How to customize GtkCellRendererCombo ?

[Miroslav Rajcic <support notecasepro com>]

I am trying to customize GtkCellRendererCombo so that the items in the 
combo box have different colors.
Documentation indicates that this is supposed to be done through 
"editing-started" signal handler, but I failed to do it.

My sample is given below.
When gtk_cell_layout_set_cell_data_func or gtk_cell_layout_add_attribute 
call is being made, GTK issues error:
"gtk_combo_box_cell_layout_set_cell_data_func: assertion `info != NULL' 
failed".
And the coloring doesn't work.

Any tips?

Regards,
  Miroslav

PS. Code:

#include <gtk/gtk.h>

GtkWidget *window1;
GtkListStore *store;

void TaskStatusComboCellData(GtkCellLayout *cell_layout, GtkCellRenderer 
*cell, GtkTreeModel *tree_model, GtkTreeIter *iter, gpointer data)
{
    //get item index
    GtkTreePath *path = gtk_tree_model_get_path(tree_model, iter);
    gint* arrIndices = gtk_tree_path_get_indices(path);
    int nIdx = arrIndices[0];
    gtk_tree_path_free(path);

    //now set correct color for each item
    switch (nIdx){
    case 0:
        g_object_set(G_OBJECT(cell), "foreground", "red", NULL);
        break;
    case 1:
        g_object_set(G_OBJECT(cell), "foreground", "blue", NULL);
        break;
    }
}

void on_tree_cell_combo_editing_start(GtkCellRenderer *renderer, 
GtkCellEditable *editable, gchar *path, gpointer user_data)
{
    //set colors for combo box entries
    if (GTK_IS_COMBO_BOX(editable))
    {
        //refresh latest colors
        GtkComboBox *combo = GTK_COMBO_BOX(editable);
        //TOFIX
        gtk_cell_layout_set_cell_data_func(GTK_CELL_LAYOUT(combo), 
renderer, TaskStatusComboCellData, NULL, NULL);
        //gtk_cell_layout_add_attribute(GTK_CELL_LAYOUT(combo), 
renderer, "foreground", 2);
    }
}

GtkWidget* create_main_win ()
{
    GtkWidget *vbox1;
    GtkWidget *scrolledwindow1;
    GtkWidget *treeview4;

    window1 = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title (GTK_WINDOW (window1), "Test");
    gtk_window_set_default_size (GTK_WINDOW (window1), 500, 350);

    vbox1 = gtk_vbox_new (FALSE, 0);
    gtk_widget_show (vbox1);
    gtk_container_add (GTK_CONTAINER (window1), vbox1);

    scrolledwindow1 = gtk_scrolled_window_new (NULL, NULL);
    gtk_widget_show (scrolledwindow1);
    gtk_container_add (GTK_CONTAINER (vbox1), scrolledwindow1);
    gtk_scrolled_window_set_policy (GTK_SCROLLED_WINDOW 
(scrolledwindow1), GTK_POLICY_AUTOMATIC, GTK_POLICY_AUTOMATIC);

    //create tree view
    store = gtk_list_store_new(2, G_TYPE_STRING, G_TYPE_STRING);
      treeview4 = gtk_tree_view_new_with_model(GTK_TREE_MODEL(store));
    g_object_unref (G_OBJECT (store));  //tree now holds reference
    gtk_widget_set_size_request(treeview4, -1, 150);

    //create list view columns
    gtk_tree_view_set_headers_visible(GTK_TREE_VIEW(treeview4), TRUE);
    gtk_tree_view_set_headers_clickable (GTK_TREE_VIEW(treeview4), TRUE);
    gtk_tree_view_set_enable_search(GTK_TREE_VIEW(treeview4),FALSE);
    gtk_widget_show (treeview4);
    gtk_container_add (GTK_CONTAINER (scrolledwindow1), treeview4);

