Limegarden.net Personal site of Wouter Lindenhof

Events in C++

This week I have decided to do some little work on Nova as I would like to use it for a game. But I’m currently missing a GUI. Since writing a GUI is often a pain while a nice GUI is its weight worth in gold it was worth to invest some time in it.
One of the very first things I have decided on is that I want a good and proper event management system. I like how it is done in C#

myButton.Click += new EventHandler(this.myButton_Click);

However something equally nice doesn't exist in plain C++, so I have decided to write one.

struct GuiEvent
{
	bool cancel;
	GuiEvent() : cancel(false) {}
};

class Button
{
public:
	Event<GuiEvent> OnDown;
	Event<GuiEvent> OnUp;

	void FireClickEvent()
	{
		size_t cycle = 0; GuiEvent e;
		while(OnDown.Fire(cycle, e)) {
			if(e.cancel == true) return;
		}
		e = GuiEvent(); cycle = 0;
		while(OnUp.Fire(cycle, e));
	}
};

class Application : public BaseEvent::Receiver<Application>
{
	Button m_StartButton;
public:
	Application()
	{
		RegisterEvent<GuiEvent>(m_StartButton.OnDown, &Application::StartDown);
		RegisterEvent<GuiEvent>(m_StartButton.OnUp,	&Application::StartUp);
		m_StartButton.FireClickEvent();
	}

	void StartUp(GuiEvent& eventParam)
	{
		std::cout << "The start button was released" << "\n";
	}
	void StartDown(GuiEvent& eventParam)
	{
		// If you set event param to true the release will never be called
		//eventParam.cancel = true;
		std::cout << "The start button is pressed down" << "\n";
	}
};

int main(int argc, const char* argv[])
{
	Application myApp;
	return 0;
}

The above is rather primitive as I have written it quickly, but it looks nice and is code that is easy to understand. For the full source click here (C++ example of events)