c++ - 事件系统的类型安全实现

Question

我已经为我的游戏编写了一个事件系统。它工作正常但有一个很大的缺陷——它不是类型安全的，因此需要订阅的回调函数手动转换接收到的基本事件。现在，我正在尝试使用模板实现类型安全版本。我对这个话题总体上没问题，但显然不是专家。

首先，这里有一些代码演示了我想如何使用该事件:

定义派生事件

// Derived Events
class ClickEvent : public Event
{
public:
    float x;
    float y;
};

class RenderNodeCreatedEvent : public Event
{
public:
    unsigned long long int renderNodeId;
};

创建并使用它们(例如在主程序中用于测试目的)

// Create the on event functions
std::function<void(const ClickEvent &)> onClickFunction = [](const ClickEvent & event)
{
    std::cout << std::endl << "Mouse clicked at position: " << event.x << event.y;
};

std::function<void(const RenderNodeCreatedEvent &)> onRenderNodeCreatedFunction = [](const RenderNodeCreatedEvent & event)
{
    std::cout << std::endl << "Render node created with id: " << event.renderNodeId;
};

// Create the events
ClickEvent clickEvent;
clickEvent.x = 300.f;
clickEvent.y = 255.5f;

RenderNodeCreatedEvent renderNodeCreatedEvent;
renderNodeCreatedEvent.renderNodeId = 26234628374324;

// Create the event manager and subscribe the event functions
EventManager eventManager;
eventManager.Subscribe(onClickFunction);
eventManager.Subscribe(onRenderNodeCreatedFunction);

// Raise the events
eventManager.Raise(clickEvent);
eventManager.Raise(renderNodeCreatedEvent);

以下是我尝试为每个派生事件类生成 std::size_t 类型的唯一 ID:

class BaseEvent
{
public:
    typedef std::size_t ID;

    BaseEvent() = default;
    virtual ~BaseEvent() = default;

protected:
    static ID GetNextID()
    {
        static ID id = 0;
        return id++;
    }
};

class Event : public BaseEvent
{
public:
    Event() = default;
    virtual ~Event() = default;

    // Sets a unique id for the event the first time this function is called
    ID GetID()
    {
        static ID id = BaseEvent::GetNextID();
        return id;
    }
};

最后，这是我对可以提供上述功能的事件管理器的(糟糕的)尝试。我真的很难管理正确的转换和/或存储不同类型的回调函数。回调包装器不起作用 - 它只是我必须解决这个问题的一个基本想法，所以我将它包含在帖子中。

class EventManager
{
public:
    // Define the template callback type
    template <class DerivedEvent>
    using TCallback = std::function<void(const DerivedEvent &)>;

public:
    EventManager() = default;
    ~EventManager() = default;

    template<class DerivedEvent>
    void Subscribe(TCallback<DerivedEvent> callback)
    {
        // Get the index of the callback list this callback will be added to
        Event::ID id = DerivedEvent::GetID();

        // This won't work sinve TCallback is a different type than TCallback<Event>
        callbackListList[id].push_back(callback);
    }

    template <class DerivedEvent>
    void Raise(DerivedEvent event)
    {
        // Get the type of the event and therefore the index in the callbackListList
        Event::ID = DerivedEvent::GetID();

        /// How to cast the events back
        // Get the respective list of callback functions
        std::vector<TCallback<DerivedEvent>> /*&*/ callbackList;

        // Create a callback wrapper of with the type 'derived event' ?????
        CallbackWrapper<DerivedEvent> callbackWrapper(/*derived callback*/);
        // Call the callback wrapper using the base event ?????
    }

    template <typename DerivedEvent>
    class CallbackWrapper
    {
    public:
        CallbackWrapper(TCallback<DerivedEvent> callback) : callback(callback) {}

        void operator () (const Event & event)
        {
            callback(static_cast<const Event<DerivedEvent> &>(event).event);
        }

    private:
        TCallback<DerivedEvent> callback;
    };

private:
    std::vector<std::vector<TCallback<Event>>> callbackListList;
};

我知道这是很多代码，但我觉得这是演示我在说什么的最简单方法。

谢谢你的帮助，阿德里安

编辑: 必须将 Event 类声明为模板以获得派生类型的唯一 ID。

template <class DerivedEvent>
class Event : public BaseEvent

现在从 Event 继承时:

class ClickEvent : public Event<ClickEvent>
class RenderNodeCreatedEvent : public Event<RenderNodeCreatedEvent>

最后，EventManager 只能存储类型为 BaseEvent

的回调 vector 的 vector

private:
    std::vector<std::vector<TCallback<BaseEvent>>> callbackListList;

Answer 1

经过更长时间的研究，我发现这篇关于 ECS 事件/信使实现的帖子基本上解决了这个问题:

https://codereview.stackexchange.com/questions/79211/ecs-event-messaging-implementation