I'm using GTK+ in my paid work, which is being cool because I like this library. It's not the first time I use it for paid work, and I like these opportunities to learn more about it and possibly report bugs. It's not easy to find bugs in such a widely used library, so much of them end up being simple cosmetic mistakes, like this one. Some others are only a question of interpretation, like this other, which even when I submitted a patch, it was not applied.

Yesterday I couldn't make popup-menu create a, well, popup menu. It was working with button-press-event, but not with popup-menu. I created a small code sample to illustrate this problem and asked about it in #pygtk@irc.gimp.org --- yes, I'm using Python:

import gtk
import gobject

def menu():
  item = gtk.ImageMenuItem('gtk-add')
  item.show()

  menu = gtk.Menu()
  menu.add(item)

  return menu

def on_view_popup_menu(obj, *data):
  print 'popup-menu'
  menu().popup(None, None, None, 0, 0)

def on_view_button_press_event(obj, *data):
  print 'button-press-event'
  menu().popup(None, None, None, 0, 0)

store = gtk.ListStore(gobject.TYPE_STRING)
store.append(('teste',))

view = gtk.TreeView(store)
view.append_column(gtk.TreeViewColumn('Coluna', gtk.CellRendererText(), text=0))
view.connect('button-press-event', on_view_button_press_event)
view.connect('popup-menu', on_view_popup_menu)
view.show()

window = gtk.Window()
window.add(view)
window.show()

gtk.main()

When I clicked in the window, with any button in this case, 'button-press-event' is printed to stdout and the menu is displayed. When I press the Menu key, or Shift+F10, 'popup-menu' is printed to stdout, but the menu is not displayed. After getting no response in #pygtk, I decided to try #gtk+. Before that, I thought about trying the same problem in C to see if it was not a problem in the bindings, or in how I was using it. The code:

#include <gtk/gtk.h>

GtkMenu *menu() {
  GtkImageMenuItem *image_menu_item =
      GTK_IMAGE_MENU_ITEM(
          gtk_image_menu_item_new_from_stock(GTK_STOCK_ADD, NULL));
  gtk_widget_show(GTK_WIDGET(image_menu_item));

  GtkMenu *menu = GTK_MENU(gtk_menu_new());
  gtk_container_add(GTK_CONTAINER(menu), GTK_WIDGET(image_menu_item));

  return menu;
}

void on_tree_view_popup_menu(GtkWidget *widget, gpointer user_data) {
  printf("popup-menu\n");
  gtk_menu_popup(
      menu(), NULL, NULL, NULL, NULL, 0, gdk_event_get_time(NULL));
}

void
on_tree_view_button_press_event(
  GtkWidget *widget, GdkEventButton *event, gpointer user_data) {
  printf("button-press-event\n");
  gtk_menu_popup(
      menu(), NULL, NULL, NULL, NULL, 0, gdk_event_get_time(NULL));
}

int main(int argc, char **argv) {
  gtk_init(&argc, &argv);

  GtkListStore *list_store = gtk_list_store_new(1, G_TYPE_STRING);
  GtkTreeIter iter;
  gtk_list_store_append(list_store, &iter);
  gtk_list_store_set(list_store, &iter, 0, "teste", -1);

  GtkTreeView *tree_view =
      GTK_TREE_VIEW(
          gtk_tree_view_new_with_model(GTK_TREE_MODEL(list_store)));
  gtk_tree_view_append_column(
      tree_view,
      gtk_tree_view_column_new_with_attributes(
          "Coluna", gtk_cell_renderer_text_new(), "text", 0, NULL));
  g_signal_connect(
      tree_view, "popup-menu", G_CALLBACK(on_tree_view_popup_menu), NULL);
  g_signal_connect(
      tree_view,
      "button-press-event",
      G_CALLBACK(on_tree_view_button_press_event),
      NULL);
  gtk_widget_show(GTK_WIDGET(tree_view));

  GtkWindow *window = GTK_WINDOW(gtk_window_new(GTK_WINDOW_TOPLEVEL));
  gtk_container_add(GTK_CONTAINER(window), GTK_WIDGET(tree_view));
  gtk_widget_show(GTK_WIDGET(window));

  gtk_main();
}

Wow. The difference between the codes is impressive. I'm not that used to code in GTK+ using C, and I may have missed something here, but the C code is so verbose that I get tired only by looking at it. I'm glad we have other languages, and GTK+ bindings for them. As expected, the behavior was the same, and I asked in #gtk+ and got no answer.

Yes, I did read the documentation before asking, and no, I didn't read it carefully enough. Maybe because of coming from Python, I didn't checked very much the type of the callback function for the signals, and didn't notice the point about the return value: "Returns: TRUE if a menu was activated". And that was not where I was looking for the problem, since I thought the return value was usually related to the treatment of the signal by another functions. Anyway, I changed the type of on_tree_view_popup_menu to return gboolean and returned TRUE. It works! I also updated the type of on_tree_view_button_press_event to do the same, just for compliance. In Python, a simple return True would do it.

I know I could use the event parameter in on_tree_view_button_press_event, but the point was exactly to run the same code and see if it would work in one case and not in the other, as happened.