Composite Design Pattern

This article is showing how to build the Composite Design Pattern using C#

This pattern know as a tree structure of simple and composite objects. Once again I grab the content from here http://www.dofactory.com/net/composite-design-pattern.

At first we look at the diagram, the logical model.

clip_image001

 

Firstly, create a Component Class. This class declares the interface for objects in the composition, implements default behavior for the interface common to all classes, as appropriate, and declares an interface for accessing and managing its child components. This class may defines an interface for accessing a component’s parent in the recursive structure, and implements it if that’s appropriate.

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);

}

 

Second class a Leaf class inherit from Component class. This class represents leaf objects in the composition. A leaf has no children and it defines behavior for primitive objects in the composition.

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);

    }

}

 

Thirdly, create a Composite class inherit from Component. This class defines behavior for components having children and stores child components. It implements child-related operations in the Component interface.

class Composite : Component

{

    private List<Component> _children = new List<Component>();

 

    // Constructor

    public Composite(string name)

        : base(name)

    {

    }

 

    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);

        }

    }

}

 

Finally, the main program, we can treat this as a client because it manipulates objects in the composition through the Component interface.

 

static void Main()

{

    // Create a tree structure

    Composite root = new Composite(“root”);

    root.Add(new Leaf(“Leaf A”));

    root.Add(new Leaf(“Leaf B”));

 

    Composite comp = new Composite(“Composite X”);

    comp.Add(new Leaf(“Leaf XA”));

    comp.Add(new Leaf(“Leaf XB”));

 

    root.Add(comp);

    root.Add(new Leaf(“Leaf C”));

 

    // Add and remove a leaf

    Leaf leaf = new Leaf(“Leaf D”);

    root.Add(leaf);

    root.Remove(leaf);

 

    // Recursively display tree

    root.Display(1);

 

    // Wait for user

    Console.ReadKey();

}

You can also download a single solution from http://skydrive.live.com. The sample file name is ConAppComposite.zip. My MSN ID is chanmmn@hotmail.com.

About chanmingman

Since March 2011 Microsoft Live Spaces migrated to Wordpress (http://www.pcworld.com/article/206455/Microsoft_Live_Spaces_Moves_to_WordPress_An_FAQ.html) till now, I have is over 1 million viewers. This blog is about more than 50% telling you how to resolve error messages, especial for Microsoft products. The blog also has a lot of guidance teaching you how to get stated certain Microsoft technologies. The blog also uses as a help to keep my memory. The blog is never meant to give people consulting services or silver bullet solutions. It is a contribution to the community. Thanks for your support over the years. Ming Man is Microsoft MVP since year 2006. He is a software development manager for a multinational company. With 25 years of experience in the IT field, he has developed system using Clipper, COBOL, VB5, VB6, VB.NET, Java and C #. He has been using Visual Studio (.NET) since the Beta back in year 2000. He and the team have developed many projects using .NET platform such as SCM, and HR based applications. He is familiar with the N-Tier design of business application and is also an expert with database experience in MS SQL, Oracle and AS 400.
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