Re: what's the best way to handle variables and objects?

[Wallace Owen <wallace owen L-3Com com>]

My reply's in the body (I ain't no top-poster!):

On Wed, 2006-03-15 at 22:57 +0100, Andreas Kotowicz wrote:
> On Wed, 2006-03-15 at 13:44 -0500, John (J5) Palmieri wrote:
> > You can create a generic struct but more often than not there is an
> > application object or struct that the application developer creates
> > which holds all the public variables he or she would care about which is
> > passed as userdata to things like g_signal_connect.  
>
> sorry, but I don't exactly understand what you mean. Could you maybe
> give me an example of how the application object and the interaction
> would look like? would this application object also hold all the labels
> and entry fields which might change?
>
> but maybe I do understand you. what I use here is following:
>
> main.c:
>
> #include <gtk/gtk.h>
> #include "interface.h"
> int main (int argc, char *argv[])
> {
>
>   GtkWidget *window1;
>
>   gtk_init(&argc, &argv);
>
>   window1 = create_window1 ();
>   gtk_widget_show_all(window1);
>
>   gtk_main();
>   return 0;
> }
>
>
> interface.h:
> #include <gtk/gtk.h>
>
> GtkWidget* create_window1 (void);
>
> interface.c:
>
> #include "callbacks.h"
> #include "interface.h"
>
> GtkWidget*
> create_window1 (void)
> {
>   GtkWidget *window;
>   GtkWidget *vbox;
>   GtkWidget *progressbar;
>   GtkWidget *button_start;
>   GtkWidget *spin_sec;
>   GtkWidget *spin_min;
>
>   window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
>   gtk_window_set_title(GTK_WINDOW(window), "Window");
>   g_signal_connect(G_OBJECT(window), "destroy", 
>   G_CALLBACK(destroy_window_cb), NULL);
>   
>   /* vbox for whole window */
>   vbox = gtk_vbox_new(FALSE, 6);
>   gtk_container_add(GTK_CONTAINER(window), vbox);
>
>   /* put progressbar at the top of the window */
>   progressbar = gtk_progress_bar_new();
>   gtk_box_pack_start(GTK_BOX(vbox), progressbar, TRUE, TRUE, 12);
>
>   /* entry field for number of seconds */
>   spin_sec = gtk_spin_button_new_with_range(0, 59, 1);  
>   gtk_box_pack_start(GTK_BOX(vbox), spin_sec, FALSE, FALSE, 0);  
>
>   
>   button_start = gtk_button_new_with_mnemonic("_Start");
>   gtk_box_pack_start(GTK_BOX(vbox), button_start, FALSE, FALSE, 0);
>
>   g_signal_connect(GTK_BUTTON(button_start), "clicked", 
>   G_CALLBACK(start_timer_cb), progressbar);
>   
>   return window;
> }
>
> is this what you mean by application object? here comes my problem now:
> g_signal_connect on button_start only passes on the progressbar object
> to start_timer_cb(). but I also want to have the user input from
> spin_sec in this function. so how can I get a grip on both of these (or
> even more) variables in start_timer_cb() ?

Define a struct that has as it's member fields all the values you want
accessible to the callback, including the progressbar, spin_sec, etc:

struct MyUserData
{
    GtkWidget *progress_bar;
    GtkWidget *spin_sec;
};

Allocate one of these on the heap (note: I'm using C++, so new's what I
use for this):

MyUserData *myData = new MyUserData;

myData->progress_bar = progressbar;
myData->spin_sec = spin_sec;

Pass the allocated storage as the last parm to g_signal_connect.

g_signal_connect(GTK_BUTTON(button_start), "clicked", G_CALLBACK
(start_timer_cb), myData);

In the callback, cast the pointer to the user-supplied parm to the type
of your struct and access it's members as needed:

void start_timer_cb(GtkObject *window, void *data)
{
    MyUserData *myData = (MyUserData*)data;

    // the progressbar is myData->progress_bar, etc.
    // ...
}

Remember to return the storage to the heap when you're done using it.


  // Wally

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