¿Puede mezclar clases derivadas y bases en una lista genérica en C # de clase de base de tipo?

Question

¿Puede mezclar clases derivadas y basadas en una lista genérica en C # de clase de base de tipo?No veo por qué no ... y no veo una respuesta clara a esto ... pero jugando hoy con una lista genérica de tipo de clase base, que también tuvo en ella clases derivadas, no vi ningunaproblemas.Pero me pregunto si podría haber problemas potenciales, aparte de las limitaciones habituales de Upcast / Downcast que siempre son inherentes a las clases derivadas / basadas.La razón por la que pregunto: No sé si una lista genérica para C # funciona igual que lo que solía ser llamado un Lista de Array en C ++, es decir, si obtendrá ninguna queja durante la compilación para mezclar "tipos" como este (Base VS clases derivadas).Corrí numerosos ejemplos hoy sin quejarme, sino querer verificar si hay un potencial de un problema.

Answer 1

C # Los tipos de clase son tipos de referencia.Los tipos de clase C ++ se llamarían tipos de valor en el mundo .NET.La comparación adecuada sería una lista de C ++ de punteros de clase base, en la que podría almacenar un puntero a una clase derivada sin ningún problema.

Entonces, sí, está bien.

Answer 2

 using System;
 using System.Collections.Generic;

 namespace DoFactory.GangOfFour.Composite.Structural
{
/// <summary>
/// MainApp startup class for Structural 
/// Composite Design Pattern.  
/// </summary>
class MainApp
{
    /// <summary>
    /// Entry point into console application.
    /// </summary>
    static void Main()
    {
        // Create a tree structure
        Composite root = new Composite("root");
        root.Add(new Leaf("Leaf A")); //1st Add for root
        root.Add(new Leaf("Leaf B")); //2nd Add for root
        Console.WriteLine(" ....");
        root.Display(1);
        Console.WriteLine("...........");
        Composite comp = new Composite("Composite X");
        comp.Add(new Leaf("Leaf XA"));
        root.Add(comp); //add comp to root //3rd Add for root

        DerivedComposite myDerivedComposite = new DerivedComposite("derived member",      1000);
        Console.WriteLine("Show the special int, string for DerivedComposite");
        myDerivedComposite.mySpecialVariablesAre();
        Console.WriteLine("........");

        root.Add(myDerivedComposite); //4th Add for root

        Composite SecondRoot = new Composite("SecondRoot");
        SecondRoot.Add(new Leaf("Leaf fA"));


        SecondRoot.Add(myDerivedComposite); //add to SecondRoot

        root.Add(SecondRoot); //add comp to root ; //5th Add for root
        //// Recursively display tree again, after adding
        root.Display(1);

        Console.WriteLine("Now get List read back");
        Console.WriteLine("show List elements for root (should be five)");
        root.DisplayList();

        Console.WriteLine("Show List elements for comp (should be one)");
        comp.DisplayList();
        Console.WriteLine("Show List ele for SecondRoot (should be 2)");
         SecondRoot.DisplayList();

        // Wait for user
        Console.ReadKey();
    }
}


/// <summary>
/// The 'Component' abstract class
/// </summary>
abstract class Component
{
    protected string name;

    // Constructor
    public Component(string name)
    {
        this.name = name;
    }

    public abstract void Add(Component c);
    public abstract void Remove(Component c);
    public abstract void Display(int depth);
    public abstract void printSpecialInt();
}

/// <summary>
/// The 'Composite' class
/// </summary>
class Composite : Component
{
    private List<Component> _children = new List<Component>(); 
    //This Generic List was potentially troublesome but it executed fine
    protected int specialbaseInt;
    // Constructor
    public Composite(string name)
        : base(name)
    {
        specialbaseInt = -1;
    }

    public override void Add(Component component)
    {
        _children.Add(component);
    }

    public override void Remove(Component component)
    {
        _children.Remove(component);
    }

    public override void Display(int depth)
    {
        Console.WriteLine(new String('-', depth) + name);

        // Recursively display child nodes
        foreach (Component component in _children)
        {
            component.Display(depth + 2); //calls .Display again, is recursive
        }
    }

    public void DisplayList()
    {
        int ijk = _children.Count;
        Console.WriteLine("# elements in this List: {0}", ijk);
        foreach (Component c in _children)
        {
            int ii = c.GetHashCode();
            Type type = c.GetType();
            Console.WriteLine("GetHashCode, Type on list: {0}, {1}", ii, type.FullName);

            c.printSpecialInt();

        }
    }

    public override void printSpecialInt()
    {
        Console.WriteLine("special int (at base class): {0}", specialbaseInt);
    }
}

class DerivedComposite : Composite
{
    public string myExtraString;
    public int mySpecialInt;

    public DerivedComposite(string name,int ianint)
        : base(name)
    {
        myExtraString = name;
        mySpecialInt = ianint + 10;
        specialbaseInt = ianint;
    }

    public void mySpecialVariablesAre()
    {
        Console.WriteLine("The string, int, specialbaseInt are!- {0}, {1}, {2}", myExtraString, mySpecialInt, specialbaseInt);
    }

    public override void printSpecialInt()
    {
        Console.WriteLine("The string, int, specialbaseInt are (at derived): {0}, {1},    {2}", myExtraString, mySpecialInt, specialbaseInt);
    }

}

/// <summary>
/// The 'Leaf' class
/// </summary>
class Leaf : Component
{
    // Constructor
    public Leaf(string name)
        : base(name)
    {
    }

    public override void Add(Component c)
    {
        Console.WriteLine("Cannot add to a leaf");
    }

    public override void Remove(Component c)
    {
        Console.WriteLine("Cannot remove from a leaf");
    }

    public override void Display(int depth)
    {
        Console.WriteLine(new String('-', depth) + name);
    }

    public override void printSpecialInt()
    {
        Console.WriteLine("at Leaf printSpecialInt");
    }
}

/// <summary>
/// The 'Leafail' class //try and make it fail
/// </summary>
class Leafail : Component
{
    // Constructor
    public Leafail(string name)
        : base(name)
    {
        myExtraString = "Hi, I am Leafail";
        mySpecialInt = 123;
    }

    public string myExtraString;
    public int mySpecialInt;

    public override void Add(Component c)
    {
        Console.WriteLine("Cannot add to a leafail");
    }

    public override void Remove(Component c)
    {
        Console.WriteLine("Cannot remove from a leafail");
    }

    public override void Display(int depth)
    {
        Console.WriteLine(new String('-', depth) + name);
    }

    public void mySpecialVariablesAre()
    {
        Console.WriteLine("The string, int are: {0}, {1}", myExtraString,mySpecialInt);
    }
    public override void printSpecialInt()
     {
         Console.WriteLine("at Leafail printSpecialInt");
     }
}


}