1.2设计模式在Unity中应用—Behavioral Pattern— Command Pattern 命令模式

Command Pattern 命令模式

Definition

Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.

命令模式将“请求”封装成对象，以便使用不同的请求、队列或者日志来参数化其他对象，同时支持可撤消的操作。

Participants

The classes and objects participating in this pattern are:

Command

• declares an interface for executing an operation

ConcreteCommand

• defines a binding between a Receiver object and an action
• implements Execute by invoking the corresponding operation(s) on Receiver

Client

• creates a ConcreteCommand object and sets its receiver

Invoker

• asks the command to carry out the request

Receiver

• knows how to perform the operations associated with carrying out the request.

责任链模式代码结构

//-------------------------------------------------------------------------------------
//  CommandStructure.cs
//-------------------------------------------------------------------------------------

using UnityEngine;
using System.Collections;

namespace CommandStructure
{
    public class CommandStructure : MonoBehaviour
    {
        void Start ( )
        {
            // Create receiver, command, and invoker
            Receiver receiver = new Receiver();
            Command command = new ConcreteCommand(receiver);
            Invoker invoker = new Invoker();

            // Set and execute command
            invoker.SetCommand(command);
            invoker.ExecuteCommand();
        }
    }

    /// <summary>
    /// The 'Command' abstract class
    /// </summary>
    abstract class Command
    {
        protected Receiver receiver;

        // Constructor
        public Command(Receiver receiver)
        {
            this.receiver = receiver;
        }

        public abstract void Execute();
    }

    /// <summary>
    /// The 'ConcreteCommand' class
    /// </summary>
    class ConcreteCommand : Command
    {
        // Constructor
        public ConcreteCommand(Receiver receiver) :
          base(receiver)
        {
        }

        public override void Execute()
        {
            receiver.Action();
        }
    }

    /// <summary>
    /// The 'Receiver' class
    /// </summary>
    class Receiver
    {
        public void Action()
        {
          Debug.Log("Called Receiver.Action()");
        }
    }

    /// <summary>
    /// The 'Invoker' class
    /// </summary>
    class Invoker
    {
        private Command _command;

        public void SetCommand(Command command)
        {
            this._command = command;
        }

        public void ExecuteCommand()
        {
            _command.Execute();
        }
    }

}

案例1：加减乘除计算器，可以执行撤销 重复 命令，

//-------------------------------------------------------------------------------------
//  CommandExample1.cs
//-------------------------------------------------------------------------------------

//This real-world code demonstrates the Command pattern used in a simple calculator with unlimited number of undo's and redo's.


using System;
using UnityEngine;
using System.Collections.Generic;

namespace CommandExample1
{
    public class CommandExample1 : MonoBehaviour
    {
        void Start ( )
        {
            // 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);
        }
    }

    /// <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 operatorSymbol, int operand)
        {
            this._calculator = calculator;
            this._operator = operatorSymbol;
            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 operatorSymbol)
        {
            switch (operatorSymbol)
            {
                case '+': return '-';
                case '-': return '+';
                case '*': return '/';
                case '/': return '*';
                default:
                    throw new
            ArgumentException("UnKnowOperatorSymbol");
            }
        }
    }

    /// <summary>
    /// The 'Receiver' class
    /// </summary>
    class Calculator
    {
        private int _curr = 0;

        public void Operation(char operatorSymbol, int operand)
        {
            switch (operatorSymbol)
            {
                case '+': _curr += operand; break;
                case '-': _curr -= operand; break;
                case '*': _curr *= operand; break;
                case '/': _curr /= operand; break;
            }
            Debug.Log("Current value = " + _curr+ " ( following "+ operatorSymbol+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)
        {
            Debug.Log("\n---- Redo " + levels + " levels");
            for (int i = 0; i < levels; i++)
            {
                if (_current < _commands.Count - 1)
                {
                    Command command = _commands[_current++];
                    command.Execute();
                }
            }
        }

        public void Undo(int levels)
        {
            Debug.Log("\n---- Undo "+ 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 operatorSymbol, int operand)
        {
            // Create command operation and execute it
            Command command = new CalculatorCommand(
              _calculator, operatorSymbol, operand);
            command.Execute();

            // Add command to undo list
            _commands.Add(command);
            _current++;
        }
    }
}