WxWidget ID issue

Question

The short: How to make sure that "statically" declared IDs for events and/or widgets don't clash across a medium to larger size project ?

...and the long:

One way of dealing with IDs in WxWidgets is to declare them by means of enumerations per compilation-unit, i.e. in the widget's source-file. However, when the IDs are used in WxWidgets' event-handling, they should or must be globally unique. Some don't need to be globally unique, but I think it's safer, if they all are, otherwise there's potential for runtime-"clashes", that don't trigger any warning - the event is simply handled by another widget. Unfortunately, I came across this issue a couple of times (inherited code-base) - they are hard to track down and rather annoying, unless I'm missing something. Anyway, I want to sort this out, once and for all :-)

I know, that WxWidgets also supports dynamic binding, and we/I use it in some places. However, changing the code for all the "statically" declared IDs would be way too much effort. So essentially what I have are many separate source-files (>60) where there are enumerations starting at wxID_HIGHEST with some (seemingly) arbitrary offset. I do think that the offset is arbitrary, likely to have been added to fix single cases of the above ID-clash problem. Anyway, putting all enumerations into a single file/enumeration seems a bit ugly, because it would be an incredibly long list.

So here is what I've been thinking: I maintain MIN/MAX-IDs for the different widgets in a single header-file using a single enumeration, and provide two macros that BEGIN and END a given ID-enumeration. The END-macro should also check that the declared MAX-ID is not exceeded. Does that sound sensible ? What are common ways of addressing the ID-clash issue ?

My intended solution looks something like the following. I plan to add a function that deals with IDs for dynamic binding. I know that WxWidgets provides related functionality with ID-reference-counting, however, I thought just while I'm at it... It is intended to be as platform-independent as possible.

#include <wx/defs.h>
#define NUM_OF_DYNAMIC_AUTO_IDS 500

namespace WxWidgetIdHelper {

  enum WxWidgetIDsEnum {
    MIN_DYNAMIC_AUTO_ID = wxID_HIGHEST + 1,
    MAX_DYNAMIC_AUTO_ID = MIN_DYNAMIC_AUTO_ID + NUM_OF_DYNAMIC_AUTO_IDS,
    STATIC_ID_OFFSET = MAX_DYNAMIC_AUTO_ID + 1,

    Widget1_MIN_ID = STATIC_ID_OFFSET + 1,
    Widget1_MAX_ID = Widget1_MIN_ID + 20,

    Widget2_MIN_ID = Widget1_MAX_ID + 1,
    Widget2_MAX_ID = Widget2_MIN_ID + 20,
    ...
  };

  template<bool> struct MaxIdCheck;
  template<> struct MaxIdCheck<false> {};
}

#define BEGIN_WXWIDGET_ID_ENUM(CLASSNAME) \
  enum CLASSNAME##_##WXWIDGET_IDs { \
    CLASSNAME##_##MIN_ID = WxWidgetIdHelper##::##CLASSNAME##_##MIN_ID,

#define END_WXWIDGET_ID_ENUM(CLASSNAME) CLASSNAME##_##MAX_ID }; \
  WxWidgetIdHelper::MaxIdCheck< \
  ( CLASSNAME##_##MAX_ID>WxWidgetIdHelper::CLASSNAME##_##MAX_ID ) > \
  INCREASE##_##CLASSNAME##_##MAX_ID_in_WxWidgetIdHelper_h;

VZ. VZ. · Accepted Answer · 2013-05-27T14:30:24

There is no universal answer but I think you should keep the following points in mind:

The IDs don't need to be globally unique, they only need to be unique inside each top level window. In a typical program, each dialog is represented by its own class so all the IDs in it are under control of this class only, allowing you not to care at all about what all the rest of the program does.
You can, and IMHO should, avoid using IDs completely for all the controls. The only place where the IDs are too convenient to keep them are the menu items as there is no object associated with them (you can't bind to a wxMenuItem). But for all the controls, it's better to simply call control->Bind() in which case you don't need to specify the ID at all as this control is only ever going to get the events for itself. And while it's really simple to replace event table macros with calls to Bind(), you don't even have to do it for your existing event tables as you don't have any ID conflicts in them, presumably -- so all you need to do is to use Bind() for the new event handlers.
If you use XRC -- and, again, IMHO there is no reason not to -- then all your IDs are strings specified in the XRC files and keeping strings distinct is, of course, much simpler than keeping integer IDs distinct, so this problem doesn't arise at all then. Notably, defining your menus in XRC takes care of one case in which IDs are really convenient to use.

TL;DR Don't use IDs at all except for the menu items, define them in XRC if you have to use them.

WxWidget ID issue

1 Answers