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C# 設計模式無廢話系列（六）：Builder 建造者模式

編輯：關於C#

意圖

將複雜構建與其表示分離，使相同構建過程可創建不同表示。

適用場景

電腦城裝機：銷售詢問配置→出裝機單→提貨備料→技術人員按固定流程組裝（鎖主板→裝 CPU→裝記憶體→接硬碟→裝顯卡）。每台電腦零件不同（高/低配），但組裝流程固定。將變化零件與穩定流程分離 → Builder 模式。

完整範例程式碼

using System;
using System.Collections.Generic;
using System.Text;
using System.Reflection;

namespace BuilderExemple
{
    class Program
    {
        static void Main(string[] args)
        {
            ComputerFactory factory = new ComputerFactory();
            ComputerBuilder office = new OfficeComputerBuilder();
            factory.BuildComputer(office);
            office.Computer.ShowSystemInfo();
            ComputerBuilder game = new GameComputerBuilder();
            factory.BuildComputer(game);
            game.Computer.ShowSystemInfo();
        }
    }
    class ComputerFactory
    {
        public void BuildComputer(ComputerBuilder cb)
        {
            Console.WriteLine($"\n>>>>>>>>>>>>>>>>>>Start Building {cb.Name}");
            cb.SetupMainboard();
            cb.SetupCpu();
            cb.SetupMemory();
            cb.SetupHarddisk();
            cb.SetupVideocard();
            Console.WriteLine($">>>>>>>>>>>>>>>>>>Build {cb.Name} Completed\n");
        }
    }
    abstract class ComputerBuilder
    {
        protected string name;
        public string Name { get => name; set => name = value; }
        protected Computer computer;
        public Computer Computer { get => computer; set => computer = value; }
        public ComputerBuilder() => computer = new Computer();
        public abstract void SetupMainboard();
        public abstract void SetupCpu();
        public abstract void SetupMemory();
        public abstract void SetupHarddisk();
        public abstract void SetupVideocard();
    }
    class OfficeComputerBuilder : ComputerBuilder
    {
        public OfficeComputerBuilder() => name = "OfficeComputer";
        public override void SetupMainboard() => computer.Mainboard = "Abit升技LG-95C 主板(Intel 945GC/LGA 775/1066MHz)";
        public override void SetupCpu() => computer.Cpu = "Intel 賽揚D 336 (2.8GHz/LGA 775/256K/533MHz)";
        public override void SetupMemory() => computer.Memory = "Patriot博帝DDR2 667 512MB";
        public override void SetupHarddisk() => computer.Harddisk = "Hitachi日立SATAII 80G/7200轉/8M";
        public override void SetupVideocard() => computer.Videocard = "主板集成";
    }
    class GameComputerBuilder : ComputerBuilder
    {
        public GameComputerBuilder() => name = "GameComputer";
        public override void SetupMainboard() => computer.Mainboard = "GIGABYTE技嘉GA-965P-DS3 3.3 主板(INTEl P965)";
        public override void SetupCpu() => computer.Cpu = "Intel 酷睿E4400 (2.0GHz/LGA 775/2M/800MHz)盒裝";
        public override void SetupMemory() => computer.Memory = "G.SKILl 芝奇F2-6400CL5D-2GBNQ DDR2 800 1G*2";
        public override void SetupHarddisk() => computer.Harddisk = "Hitachi日立SATAII 250G/7200轉/8M";
        public override void SetupVideocard() => computer.Videocard = "七彩虹GT-GD3 UP烈焰戰神H10 (GeForce 8600GT/256M/DDR3)支援HDMI";
    }
    class Computer
    {
        public string Videocard { get; set; }
        public string Cpu { get; set; }
        public string Mainboard { get; set; }
        public string Memory { get; set; }
        public string Harddisk { get; set; }
        public void ShowSystemInfo()
        {
            Console.WriteLine("==================SystemInfo==================");
            Console.WriteLine($"CPU:{Cpu}");
            Console.WriteLine($"MainBoard:{Mainboard}");
            Console.WriteLine($"Memory:{Memory}");
            Console.WriteLine($"VideoCard:{Videocard}");
            Console.WriteLine($"HardDisk:{Harddisk}");
        }
    }
}

程式碼執行結果

程式碼解析

ComputerFactory：Director（指導者），執行穩定構建流程，不知零件具體規格，只負責按序組裝。
ComputerBuilder：抽象建造者，規範產品組成介面（5 道工序）與回傳產品介面（此處省略抽象方法，產品皆為 Computer）。
OfficeComputerBuilder/GameComputerBuilder：具體建造者，實作各工序與回傳產品。
Computer：複雜產品，各工序服務於產品各部件。可抽象化使不同建造者產出完全不同產品。
客戶端：選擇具體 Builder → 讓 Factory 構建 → 驗收配置。用戶明確需求（辦公/遊戲），對組裝細節零認知。
Builder vs Abstract Factory：前者強調「組裝」有序序列，後者強調「創建一系列產品」。Builder 適用組裝電腦，Abstract Factory 適用提供筆記本/桌機/掌機產品線。