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      1. 如何为具有空目标的实例方法创建委托?

        时间:2023-11-11

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                • 本文介绍了如何为具有空目标的实例方法创建委托?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着跟版网的小编来一起学习吧!

                  问题描述

                  我注意到 Delegate 类有一个 Target 属性,它(大概)返回委托方法将在其上执行的实例.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
                      }
                  }
                  

                  调用它时,我想做类似的事情:

                  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);
                      }
                  }
                  

                  但是当我尝试构造委托时,我得到了一个 ArgumentException(实例方法的委托不能有 null 'this').我想做的事是否可行,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

                  啊哈!找到了!

                  您可以使用 CreateDelegate 重载,使用带有隐式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);
                      }
                  }
                  

                  这篇关于如何为具有空目标的实例方法创建委托?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持跟版网!

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