C＃泛型或反射 - 调用未知类的函数

Question

I'm making a game where workers perform actions based on a current Task . Each worker will be assigned a list of tasks, in a preferred order (which is influenced by the player's decisions).

When a task is completed (eg take item from X to Y), the worker needs to start a new task by checking through their list of possible tasks, see if each can be performed, and if so, set their current task to that task and start it (the last task - "Wander Around" is always going to be available).

I currently have this working using a big switch statement and Enums, but now want to generalise this code to create a Task class, and give the workers a list of preferred Tasks, a GetNextTask() function, and in the worker's Update() method, call currentTask.update() (this will get the worker to do whatever he's required to do under the current task, and which will call worker.GetNextTask() when the task is complete).

What I'm unclear on is the best way to store Tasks in the worker. Should I use:

1) Reflection. Store the possible Tasks as a list of types, then use reflection to a) call a static method public static virtual bool CanPerformThisTask() which is overridden in each subclass, and b) Create an instance of that task for the worker? (example attempt at code for this below - but unable to test yet)

2) Instantiate all the Tasks whenever a worker needs to get a new task (probably using Activator), and check (Task)task.CanPerformThisTask() for each one - if true, do that task. Instantiating them all seems inefficient though?

3) Generics. Can this be done using generics? If so, how?

Here is a snippet of my classes to give the idea of what I'm trying to do:

Worker Class:

protected List<Point> waypoints = new List<Point>();
public bool reachedDestination { get { return waypoints.Count == 0; } }
protected Task task;
public List<Type> possibleTasks;

public Worker(Task initialTask, List<Type> initialPossibleTasks ...)
: base(...)
{
     task = initialTask;
     possibleTasks = initialPossibleTasks;
}

public override void Update()
{
     base.Update();
     if (!reachedDestination) Move();
     task.Update();
}

public void GetNextTask()
{
    foreach (Type t in possibleTasks)
    {
        //reflection code here - will this work and can we do this with generics instead?
        Bool canDoT = (bool)t.GetMethod("CanPerformThisTask", BindingFlags.Static | BindingFlags.Public).Invoke(null, null);
        if (canDoT)
        {
            task = Activator.CreateInstance(t);
            return;
        }
    }
}

Here is some incomplete code for my base Task class (which shouldn't be instantiated):

public class Task
{
    public Worker worker;

    public virtual static bool CanPerformThisTask()
    {
        //never call this from here - always from subclasses
        return false;
    }

    public Task()
    {
        //set up code here
    }

    public virtual void Update()
    {
        //make worker do relevant activities here
        //call finish task when done
    }

    public void FinishTask()
    {
        worker.GetNextTask();
    }

}

and here is an example of a Task the worker will have in its list of possible tasks:

public class T_WorkerWander : Task
{

    public static override bool CanPerformThisTask()
    {
        //can always wander (other Tasks will have conditions here)
        return true;
    }

    public T_WorkerWander()
        : base()
    {
    }

    override public void Update()
    {
        //make the worker wander here
        if (worker.reachedDestination) FinishTask();
    }

}

---

Update: here is the code I've now got working

Task Class:

public abstract class Task
{
    //the entity holding this task
    public TaskableEntity taskEntity;

    public List<TaskStage> taskStages;
    public TaskStage currentTaskStage { get { return taskStages[0]; } }

    public Task(TaskableEntity t) { taskEntity = t; }

    /// <summary>
    /// the conditions for the Task to be started
    /// </summary>
    public virtual bool CanStart()
    {
        return true;
    }

    public void Start()
    {
        taskStages = new List<TaskStage>();
        InitialiseTaskStages();
        taskStages[0].Start();
    }

    public abstract void InitialiseTaskStages();

    public void Update()
    {
        currentTaskStage.Update();
        if (currentTaskStage.IsComplete()) TaskStageComplete();
    }

    public void TaskStageComplete()
    {
        taskStages.RemoveAt(0);
        if (taskStages.Count == 0) taskEntity.TaskComplete();
        else currentTaskStage.Start();
    }

    public void SetTaskStages(params TaskStage[] t)
    {
        taskStages = t.ToList();
    }

    public void Interrupt()
    {
        currentTaskStage.Interrupt();
    }

}

TaskStage class:

public sealed class TaskStage
{
    private Task task;

