使用運行時設定的型別呼叫泛型方法并傳遞泛型委托引數-有解無憂

編輯：這是一個 Unity 2018.4 專案，它使用 Mono 的自定義版本。腳本運行時版本為“.NET 4.x Equivalent”，API 兼容級別為“.NET Standard 2.0”

我有一個使用泛型AddListener<T>和RemoveListener<T>接受EventDelegate<T>引數的方法的自定義事件系統。在代碼的其他地方，如果Type在運行時確定，我想使用適當型別的委托添加和洗掉偵聽器，并且只知道何時引發事件。我不需要知道事件附帶的任何有效負載。

<T>總是從特定的抽象基型別派生的可能毫無價值。

在下面的示例中，我在靜態類上有一個靜態泛型方法，該方法將泛型委托作為引數。我試圖Type在運行時呼叫泛型方法，我想將泛型委托Type作為引數傳遞。如果在編譯時沒有具有正確簽名的既定方法，這可能嗎？

具有泛型委托和接受委托作為引數的泛型方法的靜態類：

public static class GameEvent
{
   public delegate void EventDelegate<in T>(T e) where T : BaseEvent;

   public static void AddListener<T>(EventDelegate<T> listener) where T : BaseEvent
   {
      ...
   }

   public abstract class BaseEvent : EventArgs
   {
   }
}

Type 將始終派生自特定的基型別。

派生類示例：

public class CustomGameEvent : GameEvent.BaseEvent
{
   public CustomGameEvent(object a, object b) // Constructor has 0 or more parameters of unknown type.
   {
   }
}

上述設定運行良好，我有許多正在運行的自定義事件。

例如，在某些類方法中，我會添加一個偵聽器并實作一個用于接收事件的委托方法，

private void SomeMethod()
{
   GameEvent.AddListener<CustomGameEvent>(this.CustomGameEventHandler);
}

private void CustomGameEventHandler(CustomGameEvent e)
{
   ... // This works and I can access properties of `e`.
}

現在談談我的問題。

Elsewhere, I would like to call GameEvent.AddListner<T> using a Type determined at runtime, where Type is derived from GameEvent.BaseEvent, however I'm not sure what to pass as a parameter when invoking the method. That's where I'm stuck.

I setup a method that receives a GameEvent.BaseEvent parameter instead of the derived Type. Does it even make sense to have a method that accepts the base type when I'd like the delegate method to accept the derived type?

private Type type = typeof(CustomGameEvent); // Some type that inherits from BaseEvent.

private void GameEventHandler(GameEvent.BaseEvent e)
{
   // Do something here. Don't care that e is the base type.
   // I just want to know when the `Type` event was raised.
   // Accept any parameter that is derived from GameEvent.BaseEvent.
}

private void AddListener()
{
   var mi = typeof(GameEvent).GetMethod(nameof(GameEvent.AddListener));
   // -> void AddListener[T](EventDelegate`1)

   var miGeneric = mi?.MakeGenericMethod(type);
   // -> void AddListener[CustomGameEvent](EventDelegate`1)

   var delegateType = typeof(GameEvent.EventDelegate<>).MakeGenericType(type);
   // -> GameEvent EventDelegate`1[CustomGameEvent]

   var parameters = new object[] { (GameEvent.EventDelegate<GameEvent.BaseEvent>)this.GameEventHandler };
   miGeneric?.Invoke(null, parameters);
   // -> When "AddListener<CustomGameEvent>()" is invoked, it receives a 
   //    "GameEvent EventDelegate`1[GameEvent BaseEvent]" not a
   //    "GameEvent EventDelegate`1[CustomGameEvent]"
}

This works for the most part and does what I'd expect, because I'm explicitly casting the this.GameEventHandler to (GameEvent.EventDelegate<GameEvent.BaseEvent>) and passing that as a parameter. But I'd like to cast the parameter object to the type stored in delegateType, so that AddListener<CustomGameEvent>() actually receives an EventDelegate<CustomGameEvent> and not a EventDelegate<GameEvent.BaseEvent>. Is that possible, and if so, how?

Can GameEventHandler(GameEvent.BaseEvent e) even be used as the delegate method if the object was cast to EventDelegate<CustomGameEvent> or would the invoke fail due to the signature mismatch?

I've tried using Convert.ChangeType(), however that fails with InvalidCastException: Object must implement IConvertible..

   var parameters = new object[]
      {
         Convert.ChangeType(
            (GameEvent.EventDelegate<GameEvent.BaseEvent>)this.GameEventHandler,
            delegateType)
      };

I also tried using a generic static helper method CastInto<T>(object obj), but that didn't cast as I hoped it would.

private void AddListener()
{
   ... // delegateType is stored

   var miCastInto = this.GetType().GetMethod(nameof(CastInto)).MakeGenericMethod(delegateType);
   // -> EventDelegate`1 CastInto[EventDelegate`1](System.Object), but is that what
   //    I want? Should it be:  EventDelegate`1[CustomGameEvent]
   //       CastInto[EventDelegate`1[CustomGameEvent]](System.Object)

   object o1 = (GameEvent.EventDelegate<GameEvent.BaseEvent>)this.GameEventHandler;
   // -> GameEvent.EventDelegate<GameEvent.BaseEvent> ... as expected.

   object o2 = miCastInto.Invoke(null, new[] { o });
   // -> GameEvent.EventDelegate<GameEvent.BaseEvent> ... not <CustomGameEvent>.

   var parameters = new object[] { castedObject }; // <- Wrong parameter type.

   ...
}

public static T CastInto<T>(object obj)
{
   return (T)obj;
}

I'm not even sure if I should be trying to finesse the GameEventHandler(GameEvent.BaseEvent e) delegate to typeDelegate. If it can be converted would GameEventHandler(GameEvent.BaseEvent e) still be called when the event was raised?

I saw Delegate.CreateDelegate(), but I don't really understand if that should be used here or how it should be used.

無論建立什么委托，它也將GameEvent.RemoveListener<T>在以后的類似呼叫中使用（使用相同的Type），因此委托可能必須與類實體一起存盤，并且在以后使用時不會重新創建。我假設第二個委托創建將被視為不同的（與原始創建的參考不同）。

uj5u.com熱心網友回復：

您可以使用Delegate.CreateDelegate來創建特定Type物件的委托。

var delegateType = typeof(GameEvent.EventDelegate<>).MakeGenericType(type);
// -> GameEvent EventDelegate`1[CustomGameEvent]

var methodInfo = typeof(YourClass).GetMethod(
    "GameEventHandler", BindingFlags.NonPublic | BindingFlags.Instance);

var parameters = new object[] { 
    Delegate.CreateDelegate(delegateType, this, methodInfo) 
};

您在此處呼叫的多載會創建一個呼叫實體方法的委托。第二個引數指示您希望呼叫該方法的實體。

轉載請註明出處，本文鏈接：https://www.uj5u.com/qiye/311155.html

標籤：C＃统一3d 泛型类型代表

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