无法转换继承的泛型？

发布于 2024-12-13 10:08:28 字数 705 浏览 1 评论 0原文

我正在尝试以下方法，但它给了我一个编译器错误：

public class MyManager<T> : where T:MyEventArgs
{
    private Dictionary<EventHandler<T>, EventFilter<T>> m_cSubscriptions;

    public void Subscribe<K>(EventHandler<K> _cHandler, EventFilter<K> _cFilter)
    where K:T
    {
        try
        {
            // cannot convert EventHandler<K> to EventHandler<T>
            m_cSubscriptions.Add(_cHandler, _cFilter);
        }
        catch (ArgumentException)
        {
            m_cSubscriptions[_cHandler] = _cFilter;
        }
    }
}

问题：为什么我不能将处理程序从 K 转换为 T？

我使用的是.net 2.0，因为我使用的是Unity3D。我必须自己投吗？我读过有关协变和逆变的内容，但我无法理解这一点。

原文

I am trying the following method, but it gives me a compiler error:

public class MyManager<T> : where T:MyEventArgs
{
    private Dictionary<EventHandler<T>, EventFilter<T>> m_cSubscriptions;

    public void Subscribe<K>(EventHandler<K> _cHandler, EventFilter<K> _cFilter)
    where K:T
    {
        try
        {
            // cannot convert EventHandler<K> to EventHandler<T>
            m_cSubscriptions.Add(_cHandler, _cFilter);
        }
        catch (ArgumentException)
        {
            m_cSubscriptions[_cHandler] = _cFilter;
        }
    }
}

Question: Why can't I convert the handler from K to T?

I am using a .net 2.0, because I am using Unity3D. Do I have to cast it myself? I have read about covariance and contravariance, but I couldn't make sense of this one.

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所谓喜欢 2024-12-20 10:08:28

EventHandler 不是 EventHandler。输入参数是逆变的。所以你的代码也无法在 C#4/.net 4 中工作。

您可以通过创建包装器来解决此问题（此示例仅适用于 C#3，但 C#2 也可以使用类似的代码）：

(s,e) => handler(s, (K)e)

但是，您会因此失去静态类型安全性。

要以安全的方式转换委托，您可以使用我的 ConvertDelegate< ;T> 方法。

An EventHandler<Derived> is no EventHandler<Base>. Input parameters are contra-variant. So your code wouldn't work in C#4/.net 4 either.

You can work around this by creating a wrapper (This example only works with C#3, but similar code is possible with C#2):

(s,e) => handler(s, (K)e)

But you lose static type safety with this cast.

To convert delegates in the safe direction you can use my ConvertDelegate<T> method.

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像你 2024-12-20 10:08:28

我决定使用 Delegate 将字典更改为更常见的字典，并定义一个不带泛型的普通 EventFilter 类。我希望演员阵容是正确的，因为我还没有测试过。我希望它会起作用。

public class MyManager<T> : where T:MyEventArgs
{
    private Dictionary<Delegate, EventFilter> m_cSubscriptions;

    public void Subscribe<K>(EventHandler<K> _cHandler, EventFilter<K> _cFilter)
    where K:T
    {
        try
        {
            // cannot convert EventHandler<K> to EventHandler<T>
            m_cSubscriptions.Add(_cHandler, _cFilter);
        }
        catch (ArgumentException)
        {
            m_cSubscriptions[_cHandler] = _cFilter;
        }
    }
}

I've decided to change the dictionary to a more common one by using Delegate and also defining a normal EventFilter class without generics. I hope that the casting will be correct, since I haven't tested this yet. I hope that it will work.

public class MyManager<T> : where T:MyEventArgs
{
    private Dictionary<Delegate, EventFilter> m_cSubscriptions;

    public void Subscribe<K>(EventHandler<K> _cHandler, EventFilter<K> _cFilter)
    where K:T
    {
        try
        {
            // cannot convert EventHandler<K> to EventHandler<T>
            m_cSubscriptions.Add(_cHandler, _cFilter);
        }
        catch (ArgumentException)
        {
            m_cSubscriptions[_cHandler] = _cFilter;
        }
    }
}

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