2022行為型模式C#指令模式（Command Pattern）

Command 設計模式将請求封裝為對象，進而允許您使用不同的請求、隊列或日志請求參數化用戶端，并支援可撤消的操作。

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C# 中的結構代碼

#

此結構代碼示範了 Command 模式，該模式将請求存儲為允許用戶端執行或播放請求的對象。

• using System;
• namespace Command.Structural
• {
• /// <summary>
• /// Command Design Pattern
• /// </summary>
• public class Program
• public static void Main(string[] args)
• // Create receiver, command, and invoker
• Receiver receiver = new Receiver();
• Command command = new ConcreteCommand(receiver);
• Invoker invoker = new Invoker();
• // Set and execute command
• invoker.SetCommand(command);
• invoker.ExecuteCommand();
• // Wait for user
• Console.ReadKey();
• }
• /// The 'Command' abstract class
• public abstract class Command
• protected Receiver receiver;
• // Constructor
• public Command(Receiver receiver)
• this.receiver = receiver;
• public abstract void Execute();
• /// The 'ConcreteCommand' class
• public class ConcreteCommand : Command
• public ConcreteCommand(Receiver receiver) :
• base(receiver)
• public override void Execute()
• receiver.Action();
• /// The 'Receiver' class
• public class Receiver
• public void Action()
• Console.WriteLine("Called Receiver.Action()");
• /// The 'Invoker' class
• public class Invoker
• Command command;
• public void SetCommand(Command command)
• this.command = command;
• public void ExecuteCommand()
• command.Execute();

C# 中的實際代碼

此實際代碼示範了在簡單電腦中使用的指令模式，該電腦具有無限數量的撤消和重做。請注意，在 C# 中，單詞"operator"是一個關鍵字。在字首為字首"@"允許将其用作辨別符。

• using System.Collections.Generic;
• namespace Command.RealWorld
• // Create user and let her compute
• User user = new User();
• // User presses calculator buttons
• user.Compute('+', 100);
• user.Compute('-', 50);
• user.Compute('*', 10);
• user.Compute('/', 2);
• // Undo 4 commands
• user.Undo(4);
• // Redo 3 commands
• user.Redo(3);
• public abstract void UnExecute();
• public class CalculatorCommand : Command
• char @operator;
• int operand;
• Calculator calculator;
• public CalculatorCommand(Calculator calculator,
• char @operator, int operand)
• this.calculator = calculator;
• this.@operator = @operator;
• this.operand = operand;
• // Gets operator
• public char Operator
• set { @operator = value; }
• // Get operand
• public int Operand
• set { operand = value; }
• // Execute new command
• calculator.Operation(@operator, operand);
• // Unexecute last command
• public override void UnExecute()
• calculator.Operation(Undo(@operator), operand);
• // Returns opposite operator for given operator
• private char Undo(char @operator)
• switch (@operator)
• case '+': return '-';
• case '-': return '+';
• case '*': return '/';
• case '/': return '*';
• default:
• throw new
• ArgumentException("@operator");
• public class Calculator
• int curr = 0;
• public void Operation(char @operator, int operand)
• case '+': curr += operand; break;
• case '-': curr -= operand; break;
• case '*': curr *= operand; break;
• case '/': curr /= operand; break;
• Console.WriteLine(
• "Current value = {0,3} (following {1} {2})",
• curr, @operator, operand);
• public class User
• // Initializers
• Calculator calculator = new Calculator();
• List<Command> commands = new List<Command>();
• int current = 0;
• public void Redo(int levels)
• Console.WriteLine("\n---- Redo {0} levels ", levels);
• // Perform redo operations
• for (int i = 0; i < levels; i++)
• if (current < commands.Count - 1)
• Command command = commands[current++];
• public void Undo(int levels)
• Console.WriteLine("\n---- Undo {0} levels ", levels);
• // Perform undo operations
• if (current > 0)
• Command command = commands[--current] as Command;
• command.UnExecute();
• public void Compute(char @operator, int operand)
• // Create command operation and execute it
• Command command = new CalculatorCommand(calculator, @operator, operand);
• // Add command to undo list
• commands.Add(command);
• current++;