c++ - 类似于 C# (.NET?) 的事件系统

Question

在 C# 中（至少使用 .NET，但我认为它是通用的），您可以创建这样的事件：Understanding events and event handlers in C#。

C++ 有类似的机制吗？

PS：我从来不喜欢信号/插槽系统，所以请不要推荐它，因为我已经在使用它并且很想切换到其他东西。

Answer 1

C# 中的事件机制实际上只是观察者模式的正式语言实现版本。这种模式可以用任何语言实现，包括 C++。C++ 中有许多实现示例。

最大和最常见的实现可能是Boost.Signals和Boost.Signals2，尽管您明确提到不喜欢信号/插槽样式的实现。

Answer 2

Event.h 可以从下面的链接下载，它提供了一个用 C++ 实现的类似.NET 的事件：http: //www.codeproject.com/Tips/1069718/Sharp-Tools-A-NET-like-Event-in- Cplusplus

其用法示例：

#include "Event.h"  // This lib consists of only one file, just copy it and include it in your code.

// an example of an application-level component which perform part of the business logic
class Cashier
{
public:
  Sharp::Event<void> ShiftStarted;  // an event that pass no argument when raised
  Sharp::Event<int> MoneyPaid;  // will be raised whenever the cashier receives money

  void Start();  // called on startup, perform business logic and eventually calls ProcessPayment()

private:
  // somewhere along the logic of this class
  void ProcessPayment(int amount)
  {
    // after some processing
    MoneyPaid(amount);  // this how we raise the event
  }
};

// Another application-level component
class Accountant
{
public:
  void OnMoneyPaid(int& amount);
};

// The main class that decide on the events flow (who handles which events)
// it is also the owner of the application-level components
class Program
{
  // the utility level components(if any)
  //(commented)DataStore databaseConnection;

  // the application-level components
  Cashier cashier1;
  Accountant accountant1;
  //(commented)AttendanceManager attMan(&databaseConnection) // an example of injecting a utility object

public:
  Program()
  {
    // connect the events of the application-level components to their handlers
    cashier1.MoneyPaid += Sharp::EventHandler::Bind( &Accountant::OnMoneyPaid, &accountant1);
  }

  ~Program()
  {
    // it is recommended to always connect the event handlers in the constructor 
    // and disconnect in the destructor
    cashier1.MoneyPaid -= Sharp::EventHandler::Bind( &Accountant::OnMoneyPaid, &accountant1);
  }

  void Start()
  {
    // start business logic, maybe tell all cashiers to start their shift
    cashier1.Start();
  }
};

void main()
{
  Program theProgram;
  theProgram.Start();

  // as you can see the Cashier and the Accountant know nothing about each other
  // You can even remove the Accountant class without affecting the system
  // You can add new components (ex: AttendanceManager) without affecting the system
  // all you need to change is the part where you connect/disconnect the events
}

Answer 3

如果 boost 不是一个选项，我在这里用 c++ 实现了事件。语义几乎与 .NET 中的相同。这是一个紧凑的实现，但使用了相当先进的 C++ 功能：需要现代 C++11 编译器。