نوشته شده توسط
mohsen_csharp
ممکن است در مورد pattern command کمی توضیح دهید و از آن در برنامه خود چگونه استفاده کنم.
با استفاده از این الگو میتوان درخواستها و تراکنش ها رو در قالب یک آبجکت Encapsulate کرد.
// 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++;
}
}
}