{"id":113,"date":"2008-03-08T13:44:19","date_gmt":"2008-03-08T13:44:19","guid":{"rendered":""},"modified":"2008-03-08T13:44:19","modified_gmt":"2008-03-08T13:44:19","slug":"113","status":"publish","type":"post","link":"https:\/\/www.poloo.org\/?p=113","title":{"rendered":"\u547d\u4ee4\u6a21\u5f0f(Command Pattern)"},"content":{"rendered":"

\u4e00\u3001 \u547d\u4ee4\uff08Command\uff09\u6a21\u5f0f
\u547d\u4ee4\uff08Command\uff09\u6a21\u5f0f\u5c5e\u4e8e\u5bf9\u8c61\u7684\u884c\u4e3a\u6a21\u5f0f\u3010GOF95\u3011\u3002\u547d\u4ee4\u6a21\u5f0f\u53c8\u79f0\u4e3a\u884c\u52a8\uff08Action\uff09\u6a21\u5f0f\u6216\u4ea4\u6613\uff08Transaction\uff09\u6a21\u5f0f\u3002\u547d\u4ee4\u6a21\u5f0f\u628a\u4e00\u4e2a\u8bf7\u6c42\u6216\u8005\u64cd\u4f5c\u5c01\u88c5\u5230\u4e00\u4e2a\u5bf9\u8c61\u4e2d\u3002\u547d\u4ee4\u6a21\u5f0f\u5141\u8bb8\u7cfb\u7edf\u4f7f\u7528\u4e0d\u540c\u7684\u8bf7\u6c42\u628a\u5ba2\u6237\u7aef\u53c2\u6570\u5316\uff0c\u5bf9\u8bf7\u6c42\u6392\u961f\u6216\u8005\u8bb0\u5f55\u8bf7\u6c42\u65e5\u5fd7\uff0c\u53ef\u4ee5\u63d0\u4f9b\u547d\u4ee4\u7684\u64a4\u9500\u548c\u6062\u590d\u529f\u80fd\u3002<\/p>\n

\u547d\u4ee4\u6a21\u5f0f\u662f\u5bf9\u547d\u4ee4\u7684\u5c01\u88c5\u3002\u547d\u4ee4\u6a21\u5f0f\u628a\u53d1\u51fa\u547d\u4ee4\u7684\u8d23\u4efb\u548c\u6267\u884c\u547d\u4ee4\u7684\u8d23\u4efb\u5206\u5272\u5f00\uff0c\u59d4\u6d3e\u7ed9\u4e0d\u540c\u7684\u5bf9\u8c61\u3002<\/p>\n

\u6bcf\u4e00\u4e2a\u547d\u4ee4\u90fd\u662f\u4e00\u4e2a\u64cd\u4f5c\uff1a\u8bf7\u6c42\u7684\u4e00\u65b9\u53d1\u51fa\u8bf7\u6c42\u8981\u6c42\u6267\u884c\u4e00\u4e2a\u64cd\u4f5c\uff1b\u63a5\u6536\u7684\u4e00\u65b9\u6536\u5230\u8bf7\u6c42\uff0c\u5e76\u6267\u884c\u64cd\u4f5c\u3002\u547d\u4ee4\u6a21\u5f0f\u5141\u8bb8\u8bf7\u6c42\u7684\u4e00\u65b9\u548c\u63a5\u6536\u7684\u4e00\u65b9\u72ec\u7acb\u5f00\u6765\uff0c\u4f7f\u5f97\u8bf7\u6c42\u7684\u4e00\u65b9\u4e0d\u5fc5\u77e5\u9053\u63a5\u6536\u8bf7\u6c42\u7684\u4e00\u65b9\u7684\u63a5\u53e3\uff0c\u66f4\u4e0d\u5fc5\u77e5\u9053\u8bf7\u6c42\u662f\u600e\u4e48\u88ab\u63a5\u6536\uff0c\u4ee5\u53ca\u64cd\u4f5c\u662f\u5426\u88ab\u6267\u884c\u3001\u4f55\u65f6\u88ab\u6267\u884c\uff0c\u4ee5\u53ca\u662f\u600e\u4e48\u88ab\u6267\u884c\u7684\u3002<\/p>\n

