Why are Gdk::Pixbufs not visible in Gtk::TreeView? - treeview

Question

After spending a long time searching for an answer, I hope someone can help me with this problem. I'm trying to use gtkmm (version 3.14.0) and glade (version 3.18.3) on a Fedora 21 system to create a Gtk::TreeView/Gtk::ListStore with many small images. I can easily place stock icons in the list, but adding Gdk::Pixbuf objects seems to go wrong. No error or warning messages are shown, but the Gdk::Pixbuf image is not shown.
To show the problem, I've created a minimal working example (the code of the program and the glade file included at the end). Running this program should open a small window with the Gtk::TreeView with two "gtk-apply" icons. In the first column should be the icon added as Gdk::Pixbuf, in the second column should be the stock icon. However, when I run the program, the first column remains empty. There are no compile or run-time errors or warnings.
My final application will display a matrix of about 100 rows and about 35 columns of mostly tiny icons allowing a quick overview of activities done on the different days of a month. None of these icons will be stock icons.
Extra Information: Following the program execution using a debugger, I found that the Gtk::ListStore's first column wants data of type gtkmm__GdkPixbuf. The type of pb in the line row[cols.m_pb] = pb is GdkPixbuf. The type GdkPixbuf cannot be converted to gtkmm__GdkPixbuf automatically, causing the value to be set to 0 (NULL). Obviously this does not solve the problem, but might help to solve the problem.
Thanks for the help and best wishes for 2015,
Wim
This is the file mwe.glade:
<?xml version="1.0" encoding="UTF-8"?>
<!-- Generated with glade 3.18.3 -->
<interface>
<requires lib="gtk+" version="3.12"/>
<object class="GtkAccelGroup" id="accelgroup1"/>
<object class="GtkApplicationWindow" id="mainwindow">
<property name="can_focus">False</property>
<property name="show_menubar">False</property>
<child>
<object class="GtkGrid" id="mainbox">
<property name="visible">True</property>
<property name="can_focus">False</property>
<property name="orientation">vertical</property>
<child>
<object class="GtkTreeView" id="treattree">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="vexpand">True</property>
<property name="hscroll_policy">natural</property>
<property name="model">treatstore</property>
<property name="rules_hint">True</property>
<property name="search_column">0</property>
<property name="fixed_height_mode">True</property>
<child internal-child="selection">
<object class="GtkTreeSelection" id="sel1"/>
</child>
<child>
<object class="GtkTreeViewColumn" id="col1">
<property name="sizing">fixed</property>
<property name="fixed_width">32</property>
<property name="title">1</property>
<child>
<object class="GtkCellRendererPixbuf" id="cell1">
<property name="width">16</property>
<property name="height">16</property>
</object>
<attributes>
<attribute name="pixbuf">0</attribute>
</attributes>
</child>
</object>
</child>
<child>
<object class="GtkTreeViewColumn" id="col2">
<property name="sizing">fixed</property>
<property name="fixed_width">32</property>
<property name="title">2</property>
<child>
<object class="GtkCellRendererPixbuf" id="cell2"/>
<attributes>
<attribute name="stock-id">1</attribute>
</attributes>
</child>
</object>
</child>
</object>
<packing>
<property name="left_attach">0</property>
<property name="top_attach">0</property>
</packing>
</child>
</object>
</child>
</object>
<object class="GtkListStore" id="treatstore">
<columns>
<!-- column-name col1 -->
<column type="GdkPixbuf"/>
<!-- column-name col2 -->
<column type="gchararray"/>
</columns>
</object>
</interface>
The file mwe.cpp:
#include <gtkmm.h>
namespace ws
{
class App : public Gtk::Application
{
protected:
App() : Gtk::Application("nl.mwe.mwe"), m_mainwindow(0)
{
Glib::set_application_name("MWE");
}
public:
static Glib::RefPtr<App> create(int &argc, char **&argv)
{
return Glib::RefPtr<App>(new App());
}
void init(Glib::RefPtr<Gtk::Builder> builder);
int run()
{
return Gtk::Application::run(*m_mainwindow);
}
private:
Gtk::ApplicationWindow *m_mainwindow;
};
// Definition of the column references
class ModelColumns : public Gtk::TreeModelColumnRecord
{
public:
ModelColumns()
{
add(m_pb);
add(m_stock);
}
Gtk::TreeModelColumn<Glib::RefPtr<Gdk::Pixbuf> > m_pb;
Gtk::TreeModelColumn<Glib::ustring> m_stock;
};
static ModelColumns col;
} // End namespace ws
/**
* \brief Initialize the app
* \param[in] builder The builder object
*
* Here is where the list store is populated with the Gdk::Pixbuf
*/
void ws::App::init(Glib::RefPtr<Gtk::Builder> builder)
{
builder->get_widget("mainwindow", m_mainwindow);
m_mainwindow->show();
Glib::RefPtr<Gtk::ListStore> store =
Glib::RefPtr<Gtk::ListStore>::cast_static(
builder->get_object("treatstore"));
Gtk::TreeModel::Row row = *store->append();
// The line below loads the stock icon as a pixbuf.
Glib::RefPtr<Gdk::Pixbuf> pb =
Gtk::IconTheme::get_default()->load_icon("gtk-apply", 16);
row[col.m_pb] = pb;
row[col.m_stock] = "gtk-apply";
}
int main (int argc, char *argv[])
{
Glib::RefPtr<ws::App> myapp = ws::App::create(argc, argv);
Glib::RefPtr<Gtk::Builder> builder = Gtk::Builder::create();
builder->add_from_file("mwe.glade");
myapp->init(builder);
return myapp->run();
}

Answer 1

After finding the problems in the types as shown in the Extra Information
section in the question, I decided to create the store by hand. The definition
of the GtkListStore was removed from the glade file. The ws::App::init()
method was changed to:
void ws::App::init(Glib::RefPtr<Gtk::Builder> builder)
{
builder->get_widget("mainwindow", m_mainwindow);
Gtk::TreeView *treeview = 0;
builder->get_widget("treattree", treeview);
Glib::RefPtr<Gtk::ListStore> store =
Gtk::ListStore::create(col);
treeview->set_model(store);
Gtk::TreeModel::Row row = *store->append();
// The line below loads the stock icon as a pixbuf.
Glib::RefPtr<Gdk::Pixbuf> pb =
Gtk::IconTheme::get_default()->load_icon("gtk-apply", 16);
row[col.m_pb] = pb;
row[col.m_stock] = "gtk-apply";
m_mainwindow->show();
}
Although this is not as flexible as hoped, it does fix the problem.