如何创建指向另一个 Action C# 的 Action？

Question

我运行在 c# 中遇到了一些意外行为。我基本上是在尝试将一个动作分配给另一个动作的 reference，这样我以后就可以 subscribe/unsubcrib 方法对引用的动作。我不想知道实现引用操作的 class。

问题是，应该指向我想听的动作的动作似乎并没有真正指向它。我认为只要引用的操作被引发，它就会引发，但显然事实并非如此。

我可能对代表有一些误解。有人可以告诉我我做错了什么吗？有没有解决我想要实现的目标的方法？

感谢任何回复！

public class WaitForActionProcess : IProcess
{
    public Action Finished { get; set; }
    Action actionHandler;

    public WaitForActionProcess(ref Action action)
    {
        actionHandler = action;
    }

    public void Play()
    {
        actionHandler += RaiseFinished;
    }

    public void RaiseFinished()
    {
        actionHandler -= RaiseFinished;

        if(Finished != null)
        {
            Finished();
        }
    }
}

使用示例：

public class ReturnToMainMenuFrame : TutorialEventFrame
{
    [SerializeField]
    TutorialDialogueData dialogueData;

    [SerializeField]
    PointingArrowData arrowData;

    [SerializeField]
    TutorialDialogue tutorialDialogue;

    [SerializeField]
    PointingArrow arrow;

    [SerializeField]
    MainView mainView;

    public override void StartFrame()
    {
        frameProcesses.Add(new ShowPointToUIProcess(arrow, arrowData));
        frameProcesses.Add(new ShowDialogueProcess(tutorialDialogue, dialogueData));
        frameProcesses.Add(new WaitForActionProcess(ref mainView.OnViewShown));
        frameProcesses.Add(new HideDialogueProcess(tutorialDialogue, this));
        frameProcesses.Add(new HidePointToUIProcess(arrow,this));
        base.StartFrame();
    }

}

框架基础实现：

public class TutorialEventFrame : MonoBehaviour {

    public delegate void OnFrameEnded();
    public event OnFrameEnded FrameEnded;

    public List<IProcess> frameProcesses = new List<IProcess>();

    public bool debugMode = false;

    public virtual void StartFrame()
    {
        StartProcess(0);
    }

    void StartProcess(int processIndex)
    {
        if (processIndex < frameProcesses.Count)
        {
            int nextProcessIndex = processIndex + 1;
            frameProcesses[processIndex].Finished += () => StartProcess(nextProcessIndex);
        }
        else
        {
            EndFrame();
            return;
        }

        if (debugMode)
        {
            Debug.Log("Starting process: " + frameProcesses[processIndex] + " of processes: " + (processIndex + 1) + "/" + (frameProcesses.Count - 1) + " on frame: " + name);
        }

        frameProcesses[processIndex].Play();           
    }

    public virtual void EndFrame() {

        foreach (var process in frameProcesses)
        {
            process.Finished = null;
        }

        if (debugMode)
        {
            Debug.Log("frame: " + name + " finished");
        }
        frameProcesses.Clear();

        if (FrameEnded != null) {
            FrameEnded();
        }
    }
}

Answer 1

假设 OnViewShown 是一个事件，你想在调用 Play 时开始监听这个事件，然后在事件触发时调用 Finished，下面将允许你这样做：

public class WaitForActionProcess : IProcess
{
    public Action Finished { get; set; }

    Action<Action> Subscribe { get; }
    Action<Action> Unsubscribe { get; }

    public WaitForActionProcess(Action<Action> subscribe, Action<Action> unsubscribe)
    {
        Subscribe = subscribe;
        Unsubscribe = unsubscribe;
    }

    public void Play()
    {
        Subscribe(RaiseFinished);
    }

    public void RaiseFinished()
    {
        Unsubscribe(RaiseFinished);
        Finished?.Invoke();
    }
}

调用方式：

 var wfap = new WaitForActionProcess(
       h => mainView.OnViewShown += h, 
       h => mainView.OnViewShown -= h);

请注意，您希望 100% 确定 OnViewShown 将在播放后触发，否则将永远不会调用 Finished，并且您还会遇到内存泄漏，因为您从未取消订阅该事件。

尽管您可能无法在 Unity 中使用它，但请查阅 System.Reactive，它使此类事情形式化并使事件处理更易于管理。

Answer 2

简答

how to make an action that points to another action c#?

你不能。动作是委托，委托是不可变的。

the action that should be pointing to the action I want to listen to doesn't seem to actually point to it.

那是因为 delegates 是不可变的。即使您传递了委托的 ref，当您执行分配时，您也会创建一个副本。代表就像 strings 那样。

public WaitForActionProcess(ref Action action)
{
    // assignment creates a copy of a delegate
    actionHandler = action;
}

例子

这里a Fiddle for you进一步说明。

public class Program
{
    static Action action1;
    static Action actionHandler;
    public static void Main()
    {
        WaitForActionProcess(ref action1);
    }

    public static void WaitForActionProcess(ref Action action)
    {
        // this is still a reference to action1
        action += Both;

        // assignment creates a copy of a delegate
        actionHandler = action;

        // action is still a reference to action1
        // but actionHandler is a *copy* of action1
        action += OnlyAction1;
        actionHandler += OnlyActionHandler;

        action();
        // Both
        // OnlyAction1

        actionHandler();
        // Both
        // OnlyAction2
    }

    public static void Both()=> Console.WriteLine("Both");
    public static void OnlyAction1() => Console.WriteLine("OnlyAction1");
    public static void OnlyActionHandler() => Console.WriteLine("OnlyActionHandler");
}

可能的解决方法

改用 List<Action>。 Here it is as a Fiddle.

using System;
using System.Collections.Generic;

public class Program
{
    static List<Action> action1 = new List<Action>();
    static List<Action> actionHandler;
    public static void Main()
    {
        WaitForActionProcess(action1);
    }

    public static void WaitForActionProcess(List<Action> action)
    {
        action.Add(Both);

        // assignment passes a reference to the List
        actionHandler = action;

        action.Add(OnlyAction1);
        actionHandler.Add(OnlyActionHandler);

        // now things work nicely
        foreach(var a in action) a();
        foreach(var a in actionHandler) a();
    }

    public static void Both()=> Console.WriteLine("Both");
    public static void OnlyAction1() => Console.WriteLine("OnlyAction1");
    public static void OnlyActionHandler() => Console.WriteLine("OnlyActionHandler");
}

如何创建指向另一个 Action C# 的 Action？

how to make an Action that points to another Action C#?

c#

delegates

pointers

action

ref

简答

例子

可能的解决方法