\u4e8c\u3001 \u547d\u4ee4\u6a21\u5f0f\u7684\u7ed3\u6784
\u547d\u4ee4\u6a21\u5f0f\u7684\u7c7b\u56fe\u5982\u4e0b\uff1a

\u547d\u4ee4\u6a21\u5f0f\u6d89\u53ca\u5230\u4e94\u4e2a\u89d2\u8272\uff0c\u5b83\u4eec\u5206\u522b\u662f\uff1a<\/p>\n

\u5ba2\u6237\uff08Client\uff09\u89d2\u8272\uff1a\u521b\u5efa\u4e86\u4e00\u4e2a\u5177\u4f53\u547d\u4ee4(ConcreteCommand)\u5bf9\u8c61\u5e76\u786e\u5b9a\u5176\u63a5\u6536\u8005\u3002
\u547d\u4ee4\uff08Command\uff09\u89d2\u8272\uff1a\u58f0\u660e\u4e86\u4e00\u4e2a\u7ed9\u6240\u6709\u5177\u4f53\u547d\u4ee4\u7c7b\u7684\u62bd\u8c61\u63a5\u53e3\u3002\u8fd9\u662f\u4e00\u4e2a\u62bd\u8c61\u89d2\u8272\u3002
\u5177\u4f53\u547d\u4ee4\uff08ConcreteCommand\uff09\u89d2\u8272\uff1a\u5b9a\u4e49\u4e00\u4e2a\u63a5\u53d7\u8005\u548c\u884c\u4e3a\u4e4b\u95f4\u7684\u5f31\u8026\u5408\uff1b\u5b9e\u73b0Execute()\u65b9\u6cd5\uff0c\u8d1f\u8d23\u8c03\u7528\u63a5\u6536\u8003\u7684\u76f8\u5e94\u64cd\u4f5c\u3002Execute()\u65b9\u6cd5\u901a\u5e38\u53eb\u505a\u6267\u65b9\u6cd5\u3002
\u8bf7\u6c42\u8005\uff08Invoker\uff09\u89d2\u8272\uff1a\u8d1f\u8d23\u8c03\u7528\u547d\u4ee4\u5bf9\u8c61\u6267\u884c\u8bf7\u6c42\uff0c\u76f8\u5173\u7684\u65b9\u6cd5\u53eb\u505a\u884c\u52a8\u65b9\u6cd5\u3002
\u63a5\u6536\u8005\uff08Receiver\uff09\u89d2\u8272\uff1a\u8d1f\u8d23\u5177\u4f53\u5b9e\u65bd\u548c\u6267\u884c\u4e00\u4e2a\u8bf7\u6c42\u3002\u4efb\u4f55\u4e00\u4e2a\u7c7b\u90fd\u53ef\u4ee5\u6210\u4e3a\u63a5\u6536\u8005\uff0c\u5b9e\u65bd\u548c\u6267\u884c\u8bf7\u6c42\u7684\u65b9\u6cd5\u53eb\u505a\u884c\u52a8\u65b9\u6cd5\u3002 <\/p>\n

\u4e09\u3001 \u547d\u4ee4\u6a21\u5f0f\u7684\u793a\u610f\u6027\u6e90\u4ee3\u7801<\/p>\n

\/\/ Command pattern -- Structural example  
using System; <\/p>\n

\/\/ \"Command\"
abstract class Command
{
  \/\/ Fields
  protected Receiver receiver; <\/p>\n

  \/\/ Constructors
  public Command( Receiver receiver )
  {
    this.receiver = receiver;
  } <\/p>\n

  \/\/ Methods
  abstract public void Execute();
} <\/p>\n

\/\/ \"ConcreteCommand\"
class ConcreteCommand : Command
{
  \/\/ Constructors
  public ConcreteCommand( Receiver receiver ) :
    base ( receiver ) {} <\/p>\n

  \/\/ Methods
  public override void Execute()
  {
    receiver.Action();
  }
} <\/p>\n

\/\/ \"Receiver\"
class Receiver
{
  \/\/ Methods
  public void Action()
  {
    Console.WriteLine(\"Called Receiver.Action()\");
  }
} <\/p>\n

\/\/ \"Invoker\"
class Invoker
{
  \/\/ Fields
  private Command command; <\/p>\n

