使用C ++ / CLI或C＃实现状态设计模式

Question

I am trying to implement the state design pattern using C++/CLI. This pattern requires that the State class be a friend of the Context. But C++/CLI does not allow a friend class. I understand that this is also the case with C#. Has anyone implemented the state pattern with C++/CLI or C#? I would like to know how you got around the absence of friend class.

Answer 1

Having the State class be a friend of the Context class is not a requirement for implementing the State pattern. Wikipedia has an implementation without using the friend modifier.

Answer 2

Its done using Association (or what all the cool kids are calling Dependency Injection). Inject the state into the context. See the implementation on DoFactory

Answer 3

You could keep state in a subclass, then replace sub class object with a different inheriting type when state changes.

class YourClass
{
  private MyEnum _myStateEnum; // Wrap this with a public property
  private MyInnerClass _myStateLogic; // Change this with appropriate type when above changes

  public void AnExampleMethod()
  {
      _myStateLogic.AnExampleMethod();
  }

  internal abstract class MyInnerClass
  {
      public virtual abstract void AnExampleMethod();
  }

  internal class MyOtherInnerClass1: MyInnerClass
  {
      public override void AnExampleMethod() { }
  }

  internal class MyOtherInnerClass2: MyInnerClass
  {
      public override void AnExampleMethod() { }
  }
}