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Composite

Composite en C#

Le Composite est un patron de conception structurel qui permet d’agencer les objets dans une structure ressemblant à une arborescence, afin de pouvoir la traiter comme un objet individuel.

Le composite est devenu la solution la plus populaire pour régler les problèmes d’une structure arborescente. Il offre une fonctionnalité très pratique qui permet de parcourir récursivement toute l’arborescence et d’additionner les résultats.

Complexité :

Popularité :

Exemples d’utilisation : Le composite est très répandu en C#. Il est souvent utilisé pour modéliser les hiérarchies des composants d’une interface utilisateur ou pour du code qui manipule des graphes.

Identification : Si vous avez une arborescence composée uniquement d’objets issus de la même hiérarchie de classes, c’est probablement un composite. Si les méthodes de ces classes délèguent les tâches aux objets enfants de l’arborescence et passent par une classe de base ou interface de la hiérarchie pour ce faire, il est très probable que ce soit réellement un composite.

Exemple conceptuel

Dans cet exemple, nous allons voir la structure du patron de conception Composite. Nous allons répondre aux questions suivantes :

  • Que contiennent les classes ?
  • Quel rôle jouent-elles ?
  • Comment les éléments du patron sont-ils reliés ?

Program.cs: Exemple conceptuel

using System;
using System.Collections.Generic;

namespace RefactoringGuru.DesignPatterns.Composite.Conceptual
{
    // The base Component class declares common operations for both simple and
    // complex objects of a composition.
    abstract class Component
    {
        public Component() { }

        // The base Component may implement some default behavior or leave it to
        // concrete classes (by declaring the method containing the behavior as
        // "abstract").
        public abstract string Operation();

        // In some cases, it would be beneficial to define the child-management
        // operations right in the base Component class. This way, you won't
        // need to expose any concrete component classes to the client code,
        // even during the object tree assembly. The downside is that these
        // methods will be empty for the leaf-level components.
        public virtual void Add(Component component)
        {
            throw new NotImplementedException();
        }

        public virtual void Remove(Component component)
        {
            throw new NotImplementedException();
        }

        // You can provide a method that lets the client code figure out whether
        // a component can bear children.
        public virtual bool IsComposite()
        {
            return true;
        }
    }

    // The Leaf class represents the end objects of a composition. A leaf can't
    // have any children.
    //
    // Usually, it's the Leaf objects that do the actual work, whereas Composite
    // objects only delegate to their sub-components.
    class Leaf : Component
    {
        public override string Operation()
        {
            return "Leaf";
        }

        public override bool IsComposite()
        {
            return false;
        }
    }

    // The Composite class represents the complex components that may have
    // children. Usually, the Composite objects delegate the actual work to
    // their children and then "sum-up" the result.
    class Composite : Component
    {
        protected List<Component> _children = new List<Component>();
        
        public override void Add(Component component)
        {
            this._children.Add(component);
        }

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

        // The Composite executes its primary logic in a particular way. It
        // traverses recursively through all its children, collecting and
        // summing their results. Since the composite's children pass these
        // calls to their children and so forth, the whole object tree is
        // traversed as a result.
        public override string Operation()
        {
            int i = 0;
            string result = "Branch(";

            foreach (Component component in this._children)
            {
                result += component.Operation();
                if (i != this._children.Count - 1)
                {
                    result += "+";
                }
                i++;
            }
            
            return result + ")";
        }
    }

    class Client
    {
        // The client code works with all of the components via the base
        // interface.
        public void ClientCode(Component leaf)
        {
            Console.WriteLine($"RESULT: {leaf.Operation()}\n");
        }

        // Thanks to the fact that the child-management operations are declared
        // in the base Component class, the client code can work with any
        // component, simple or complex, without depending on their concrete
        // classes.
        public void ClientCode2(Component component1, Component component2)
        {
            if (component1.IsComposite())
            {
                component1.Add(component2);
            }
            
            Console.WriteLine($"RESULT: {component1.Operation()}");
        }
    }
    
    class Program
    {
        static void Main(string[] args)
        {
            Client client = new Client();

            // This way the client code can support the simple leaf
            // components...
            Leaf leaf = new Leaf();
            Console.WriteLine("Client: I get a simple component:");
            client.ClientCode(leaf);

            // ...as well as the complex composites.
            Composite tree = new Composite();
            Composite branch1 = new Composite();
            branch1.Add(new Leaf());
            branch1.Add(new Leaf());
            Composite branch2 = new Composite();
            branch2.Add(new Leaf());
            tree.Add(branch1);
            tree.Add(branch2);
            Console.WriteLine("Client: Now I've got a composite tree:");
            client.ClientCode(tree);

            Console.Write("Client: I don't need to check the components classes even when managing the tree:\n");
            client.ClientCode2(tree, leaf);
        }
    }
}

Output.txt: Résultat de l’exécution

Client: I get a simple component:
RESULT: Leaf

Client: Now I've got a composite tree:
RESULT: Branch(Branch(Leaf+Leaf)+Branch(Leaf))

Client: I don't need to check the components classes even when managing the tree:
RESULT: Branch(Branch(Leaf+Leaf)+Branch(Leaf)+Leaf)

Composite dans les autres langues

Composite en C++ Composite en Go Composite en Java Composite en PHP Composite en Python Composite en Ruby Composite en Rust Composite en Swift Composite en TypeScript