C# 設計模式：合成模式完整指南（三）— 透明式合成模式結構與實作

透明式合成模式特點

所有構件類別（無論葉節點/合成節點）**均符合固定介面**，包含 Add/Remove/GetChild 等管理方法。

結構圖

三大角色

完整代碼實作

using System;
using System.Text;
using System.Collections;

abstract class Component
{
    protected string name;
    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);
}

class Composite : Component
{
    private ArrayList children = new ArrayList();
    public Composite(string name) : base(name) { }

    public override void Add(Component c) => children.Add(c);
    public override void Remove(Component c) => children.Remove(c);

    public override void Display(int depth)
    {
        Console.WriteLine(new string('-', depth) + name);
        foreach (Component c in children) c.Display(depth + 2);
    }
}

class Leaf : Component
{
    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 class Client
{
    public static void Main()
    {
        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"));

        Leaf l = new Leaf("Leaf D");
        root.Add(l);
        root.Remove(l);

        root.Display(1);
    }
}

透明式 vs 安全式對比

選擇建議

• 客戶端統一處理所有節點 → 透明式
• 嚴禁對葉節點調用管理方法 → 安全式
• 現代 C# 可用介面隔離：IComponent + IComposite : IComponent 實現編譯時安全與介面統一並存