23中设计模式——Command模式

一、描述

有时需要向对象发送请求，但是不知道 "被请求的操作" 或 "请求的接受者" 的任何信息。在面向过程的程序设计语言中，这类通信是通过回调函数来完成的：在某个地方登记这个函数，然后在后面调用它。在面向对象程序中，command(命令)与回调函数等价，它封装了回调函数。

Command模式(命令模式)是一种对象行为模式，它可以对发送者(sender)和接收者(receiver)完全解耦(decoupling)。（"发送者" 是请求操作的对象，"接收者" 是接收请求并执行某操作的对象。有了 "解耦"，发送者对接收者的接口一无所知。）这里，"请求"(request)这个术语指的是要被执行的命令。Command模式还让我们可以对 "何时" 以及 "如何" 完成请求进行改变。因此，Command模式为我们提供了灵活性和可扩展性。

二、结构图

三、代码

 

class Transaction{public:virtual ~Transaction(){}virtual void Execute() = 0;};class DepositUI{public:virtual ~DepositUI(){}virtual void RequestDepositAmount() = 0;};class DepositTransaction : public Transaction{public:DepositTransaction(DepositUI& ui) : itsDepositUI(ui){}~DepositTransaction(){}public:virtual void Execute(){itsDepositUI.RequestDepositAmount();}private:DepositUI& itsDepositUI;};class WithdrawalUI{public:virtual ~WithdrawalUI(){}virtual void RequestWithDrawalAmount() = 0;};class WithdrawalTransaction : public Transaction{public:WithdrawalTransaction(WithdrawalUI& ui) : itsWithdrawdrawalUI(ui){}~WithdrawalTransaction(){}public:virtual void Execute(){itsWithdrawdrawalUI.RequestWithDrawalAmount();}private:WithdrawalUI& itsWithdrawdrawalUI;};class TransferUI{public:virtual ~TransferUI(){}virtual void RequestTransferAmount() = 0;};class TransferTransaction : public Transaction{public:TransferTransaction(TransferUI& ui) : itsTransferUI(ui){}~TransferTransaction(){}public:virtual void Execute(){itsTransferUI.RequestTransferAmount();}private:TransferUI& itsTransferUI;};class UI : public DepositUI, public WithdrawalUI, public TransferUI{public:UI(){}~UI(){}public:virtual void RequestDepositAmount(){printf("RequestDepositAmount Request. \n");}virtual void RequestWithDrawalAmount(){printf("RequestWithDrawalAmount Request. \n");}virtual void RequestTransferAmount(){printf("RequestTransferAmount Request. \n");}};

Demo代码

static UI gui;void TransactionDemo(){Transaction* transaction1 = new DepositTransaction(gui);Transaction* transaction2 = new WithdrawalTransaction(gui);Transaction* transaction3 = new TransferTransaction(gui);transaction1->Execute();transaction2->Execute();transaction3->Execute();delete transaction1;delete transaction2;delete transaction3;}