  \/\/ Methods
  public void SetCommand( Command command )
  {
    this.command = command;
  } <\/p>\n

  public void ExecuteCommand()
  {
    command.Execute();
  }
} <\/p>\n

\/**\/\/\/\/ <summary>
\/\/\/  Client test
\/\/\/ <\/summary>
public class Client
{
  public static void Main( string[] args )
  {
    \/\/ Create receiver, command, and invoker
    Receiver r = new Receiver();
    Command c = new ConcreteCommand( r );
    Invoker i = new Invoker(); <\/p>\n

    \/\/ Set and execute command
    i.SetCommand(c);
    i.ExecuteCommand();
  }
}
<\/code><\/p>\n

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\u8fd9\u4e2a\u6a21\u62df\u7cfb\u7edf\u7684\u8bbe\u8ba1\u5982\u4e0b\uff1a

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\u5176\u6b21\u662f\u5426\u652f\u6301undo\u548credo\u3002\u5982\u679c\u4e00\u4e2a\u547d\u4ee4\u7c7b\u63d0\u4f9b\u4e00\u4e2a\u65b9\u6cd5\uff0c\u6bd4\u5982\u53ebunExecute()\uff0c\u4ee5\u6062\u590d\u5176\u64cd\u4f5c\u7684\u6548\u679c\uff0c\u90a3\u4e48\u547d\u4ee4\u7c7b\u5c31\u53ef\u4ee5\u652f\u6301undo\u548credo\u3002\u5177\u4f53\u547d\u4ee4\u7c7b\u9700\u8981\u5b58\u50a8\u72b6\u6001\u4fe1\u606f\uff0c\u5305\u62ec\uff1a<\/p>\n

1. \u63a5\u6536\u8005\u5bf9\u8c61\u5b9e\u9645\u4e0a\u5b9e\u65bd\u8bf7\u6c42\u6240\u4ee3\u8868\u7684\u64cd\u4f5c\uff1b
2. \u5bf9\u63a5\u6536\u8005\u5bf9\u8c61\u6240\u4f5c\u7684\u64cd\u4f5c\u6240\u9700\u8981\u7684\u53c2\u6570\uff1b
3. \u63a5\u6536\u8005\u7c7b\u7684\u6700\u521d\u7684\u72b6\u6001\u3002\u63a5\u6536\u8005\u5fc5\u987b\u63d0\u4f9b\u9002\u5f53\u7684\u65b9\u6cd5\uff0c\u4f7f\u547d\u4ee4\u7c7b\u53ef\u4ee5\u901a\u8fc7\u8c03\u7528\u8fd9\u4e2a\u65b9\u6cd5\uff0c\u4ee5\u4fbf\u63a5\u6536\u8005\u7c7b\u6062\u590d\u539f\u6709\u72b6\u6001\u3002 <\/p>\n

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\u4e0b\u9762\u7684\u4ee3\u7801\u4f7f\u7528\u547d\u4ee4\u6a21\u5f0f\u6f14\u793a\u4e86\u4e00\u4e2a\u7b80\u5355\u7684\u8ba1\u7b97\u5668\uff0c\u5e76\u5141\u8bb8\u6267\u884cundo\u4e0eredo\u3002\u6ce8\u610f\uff1a”operator”\u5728C#\u4e2d\u662f\u5173\u952e\u8bcd\uff0c\u6240\u4ee5\u5728\u524d\u9762\u6dfb\u52a0\u4e00\u4e2a”@”\u5c06\u5176\u53d8\u4e3a\u6807\u8bc6\u7b26\u3002<\/p>\n

\/\/ Command pattern -- Real World example  
using System;
using System.Collections; <\/p>\n

\/\/ \"Command\"
abstract class Command
{
  \/\/ Methods
  abstract public void Execute();
  abstract public void UnExecute();
} <\/p>\n

\/\/ \"ConcreteCommand\"
class CalculatorCommand : Command
{
  \/\/ Fields
  char @operator;
  int operand;
  Calculator calculator; <\/p>\n

  \/\/ Constructor
  public CalculatorCommand( Calculator calculator,
    char @operator, int operand )
  {
    this.calculator = calculator;
    this.@operator = @operator;
    this.operand = operand;
  } <\/p>\n

  \/\/ Properties
  public char Operator
  {
    set{ @operator = value; }
  } <\/p>\n

  public int Operand
  {
    set{ operand = value; }
  } <\/p>\n

  \/\/ Methods
  override public void Execute()
  {
    calculator.Operation( @operator, operand );
  }
  
  override public void UnExecute()
  {
    calculator.Operation( Undo( @operator ), operand );
  } <\/p>\n

