[SOLVED] GTK with C++ sending multiple GObjects to a callback function through a GObject

anon112 · 04-03-2016, 09:33 AM

I'm trying to send multiple arguments to a GTK callback function by adding them to a GObject as such:

Code:

GObject* EntryBoxes;
g_object_set_data(EntryBoxes,"Text",Text);
g_object_set_data(EntryBoxes,"Text2",Text2);
g_object_set_data(EntryBoxes,"ComboBox",ComboBox);

where Text, Text2, and ComboBox are all GObjects.

In my callback function though, I am unable to access the data in my GObject. I am accessing using the following method:

Code:

void CallbackFunction1(GtkWidget* W, gpointer data)
{
    GObject* Entry1 = G_OBJECT(g_object_get_data(G_OBJECT(data),"Text"));
};

however when I try to compile and run, I get a segfault when I try to run the set_data commands.

Is there something I'm missing?

anon112 · 04-03-2016, 11:00 AM

Solved this myself;

Basically, what I'm doing now is defining a GObject** for the data being sent and assigning a size with g_new(...). Then I am assigning the array elements of my GObject** accordingly and sending it as my data to the callback function.

In the callback function, I assign GObject** data_i_want = (GObject**)data and treat data_i_want as a normal array (so I can access the individual GObject* members as data_i_want[i]).

This is slightly different than what I was going for with g_object_set_data, but it works. If anyone would like to suggest a method for using g_object_set_data, it would still be appreciated.

ntubski · 04-03-2016, 11:34 AM

Quote:

Originally Posted by kev717

however when I try to compile and run, I get a segfault when I try to run the set_data commands.

Is there something I'm missing?

It sounds like you didn't allocate any memory for EntryBoxes.

anon112 · 04-03-2016, 11:50 AM

Does g_object_set_data require memory allocation? In the solution I posted g_new handled that... Also there's no mention of memory allocation for the function documentation.

https://developer.gnome.org/gobject/...bject-set-data

ntubski · 04-03-2016, 12:23 PM

A pointer needs something to point to. In the code you posted:

Code:

GObject* EntryBoxes;
g_object_set_data(EntryBoxes,"Text",Text);
g_object_set_data(EntryBoxes,"Text2",Text2);
g_object_set_data(EntryBoxes,"ComboBox",ComboBox);

EntryBoxes is uninitialized so it's pointing to some random block of memory. Attempting to use this pointer will lead to undefined behaviour, such as segfaulting.

anon112 · 04-03-2016, 12:56 PM

That makes sense. When I allocate memory for EntryBoxes, I get an error while running the program of

Quote:

g_object_set_data: assertion 'G_IS_OBJECT (object)' failed

ntubski · 04-03-2016, 01:24 PM

Ah, looks like you also need to initialize to a valid GObject value. I'm not really familiar with GTK/Glib stuff, but I think you want something along the lines of

Code:

GObject* EntryBoxes = g_object_new(G_TYPE_OBJECT, NULL);

X-LFS-2010 · 04-03-2016, 09:33 PM

yes but GTK's behavior changes (infact it plain drops support for whole apps to be working any longer)

why not do it the C way, make things simple for poor GTK, give it one object to which you have indexed (by struct offset, or other allocation), your 'stuff'

do be wary under a client/server system there's a difference between memory allocated and accessed on the client, on the server, as transfered and seen between the two. classic mistake

so if i'm using X11 and wish to draw i allocate memory on the server (remote side) and sent draw commands (such as move) and thus, the data in the window does not need to be tranfered to the client for processing and back to the server

also note on broken systems (ie, win32), callbacks are at times done MULTIPLY - so your program should be INDEPENDANT of callbacks (able to avert or handle), and ready to receive a callback during a callback (re-entrant function programming)

anon112 · 04-04-2016, 08:01 AM

So using an array of pointers is a better option then?

I'm mostly doing my window event processing through my callback functions, so if I need to send a draw command to the window then the callback function handles everything I need it to do.

Thanks for the heads-up on the win32 platform.