    GtkTreeViewColumn *col = gtk_tree_view_column_new();
    gtk_tree_view_column_set_title(col, "Title");
    gtk_tree_view_column_set_clickable(col, TRUE);    //allow column 
header clicks
    gtk_tree_view_column_set_sizing (col, GTK_TREE_VIEW_COLUMN_FIXED);
    gtk_tree_view_column_set_resizable(col, TRUE);
    gtk_tree_view_column_set_fixed_width(col, 100);

    GtkCellRenderer *renderer = gtk_cell_renderer_text_new();
    gtk_tree_view_column_pack_start(col, (GtkCellRenderer *)renderer, 
TRUE);
    gtk_tree_view_column_add_attribute(col, renderer, "text", 0);
    gtk_tree_view_append_column(GTK_TREE_VIEW(treeview4), col);

    col = gtk_tree_view_column_new();
    gtk_tree_view_column_set_title(col, "Type");
    gtk_tree_view_column_set_clickable(col, TRUE);    //allow column 
header clicks
    gtk_tree_view_column_set_sizing (col, GTK_TREE_VIEW_COLUMN_FIXED);
    gtk_tree_view_column_set_resizable(col, TRUE);
    gtk_tree_view_column_set_fixed_width(col, 150);

    renderer = gtk_cell_renderer_combo_new();
    gtk_tree_view_column_pack_start(col, renderer, TRUE);
    gtk_tree_view_column_add_attribute(col, renderer, "text", 1);
    gtk_tree_view_append_column(GTK_TREE_VIEW(treeview4), col);

    //add combo with values
    GtkListStore *store1 = gtk_list_store_new(2, G_TYPE_STRING, 
G_TYPE_STRING);    //text, color
    GtkTreeIter iter;
    gtk_list_store_append(store1, &iter);
    gtk_list_store_set(store1, &iter, 0, "Type 1 (red)", -1);
    gtk_list_store_append(store1, &iter);
    gtk_list_store_set(store1, &iter, 0, "Type 2 (blue)", -1);
    gtk_list_store_append(store1, &iter);
    gtk_list_store_set(store1, &iter, 0, "Type 3 (green)", -1);

    g_object_set(renderer, "model", store1, "text-column", 0, 
"has-entry", FALSE, "editable", TRUE, (char *)NULL);
    g_signal_connect(renderer, "editing-started", 
G_CALLBACK(on_tree_cell_combo_editing_start), NULL);

    gtk_widget_show_all(window1);

    g_signal_connect(window1, "destroy", G_CALLBACK(gtk_main_quit), NULL);

    return window1;
}

void fill_sample_data()
{
    GtkTreeIter iter;
    gtk_list_store_append(store, &iter);
    gtk_list_store_set(store, &iter, 0, "Item1", 1, "Item1 type", -1);

    gtk_list_store_append(store, &iter);
    gtk_list_store_set(store, &iter, 0, "Item2", 1, "Item2 type", -1);
}

void GtkLogHandler(const gchar *log_domain, GLogLevelFlags log_level, 
const gchar *message, gpointer user_data)
{
    printf("GTK [%d]: %s\n", log_level, message);
}

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

    //register logging
    GLogLevelFlags logFlags = (GLogLevelFlags)(G_LOG_LEVEL_MASK); //all
    g_log_set_handler(G_LOG_DOMAIN, logFlags, GtkLogHandler, NULL);
    g_log_set_handler("Gtk", logFlags, GtkLogHandler, NULL);
    g_log_set_handler("Gdk", logFlags, GtkLogHandler, NULL);
    g_log_set_handler("GLib", logFlags, GtkLogHandler, NULL);

    window1 = create_main_win ();

    fill_sample_data();

    gtk_main ();

    return 0;
}

#ifdef _WIN32
#include <windows.h>
int APIENTRY WinMain( HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR lpCmdLine, int nCmdShow)
{
    return main( __argc, __argv );
}
#endif