  \/\/ Private helper function
  private char Undo( char @operator )
  {
    char undo = ' ';
    switch( @operator )
    {
      case '+': undo = '-'; break;
      case '-': undo = '+'; break;
      case '*': undo = '\/'; break;
      case '\/': undo = '*'; break;
    }
    return undo;
  }
} <\/p>\n

\/\/ \"Receiver\"
class Calculator
{
  \/\/ Fields
  private int total = 0; <\/p>\n

  \/\/ Methods
  public void Operation( char @operator, int operand )
  {
    switch( @operator )
    {
      case '+': total += operand; break;
      case '-': total -= operand; break;
      case '*': total *= operand; break;
      case '\/': total \/= operand; break;
    }
    Console.WriteLine( \"Total = {0} (following {1} {2})\",
      total, @operator, operand );
  }
} <\/p>\n

\/\/ \"Invoker\"
class User
{
  \/\/ Fields
  private Calculator calculator = new Calculator();
  private ArrayList commands = new ArrayList();
  private int current = 0; <\/p>\n

  \/\/ Methods
  public void Redo( int levels )
  {
    Console.WriteLine( \"---- Redo {0} levels \", levels );
    \/\/ Perform redo operations
    for( int i = 0; i < levels; i++ )
      if( current < commands.Count - 1 )
        ((Command)commands[ current++ ]).Execute();
  } <\/p>\n

  public void Undo( int levels )
  {
    Console.WriteLine( \"---- Undo {0} levels \", levels );
    \/\/ Perform undo operations
    for( int i = 0; i < levels; i++ )
      if( current > 0 )
        ((Command)commands[ --current ]).UnExecute();
  } <\/p>\n

  public void Compute( char @operator, int operand )
  {
    \/\/ Create command operation and execute it
    Command command = new CalculatorCommand(
      calculator, @operator, operand );
    command.Execute(); <\/p>\n

    \/\/ Add command to undo list
    commands.Add( command );
    current++;
  }
} <\/p>\n

\/**\/\/\/\/ <summary>
\/\/\/ CommandApp test
\/\/\/ <\/summary>
public class Client
{
  public static void Main( string[] args )
  {
    \/\/ Create user and let her compute
    User user = new User(); <\/p>\n

    user.Compute( '+', 100 );
    user.Compute( '-', 50 );
    user.Compute( '*', 10 );
    user.Compute( '\/', 2 ); <\/p>\n

    \/\/ Undo and then redo some commands
    user.Undo( 4 );
    user.Redo( 3 );
  }
}
<\/code><\/p>\n

\u4e03\u3001 \u5728\u4ec0\u4e48\u60c5\u51b5\u4e0b\u5e94\u5f53\u4f7f\u7528\u547d\u4ee4\u6a21\u5f0f
\u5728\u4e0b\u9762\u7684\u60c5\u51b5\u4e0b\u5e94\u5f53\u8003\u8651\u4f7f\u7528\u547d\u4ee4\u6a21\u5f0f\uff1a<\/p>\n

1\u3001\u4f7f\u7528\u547d\u4ee4\u6a21\u5f0f\u4f5c\u4e3a”CallBack”\u5728\u9762\u5411\u5bf9\u8c61\u7cfb\u7edf\u4e2d\u7684\u66ff\u4ee3\u3002”CallBack”\u8bb2\u7684\u4fbf\u662f\u5148\u5c06\u4e00\u4e2a\u51fd\u6570\u767b\u8bb0\u4e0a\uff0c\u7136\u540e\u5728\u4ee5\u540e\u8c03\u7528\u6b64\u51fd\u6570\u3002<\/p>\n

