class1.cs

来自DoFactory的设计模式, 由于是本人根据已有代码创建,没有NETOptimized项

// 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++;
        }
    }
}