Notifications in wxWidgets?

Question

I'm working on a small application using C++/wxWidgets, where several parts of the GUI need to be updated based on e.g. received UDP datagrams. More specifically, a secondary thread tries to keep a list of available "clients" in the network (which may come and go away) and e.g. corresponding comboboxes in the UI need to be updated to reflect the changes.

The documentation mentions that for this kind of thing EVT_UPDATE_UI would be a good choice. As far as I can understand from the sparse documentation, this event is sent automatically by the system and provides some support for assisted UI change.

However, I'd feel more comfortable using a more direct approach, i.e. where e.g. a window object could register/subscribe to receive notifications (either events or callbacks) upon particular events and another part of the code is sending out these notifications when required. I could do this in C++ using my own code, however I guess if wxWidgets already supports something like that, I should make use of it. However I haven't found anything in that regards.

So, the question is: does wxWidgets support this kind of notification system (or similar alternatives) or would I be best served coding my own?

Answer 1

AFAIK there is nothing directly usable in wxWidgets, but doing it on your own seems easy.

What I would do:

• Create a wxEvtHandler-descendent class to hold the list of available "clients" in the network. Let this class have a wxCriticalSection, and use a wxCriticalSectionLocker for that in all methods that add or delete "clients".

• Create a worker thread class by inheriting wxThread to handle your UDP datagrams, using blocking calls. The thread should directly call methods of the client list object whenever a client has to be added or removed. In these methods update the list of clients, and ::wxPostEvent() an event to itself (this will execute the whole notification calls in the main GUI thread).

• Handle the event in the client list class, and notify all listeners that the list of clients has changed. The observer pattern seems to me a good fit. You could either call a method of all registered listeners directly, or send a wxCommandEvent to them.

Answer 2

Have you tried calling Update() on the widget(s) that change? Once you update the contents of the combo box, call Update(), and the contents should update.