Re: [Boost-users] boost::bind and Motif

3 May 2012


      On Thursday, May 03, 2012 4:56 AM, Sven Bauhan wrote:
...
...
No, you don't have to make a signleton. The function XtAppAddTimeOut 
accepts "XtPointer client_data" argument, where you can pass "this".
Then you get it back in the callback function, and type-cast it to
its 
original type.
Ok this is another solution. But I don't like such pointer casts.
I have done it  the following way:
class AnimationController {
private:
     static boost::optional cInstance;
public:
     static AnimationController& instance() {
         return cInstance.get();
     }
     AnimationController() {
         cInstance = *this;
     }
     static void timerCB() {
         instance().animate();
     }
private:
     void animate();
};
Just as praise for boost::optional :-)
Sven
The implementation that comes to my mind involves the following helper
class or something similar (warning: untested):

//A generic wrapper for XtAppAddTimeOut
class AppTimeout
{
public:
	typedef boost::function  CallbackType;

	//Constructor registers the app_context and callback, but
doesn't start the timer.
	AppTimeout (XtAppContext app_context, CallbackType callback):
app_context (app_context), callback (callback), interval_id (0) {}

	~AppTimeout()
	{
		Cancel();  //Because the timer would cause undefined
behavior if it triggers after the destructor
	}

	void Schedule (unsigned long interval)
	{
		assert (!interval_id);  //This class only supports one
timeout per instance
		interval_id = XtAppAddTimeOut (app_context, interval,
&interval_callback, this);		
	}

	void Cancel()
	{
		if (interval_id)  //I won't consider redundant calls to
Cancel an error; just no effect
		{
			XtRemoveTimeOut (interval_id);
			interval_id = 0;
		}
	}

	bool Is_pending() const {return interval_id != 0;}

private:
	XtAppContext app_context;
	CallbackType callback;
	XtIntervalId interval_id;

	static void Internal_callback (XtPointer self, XtIntervalId*)
	{
		reinterpret_cast  (self)->callback();

		//According to
http://www.xfree86.org/current/XtAppAddTimeOut.3.html
		//a triggered timeout is automatically removed, so clear
its id.
		reinterpret_cast  (self)->interval_id = 0;
	}
};

Re: [Boost-users] boost::bind and Motif

Andrew Holden