Command

// Command pattern -- Real World example

using System; using System.Collections; namespace DoFactory.GangOfFour.Command.RealWorld {    // MainApp test application    class MainApp   {      static void Main()     {        // Create user and let her compute       User user = new User();       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.Read();     }   }    // "Command"    abstract class Command   {      public abstract void Execute();      public abstract void UnExecute();   }    // "ConcreteCommand"    class CalculatorCommand : Command   {      char @operator;      int operand;     Calculator calculator;      // Constructor      public CalculatorCommand(Calculator calculator,        char @operator, int operand)     {        this.calculator = calculator;        this.@operator = @operator;        this.operand = operand;     }      public char Operator     {        set{ @operator = value; }     }      public int Operand     {        set{ operand = value; }     }      public override void Execute()     {       calculator.Operation(@operator, operand);     }      public override void UnExecute()     {       calculator.Operation(Undo(@operator), operand);     }      // Private helper function      private char Undo( char @operator)     {        char undo;        switch(@operator)       {          case '+': undo = '-'; break;          case '-': undo = '+'; break;          case '*': undo = '/'; break;          case '/': undo = '*'; break;          default : undo = ' '; break;       }        return undo;     }   }    // "Receiver"    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);     }   }    // "Invoker"    class User   {      // Initializers      private Calculator calculator = new Calculator();      private ArrayList commands = new ArrayList();      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++] as Command;           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++;     }   } }