How do I make a GtkBuilderListItemFactory closure to access its function in code?

Development
1

Hi,

I’m currently building an app based on the default “Gnome Application model” in Gnome Builder. My app will include a listview as its main component.

While trying to display the content of a basic GtkDirectoryList, I cannot get my factory to work with closure functions. I’ve spent the most part of the last two days on this problem, so I resort to asking help here before going crazy.

I simply replaced the main “label” container with this in the ui file:

[…]
    <property name="content">
      <object class="GtkScrolledWindow" id="scrolledwindow">
        <property name="hexpand" >TRUE</property>
        <property name="vexpand" >TRUE</property>
        <child>
          <object class="GtkListView" id="listview">
            <property name="model">
              <object class="GtkSingleSelection" id="singleselection">
                <property name="model">
                  <object class="GtkDirectoryList" id="directorylist">
                    <property name="attributes">standard::name,standard::icon,standard::content-type</property>
                  </object>
                </property>
              </object>
            </property>
            <signal name="activate" handler="listview_activate"/>
            <property name="factory">
              <object class="GtkBuilderListItemFactory">
                <property name="bytes">
<![CDATA[
<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <template class="GtkListItem">
    <property name="child">
      <object class="GtkBox">
        <property name="orientation">GTK_ORIENTATION_HORIZONTAL</property>
        <property name="spacing">20</property>
        <child>
          <object class="GtkImage">
            <binding name="gicon">
              <closure type="GIcon" function="get_icon">
                <lookup name="item">GtkListItem</lookup>
              </closure>
            </binding>
          </object>
        </child>
        <child>
          <object class="GtkLabel">
            <property name="hexpand">TRUE</property>
            <property name="xalign">0</property>
            <binding name="label">
              <closure type="gchararray" function="get_file_name">
                <lookup name="item">GtkListItem</lookup>
              </closure>
            </binding>
          </object>
        </child>
      </object>
    </property>
  </template>
</interface>
]]>
                </property>
              </object>
            </property>
          </object>
        </child>
      </object>
    </property>
[…]

Then I included the widgets in my code and created the needed functions (get_icon and get_file_name):

[…]

struct _MyAppWindow
{
  AdwApplicationWindow  parent_instance;

  /* Template widgets */
  GtkSearchEntry      *searchentry;
  GtkScrolledWindow   *scrolledwindow;
  GtkListView         *listview;
  GtkSingleSelection  *singleselection;
  GtkDirectoryList    *directorylist;
};

static GIcon *
get_icon (GtkListItem *item, GFileInfo *info) {
  GIcon *icon;
   /* g_file_info_get_icon can return NULL */
  icon = G_IS_FILE_INFO (info) ? g_file_info_get_icon (info) : NULL;
  return icon ? g_object_ref (icon) : NULL;
}

static char *
get_file_name (GtkListItem *item, GFileInfo *info) {
  return G_IS_FILE_INFO (info) ? g_strdup (g_file_info_get_name (info)) : NULL;
}

static void
myapp_window_class_init (MyAppWindowClass \*klass)
{
  GtkWidgetClass \*widget_class = GTK_WIDGET_CLASS (klass);
  
  gtk_widget_class_set_template_from_resource (widget_class, “/com/example/MyApp/myapp-window.ui”);
  gtk_widget_class_bind_template_child (widget_class, MyAppWindow, searchentry);
  gtk_widget_class_bind_template_child (widget_class, MyAppWindow, scrolledwindow);
  gtk_widget_class_bind_template_child (widget_class, MyAppWindow, listview);
  gtk_widget_class_bind_template_child (widget_class, MyAppWindow, singleselection);
  gtk_widget_class_bind_template_child (widget_class, MyAppWindow, directorylist);
}

static void
myapp_window_init (MyAppWindow *self)
{
  GFile *file;

  gtk_widget_init_template (GTK_WIDGET (self) );

  file = g_file_new_for_path (".");
  gtk_directory_list_set_file (GTK_DIRECTORY_LIST (self->directorylist), file);
  g_object_unref (file);
}

When I run the app, the factory fails to populate the listview (I do get empty rows created), with these errors (one per file) in logs:

Gtk-CRITICAL **: 21:48:55.247: Error building template for list item: .:0:0: No function named `get_icon`.

It is an error I encountered previously when building an app directly with gcc, but I could fix it by passing the gcc -Wl,--export-dynamic options.

Since Gnome Builder is using meson builds, I suppose I am missing a meson option somewhere, so how can I get my app to compile correctly ?

Thanks in advance

2

You’ll want to bind the callbacks with gtk_widget_class_bind_template_callback:

gtk_widget_class_bind_template_callback (widget_class, get_icon);
gtk_widget_class_bind_template_callback (widget_class, get_file_name);
3

Thanks a lot @monster . I can’t believe it is that simple, yet I didn’t see it in the documentation.

Shouldn’t the official documentation (Gtk.Expression) explicitly mention that those functions are to be treated as callbacks?

4

I’m indeed a bit surprised it isn’t mentioned anywhere (from what I can see). I’d say the best place to document it is at Building composite widgets from template XML, since that’s where signal callbacks are documented as well.

5

“Callback” does not mean “signal handler”: it means any function referred to by name in the UI definition file, and by pointer in the code.

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