What do you use the callbackData for ?

[gdargaud]

OK, this is a dumb question, but generally speaking, what do you use the callbackData for ?

Yes, I know I can use:

    SetCtrlAttribute (panel, control, ATTR_CALLBACK_DATA, &SomeStaticData);

And recover its value inside the callback function with:
    typeofmydata Val=*(typeofmydata*)callbackData;

But except sometimes in the case of deferred callbacks, I don't see a use for it.

[RobertoBozzolo]

I use callbackData parameter on settings panels: controls on that panel are all set with callbackData pointed to the save button, which initially is dimmed. When the user modifies a control, the associated callback enables the save button, so that I know that modifications have made and can trap this occurrence on the exit button callback. This way I can set a single function for all controls on the panel.

Some code will explain this paradigm better. When I load a settings panel I initialize all controls  this way:

int CVICALLBACK loadSettingsPanel (int panel, int control, int event,
		void *callbackData, int eventData1, int eventData2)

{
	int	tmpH, aryH;

	if (event != EVENT_COMMIT) return 0;

	// Load panel
	tmpH = LoadPanel (0, UIR, PANEL);
	if (tmpH < 0) {
		// Warn the user for error
		goto Error;
	}

	// Initialize controls
	SetCtrlAttribute (tmpH, PANEL_NUMERIC, ATTR_CALLBACK_DATA, (void *)PANEL_SAVEBTN);
	SetCtrlAttribute (tmpH, PANEL_STRING,  ATTR_CALLBACK_DATA, (void *)PANEL_SAVEBTN);
	// Repeat for all controls...

	// In case controls are grouped into arrays things are simpler:
	aryH = GetCtrlArrayFromResourceID (tmpH, CTRLARRAY);
	SetCtrlArrayAttribute (aryH, ATTR_CALLBACK_DATA, (void *)PANEL_SAVEBTN);

	// Initialize 'Exit' button
	SetCtrlAttribute (tmpH, PANEL_QUITBTN, ATTR_CALLBACK_DATA, (void *)PANEL_SAVEBTN);

	// Other stuff here...

	// Show pannel
	InstallPopup (tmpH);

Error:
	return 0;
}

(I know I could iterate on all controls in a panel but I don't know whether this parameter can be set for all control types -including decorations and so on- so to avoid problems I manually set it for active controls only).

This is the generic callback which can be associated to whichever control type you want:

int CVICALLBACK valueModified (int panel, int control, int event,
		void *callbackData, int eventData1, int eventData2)
{
	if (event != EVENT_VAL_CHANGED) return 0;

	// Enable 'Save' button
	if (callbackData) SetInputMode (panel, (int)callbackData, 1);

	return 0;
}

This is the exit button callback:

int CVICALLBACK exitCallback (int panel, int control, int event,
		void *callbackData, int eventData1, int eventData2)
{
	int		dimmed;

	if (event != EVENT_COMMIT) return 0;

	if (callbackData) {
		GetCtrlAttribute (panel, (int)callbackData, ATTR_DIMMED, &dimmed);
		if (!dimmed) {
			// Ask the user if he wants to save changes: if yes return 0
		}
	}
	DiscardPanel (panel);

	return 0;
}

The save button callback must dim itself on success to prevent further confirm popups on exit.

I find this framework handy since it permits to have a single callback for all similar control even on different panels.