2\u3001\u9700\u8981\u5728\u4e0d\u540c\u7684\u65f6\u95f4\u6307\u5b9a\u8bf7\u6c42\u3001\u5c06\u8bf7\u6c42\u6392\u961f\u3002\u4e00\u4e2a\u547d\u4ee4\u5bf9\u8c61\u548c\u539f\u5148\u7684\u8bf7\u6c42\u53d1\u51fa\u8005\u53ef\u4ee5\u6709\u4e0d\u540c\u7684\u751f\u547d\u671f\u3002\u6362\u8a00\u4e4b\uff0c\u539f\u5148\u7684\u8bf7\u6c42\u53d1\u51fa\u8005\u53ef\u80fd\u5df2\u7ecf\u4e0d\u5728\u4e86\uff0c\u800c\u547d\u4ee4\u5bf9\u8c61\u672c\u8eab\u4ecd\u7136\u662f\u6d3b\u52a8\u7684\u3002\u8fd9\u65f6\u547d\u4ee4\u7684\u63a5\u6536\u8005\u53ef\u4ee5\u662f\u5728\u672c\u5730\uff0c\u4e5f\u53ef\u4ee5\u5728\u7f51\u7edc\u7684\u53e6\u5916\u4e00\u4e2a\u5730\u5740\u3002\u547d\u4ee4\u5bf9\u8c61\u53ef\u4ee5\u5728\u4e32\u5f62\u5316\u4e4b\u540e\u4f20\u9001\u5230\u53e6\u5916\u4e00\u53f0\u673a\u5668\u4e0a\u53bb\u3002<\/p>\n

3\u3001\u7cfb\u7edf\u9700\u8981\u652f\u6301\u547d\u4ee4\u7684\u64a4\u6d88(undo)\u3002\u547d\u4ee4\u5bf9\u8c61\u53ef\u4ee5\u628a\u72b6\u6001\u5b58\u50a8\u8d77\u6765\uff0c\u7b49\u5230\u5ba2\u6237\u7aef\u9700\u8981\u64a4\u9500\u547d\u4ee4\u6240\u4ea7\u751f\u7684\u6548\u679c\u65f6\uff0c\u53ef\u4ee5\u8c03\u7528undo()\u65b9\u6cd5\uff0c\u628a\u547d\u4ee4\u6240\u4ea7\u751f\u7684\u6548\u679c\u64a4\u9500\u6389\u3002\u547d\u4ee4\u5bf9\u8c61\u8fd8\u53ef\u4ee5\u63d0\u4f9bredo()\u65b9\u6cd5\uff0c\u4ee5\u4f9b\u5ba2\u6237\u7aef\u5728\u9700\u8981\u65f6\uff0c\u518d\u91cd\u65b0\u5b9e\u65bd\u547d\u4ee4\u6548\u679c\u3002<\/p>\n

4\u3001\u5982\u679c\u4e00\u4e2a\u7cfb\u7edf\u8981\u5c06\u7cfb\u7edf\u4e2d\u6240\u6709\u7684\u6570\u636e\u66f4\u65b0\u5230\u65e5\u5fd7\u91cc\uff0c\u4ee5\u4fbf\u5728\u7cfb\u7edf\u5d29\u6e83\u65f6\uff0c\u53ef\u4ee5\u6839\u636e\u65e5\u5fd7\u91cc\u8bfb\u56de\u6240\u6709\u7684\u6570\u636e\u66f4\u65b0\u547d\u4ee4\uff0c\u91cd\u65b0\u8c03\u7528Execute()\u65b9\u6cd5\u4e00\u6761\u4e00\u6761\u6267\u884c\u8fd9\u4e9b\u547d\u4ee4\uff0c\u4ece\u800c\u6062\u590d\u7cfb\u7edf\u5728\u5d29\u6e83\u524d\u6240\u505a\u7684\u6570\u636e\u66f4\u65b0\u3002<\/p>\n

5\u3001\u4e00\u4e2a\u7cfb\u7edf\u9700\u8981\u652f\u6301\u4ea4\u6613(Transaction)\u3002\u4e00\u4e2a\u4ea4\u6613\u7ed3\u6784\u5c01\u88c5\u4e86\u4e00\u7ec4\u6570\u636e\u66f4\u65b0\u547d\u4ee4\u3002\u4f7f\u7528\u547d\u4ee4\u6a21\u5f0f\u6765\u5b9e\u73b0\u4ea4\u6613\u7ed3\u6784\u53ef\u4ee5\u4f7f\u7cfb\u7edf\u589e\u52a0\u65b0\u7684\u4ea4\u6613\u7c7b\u578b\u3002<\/p>\n

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\u547d\u4ee4\u6a21\u5f0f\u7684\u7f3a\u70b9\u5982\u4e0b\uff1a<\/p>\n

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