如何创建一个委托实例方法与空目标? [英] How to create a delegate to an instance method with a null target?
问题描述
我已经注意到,委托类有一个目标属性,即(presumably)返回实例的委托方法将执行上。我想要做这样的事情:
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
}
}
在调用它,我想做的事情是这样的:
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);
}
}
不过,我得到一个ArgumentException(代表实例方法不能为空本),当我试图建立的委托。就是我想要做的可能,我该怎么办呢?
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! 找到了!
您可以使用 CreateDelegate 一>过载,使用委托与隐显式地指定这'第一个参数:
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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