Command

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace Command{ class Program { static void Main(string[] args) { // 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); // Wait for user Console.ReadKey(); } } /// <summary> /// The 'Command' abstract class /// </summary> abstract class Command { public abstract void Execute(); public abstract void UnExecute(); } /// <summary> /// The 'ConcreteCommand' class /// </summary> class CalculatorCommand : Command { private char _operator; private int _operand; private Calculator _calculator; // Constructor 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 public override void Execute() { _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"); } } } /// <summary> /// The 'Receiver' class /// </summary> class Calculator { private int _curr = 0; public void Operation(char @operator, int operand) { switch (@operator) { 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); } } /// <summary> /// The 'Invoker' class /// </summary> class User { // Initializers private Calculator _calculator = new Calculator(); private List<Command> _commands = new List<Command>(); private 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++]; command.Execute(); } } } public void Undo(int levels) { Console.WriteLine("/n---- Undo {0} levels ", levels); // Perform undo operations for (int i = 0; i < levels; i++) { 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); command.Execute(); // Add command to undo list _commands.Add(command); _current++; } }}