Re: Inserting text in a text buffer using a callback function

[TORRI Vincent <Vincent Torri math u-bordeaux fr>]

On Sat, 2 Nov 2002, Horror Vacui wrote:

> I have the following problem: while trying to learn GTK, I decided to 
> create a button that should insert text in a scrolled window (more 
> exactly: into a text buffer in a scrolled window). I created a callback 
> for a function, and it wouldn't work. I transferred parts of code from 
> the function to main (so that it is inserted during the realisation of 
> the window), and that did work. The function behaves weird: before, the 
> program would just segfault when this button is clicked, now it returns 
> a Gtk-critical message saying that assertion GTK_IS_TEXT_BUFFER (buffer) 
> for the argument I passed to the function failed (I don't understand 
> that change either - I didn't change anything of significance). From 
> what I learned from learning programming, the error is probably 
> something very trivial, but it can take me days to sort out. Here are 
> the significant parts of code:
>
>    GtkWidget *view;
>    GtkTextBuffer *buffer;
>
>    button=gtk_button_new_with_label("text");   /*the button*/
>    g_signal_connect(G_OBJECT (button), "clicked", G_CALLBACK (text), 
> buffer);   /*connecting signal to callback*/
>
>    view=gtk_text_view_new();
>    buffer=gtk_text_view_get_buffer(GTK_TEXT_VIEW (view));   /*the buffer*/
>    gtk_text_buffer_set_text(buffer, "This is the text in the scrolled 
> window\n", -1);   /*inserting text, this works*/
>
> void text(GtkTextBuffer *buffer)    /*the callback function*/

the prototype of the callback function associated to the "clicked" signal 
is

  void user_function (GtkButton *button, gpointer user_data)

(from the API). You don't "insert" text in the GtkTextBuffer (as you 
could think), but in the GtkButton. 

Hope this helps

Vincent TORRI

> {
>    GtkTextIter iter;
>    gtk_text_buffer_get_iter_at_offset(buffer, &iter, 0);
>    gtk_text_buffer_insert(buffer, &iter, "This is the text in the 
> scrolled window\n", -1);   /*this doesn't work*/
> }
>
> Of course, I've already run the code through a debugger. The callback 
> works, the function text is called with pointer "buffer" as argument, it 
> is the correct one, it is the correct type inside the function. Yet it 
> doesn't work. I've also tried using exactly the same function that works 
> in main (gtk_text_buffer_set_text()) in the callback function: nothing. 
> I also thought about a conflict between the two variables with the same 
> name "buffer" (which should hardly matter) and tried giving them 
> different names: nothing. I'm quite stuck, I hope someone can help.
>
> Thanks in advance
> Horror Vacui
>
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-- 
TORRI Vincent
Mathematiques Appliquees Bordeaux                                                
Institut de Mathematiques                                                       
Universite Bordeaux 1                                                           
351 cours de la liberation                                                      
33 405 Talence cedex - France                                                   
                                                                                
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