如何创建具有null目标的实例方法的委托？ [英] How to create a delegate to an instance method with a null target?

问题描述

我注意到Delegate类有一个Target属性，（假定）返回委托方法将执行的实例。我想做这样的事情：

I've noticed that the Delegate class has a Target property, that (presumably) returns the instance the delegate method will execute on. I want to do something like this:

void PossiblyExecuteDelegate(Action<int> method)
{
    if (method.Target == null)   
    {
        // delegate instance target is null
        // do something
    }
    else
    {
         method(10);
         // do something else
    }
}

我想做一些类似的事情：

When calling it, I want to do something like:

class A
{
    void Method(int a) {}

    static void Main(string[] args)
    {
        A a = null;
        Action<int> action = a.Method;
        PossiblyExecuteDelegate(action);
    }
}

但是我得到一个ArgumentException（代理到一个实例方法当我尝试构造代理时，不能有一个null'this'）。是我想做的可能，我该怎么做？

But I get an ArgumentException (Delegate to an instance method cannot have a null 'this') when I try to construct the delegate. Is what I want to do possible, and how can I do it?

推荐答案

Ahah！ 发现！

您可以使用 CreateDelegate 重载，使用明确指定的隐式this第一个参数的委托：

You can create an open instance delegate using a CreateDelegate overload, using a delegate with the implicit 'this' first argument explicitly specified:

delegate void OpenInstanceDelegate(A instance, int a);

class A
{
    public void Method(int a) {}

    static void Main(string[] args)
    {
        A a = null;
        MethodInfo method = typeof(A).GetMethod("Method");
        OpenInstanceDelegate action = (OpenInstanceDelegate)Delegate.CreateDelegate(typeof(OpenInstanceDelegate), a, method);

        PossiblyExecuteDelegate(action);
    }
}

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