西。

为什么只有统一对象会从对象数组中消失？

为什么在尝试访问统一对象（精灵等）时代码执行停止？

如何解决这个问题？

用于发送和接收 4 位字符串的 Unity 类，移动的开始和结束位置 (xyxy)

public static class UCI
 {
     static Process process = new Process();
 
     static UCI()
     {
         ProcessStartInfo si = new ProcessStartInfo()
         {
             FileName = "ChessEngine.exe",
             UseShellExecute = false,
             CreateNoWindow = true,
             RedirectStandardError = true,
             RedirectStandardInput = true,
             RedirectStandardOutput = true
         };       
         process.StartInfo = si;  
 
         process.OutputDataReceived += new DataReceivedEventHandler(OnRecieved);
        
         process.Start();
         process.BeginErrorReadLine();
         process.BeginOutputReadLine();
     }
     public static void SendLine(string command)
     {
         Debug.Log("send: "+ command);
         process.StandardInput.WriteLine(command);
         process.StandardInput.Flush();
     }
     public static void Kill()
     {
         process.Kill();
     }  
     private static void OnRecieved(object sender, DataReceivedEventArgs e)
     {
         string text = e.Data;
        
         Debug.Log("Recieved: " + text);
         if(text.Length == 4)
             Game.Make_Move(new Move(Board.Squares[(int)char.GetNumericValue(text[0]),(int)char.GetNumericValue(text[1])],Board.Squares[(int)char.GetNumericValue(text[2]), (int)char.GetNumericValue(text[3])]));      
     }  
 }

出现问题的Unity make_Move方法：

static void Make_Move(Move move)
     {           
         var end = move.end.GetPiece();
 
         //posistion is a vector2Int, this line does not cause any trouble
         print("Pos: " + Squares[move.start.GetPosition().x, move.start.GetPosition().y].GetPosition());
         //this line causes execution to stop without error. if it is commented out execution will continue.
         print("obj: " + Squares[move.start.GetPosition().x, move.start.GetPosition().y].gameObject);
         //lines below this is not executed
 
         SetPiece(move.start.gameObject.GetComponent<Image>().sprite, move.end.GetPosition(), end.MoveCnt);      
         RemovePiece(move.start.GetPosition());
 
         // set the current turn to the other player 
         CurrentPlayer = CurrentPlayer == players[0] ? CurrentPlayer = players[1] : CurrentPlayer = players[0];            
     }

main scene chess board image

Answer 1

（大部分）Unity API 不能被后台线程使用！

我不知道您在 Squares 数组中使用/存储的类型但是：请注意，大多数 Unity API 直接影响或依赖于场景（例如任何变换属性，.gameObject 等）仅适用于 Unity 主线程！ （例外是例如简单的Vector3 操作，只要您不将它们分配给Transform）

我很确定这里的问题是您的 OnReceived 在不同的线程（启动的进程之一）上执行 => 您甚至在主线程中都看不到异常！

---

Unity 中经常使用的模式是所谓的“主线程调度程序”，可能看起来像例如

public class MainThreadDispatcher : MonoBehaviour
{
    // Here we store the current existing instance of this component
    private static MainThreadDispatcher _instance;

    // Public read-only access
    public static MainThreadDispatcher Instance => _instance;

    // A thread-safe Queue (first-in/first-out) for the actions
    // that shall be executed in the next Update call
    private readonly ConcurrentQueue<Action> _actions = new ConcurrentQueue<Action>();
    
    private void Awake ()
    {
        // Make sure only one instance of this exists (Singleton Pattern)
        if(_instance && _instance != this)
        {
            Destroy(gameObject);
            return;
        }

        _instance = this;

        // Optional but recommended: Make sure this object is not
        // destroyed if the scene is changed
        DontDestroyOnLoad (gameObject);
    }

    private void Update ()
    {
        // Run all actions that have been enqueued since the last frame
        while(_actions.TryDequeue(out var action)
        {
            action?.Invoke();
        }
    }

    // Call this from any thread to make an action be executed in the next Update call
    public void DoInMainThread(Action action)
    {
        // Simply add the action to the end of the thread-safe Queue
        _actions.Enqueue(action);
    }
}

那么你会在你的课堂上做

private static void OnRecieved(object sender, DataReceivedEventArgs e)
 {
     var text = e.Data;
    
     Debug.Log("Recieved: " + text);
     if(text.Length == 4)
     {
         MainThreadDispatcher.Instance.DoInMainThread(() =>
         {
             // Delay this code line until we are in the next unity main thread
             // "Update" call where Unity API can be safely used
             Game.MakeMove(new Move(Board.Squares[(int)char.GetNumericValue(text[0]),(int)char.GetNumericValue(text[1])],Board.Squares[(int)char.GetNumericValue(text[2]), (int)char.GetNumericValue(text[3])]));  
         });
     }    
 }  

现在您要做的就是确保在您的第一个场景中将MainThreadDispatcher 组件附加到任何始终处于活动状态的游戏对象。