    private List<Point> pointsToMoveTo;
    public void SetPointsToMoveTo(Point p) { pointsToMoveTo = new List<Point>() { p }; }
    public void SetPointsToMoveTo(params Point[] p) { pointsToMoveTo = p.ToList(); }
    public void SetPointsToMoveTo(List<Point> p) { pointsToMoveTo = p; }
    public Action actionToApply;

    private float timeToWait;
    public void SetWait(float wait) { timeToWait = wait; }

    private IReservable[] itemsToReserve;
    public void SetItemsToReserve(params IReservable[] items) { itemsToReserve = items; }

    private IReservable[] itemsToUnreserve;
    public void SetItemsToUnreserve(params IReservable[] items) { itemsToUnreserve = items; }

    private Emotion emotionToSet;
    public void SetEmotionToSet(Emotion e) { emotionToSet = e; }

    private TaskStage _interrupt;
    public void SetInterruptAction(TaskStage t) { _interrupt = t; }
    public void Interrupt() { _interrupt.Start(); }

    public TaskStage(Task t)
    {
        task = t;
    }

    public void Start()
    {
        if (actionToApply != null) actionToApply();
        if (itemsToUnreserve != null) UnreserveItems();
        if (itemsToReserve != null) ReserveItems();
        if (pointsToMoveTo != null)
        {
            //this will need changing after pathfinding sorted out...
            if (pointsToMoveTo.Count == 1) task.taskEntity.SetWaypoints(pointsToMoveTo[0]);
            else task.taskEntity.waypoints = pointsToMoveTo;
        }
        if (emotionToSet != null) emotionToSet.StartEmotion();
    }

    public void Update()
    {
        if (timeToWait > 0) timeToWait -= GV.elapsedTime;
    }

    public bool IsComplete()
    {
        if (pointsToMoveTo != null && !task.taskEntity.reachedDestination) return false;
        if (timeToWait > 0) return false;
        return true;
    }

    public void ReserveItems()
    {
        foreach (IReservable i in itemsToReserve)
        {
            i.reserved = true;
        }
    }

    public void UnreserveItems()
    {
        foreach (IReservable i in itemsToUnreserve)
        {
            i.reserved = false;
        }
    }

}

Example Task:

public class T_WorkerGoToBed : Task
{
    public FactoryWorker worker { get { return taskEntity as FactoryWorker; } }
    public T_WorkerGoToBed(TaskableEntity t)
        : base(t) { }

    public override bool CanStart()
    {
        return Room.Available<Bed>(GV.Bedrooms);
    }

    public override void InitialiseTaskStages()
    {
        Bed bedToSleepIn = Room.NearestAvailableFurniture<Bed>(GV.Bedrooms, taskEntity.X, taskEntity.Y);

        //stage 1 - reserve bed and move there
        TaskStage ts1 = new TaskStage(this);
        ts1.SetItemsToReserve(bedToSleepIn);
        ts1.SetPointsToMoveTo(bedToSleepIn.XY);

        //stage 2 - sleep in bed
        TaskStage ts2 = new TaskStage(this);
        ts2.SetWait((worker.maxEnergy - worker.energy) / worker.energyRegeneratedPerSecondWhenSleeping);
        ts2.SetEmotionToSet(new E_Sleeping(worker, false));

        //stage 3 - unreserve bed
        TaskStage ts3 = new TaskStage(this);
        ts3.SetItemsToUnreserve(bedToSleepIn);
        ts3.SetEmotionToSet(new E_Happy(worker, false));

        SetTaskStages(ts1, ts2, ts3);
    }

}

Answer 1

It sounds like you need to reverse responsibility between task and worker. Instead of asking whether the task can be performed, ask the worker if he can perform a given task:

class Worker
{
    bool CanPerformTask<T>() where T : Task
    {
        var type = typeof(T);
        // code to determine whether worker can perform the task T             
    }

    // alternative with instance parameter
    bool CanPerformTask<T>( T task ) where T : Task
    {
        // code to determine whether worker can perform the task passed in
    }
}

This solution avoids the "instantiate all tasks or call static method" problem.

Also, consider using the built-in collection classes. Things such as queues and stacks can greatly simplify the code needed to schedule execution of things.

Answer 2

I think you are abusing the point of static classes. The "Task" class should be standard (not static). Your "Worker" class is not static therefore implying that there is more than one "Worker" instance. Given this paradigm, these workers can probably have the same task assigned to them.

Your "Worker" class needs to have this property modified from:

public List possibleTasks;

to

public List _possibleTasks;

You probably should not have public access to this property either. You can modify "CanPerformThisTask" as necessary.