C# Nested Class Access Parent Member [duplicate]

问题:

This question already has an answer here:

• What's the best way of accessing field in the enclosing class from the nested class? 8 answers

Is it possible to access a parent member in a child class...

class MainClass {
  class A { Whatever }

  class B {
    List<A> SubSetList;

    public void AddNewItem(A NewItem) {
       Check MasterListHere ????
    }
  }

  List<A> MasterList;
}

So... my main class will have a master list. It will also have a bunch of instances of B. In each instance of B, I want to add new A's to the particular B, but only if they exist in the Master List. I toyed with making the MasterList static and it works ... until I have more than one instance of MainClass... which I will have.

I could pass a reference to MasterList to each instance of B, but I will eventually have multiple of these "MasterLists" and i don't want to have to pass lots of references if i don't have to.

回答1:

You can use something like this:

class B {
    private MainClass instance;

    public B(MainClass instance)
    {
        this.instance = instance;
    }

    List SubSetList;

    public void AddNewItem(A NewItem) {
       Check MasterListHere ????
    }
  }

回答2:

In C# there is actually no implicit reference to the instance of the enclosing class, so you need to pass such a reference, and a typical way of doing this is through the nested class' constructor.

回答3:

With your definition, instances of class B may access the private methods and static fields of class MainClass.

回答4:

Regardless of whether you nest class B inside class A, any given instance of A will still need to know about the instance of B that it is held by. So you might want to initialize A with a reference to B and keep it in a field. This likely includes un-nesting it.

回答5:

Yes, but you would need to have a reference to the instance of MainClass from within you instance of B.

Have you thought of re-working your classes a little bit? Istead of having the AddNewItem method in B, you could have it in MainClass. That way it would be easy to check the MasterList from within MainClass.

回答6:

This might work for you:

public void AddNewItem(A newItem, Func<A, bool> checkForItemInMasterList)
{
    if (checkForItemInMasterList.Invoke(newItem)
        SubList.Add(newItem);
}

You would then have something in your MainClass to use the method like this:

public void AddItem(A newItem)
{
    new B().AddNewItem(newItem, x => MasterList.Contains(x));
}

To summarize it might look something like this:

class MainClass {
  class A { Whatever }

  class B {
    List<A> SubSetList;

    public void AddNewItem(A newItem, Func<A, bool> checkForItemInMasterList)
    {
        if (checkForItemInMasterList.Invoke(newItem)
            SubList.Add(newItem);
    }
  }

  //I don't know how you're adding items to instances of B.
  //This is purely speculative.
  public void AddItem(A newItem)
  {
      new B().AddNewItem(newItem, x => MasterList.Contains(x));
  }

  List<A> MasterList;
}