1) I had to change the following line:
2) The event structure in my version of Gtk renamed key to keyval so I change this:
switch( event->key )
to the following:
switch( event->keyval )
I'm really sorry for this. I should get into habit of proof-reading my posts before clicking "Submit" button.
3) I have my program set up so the callback functions are stored in callbacks.c and their definitions (not sure if that's the correct term) are stored in callbacks.h. When I tried using the static keyword as listed I received the following 2 errors:
callbacks.c:1538: warning: â€˜on_main_window_key_press_eventâ€™ defined but not used
callbacks.h:81: warning: â€˜on_main_window_key_press_eventâ€™ declared â€˜staticâ€™ but never defined
I tried fixing these errors using a method akin to using an ax to trim your fingernails: I changed it from static gboolean to void and removed all the return calls. It compiled warning-free but my program then would respond only to the keys I had listed in my switch statement block. If the GTKEntry widget had the focus, the code I had programmed for a particular key would run correctly but it would also add the character for that key to the entry string.
My final and less drastic solution to those warnings was to put back in the return calls and change the type from void to just gboolean, simply dropping the static keyword from the original code. That got me the result I needed. The keys I include in my switch statement block respond to my code and are not passed through to the entry field, and all other keys perform their normal functions.
So I have just a couple of follow-up questions: First, why was the function defined as static? Am I likely to have unseen troubles by removing it? Second, what happens if you return (FALSE) after the character specific code rather than return (TRUE)? (I might test that last question myself someday, but I thought I would ask in case someone has already tested and can just reply.)
First, static/non-static functions. Static symbols (functions, variables) are not exported from objects and are thus hidden from linker. This is why you've got those errors. Simply removing 'static' keyword from function declaration and definition (declarations are placed inside header file, definitions are placed inside C file) should resolve this linking problem.
I declared function as static simply because most of the sample code I write for this forum is composed of single C file and thus no exported symbols are needed (apart from main() function, that is). Omitting static keyword will not get you into any trouble at all and is actually required for your code to work correctly.
Now about those return values. If you look at the GtkWidget's signals, you'll notice that there is quite a few of them named <something>-event. This signals are wrappers around underlying windowing system events and their callback functions should have prototypes like this:
cb_func( GtkWidget *w,
gpointer d );
Return value of callback is really important here, since it controls propagation of this event further down the widget tree. Returning FALSE indicates that you didn't handle this event and so event should be propagated further. Returning TRUE will tell GTK+ that you handled this event and propagation stops.
For example, let's say that you handle '+' and '-' inside your switch. Focus is inside your entry and you press '7'. This triggers 'key-press-event' of your window. You check for '7' in your switch and since you don't need to handle it, your callback returns FALSE. Because event hasn't been handled, it's propagated further down to GtkEntry, whose 'key-press-event' is now emitted and default handler will insert character.
Now you press '+'. Again, 'key-press-event' of your window is triggered and because now your switch statement will handle it and return TRUE. Since you indicated that you handled this event, no propagation happens and signal chain stops. GtkEntry doesn't receive this event and thus '+' is not inserted.
Hopefully, you'll be able to make some sense out of my post (I'm having some troubles concentrating right now thanks to my 2 moths old son and his "everything is eatable" philosophy).