GtkTreeView problem v2

#include <gtk/gtk.h>

static GtkWidget *tree_view;
static GtkWidget *btn_add_item;
static int row_count = 0;

static void btn_add_item_clicked(GtkWidget *button, gpointer data) {
    GtkListStore *model;
    GtkTreeIter iter;
    char text[50];

    model = (GtkListStore*) gtk_tree_view_get_model(GTK_TREE_VIEW(tree_view));
    gtk_list_store_append(model,
            &iter);

    sprintf(text,
            "%d",
            row_count + 1);
    gtk_list_store_set(model,
            &iter,
            0, g_strdup(text),
            -1);

    gtk_tree_view_set_model(GTK_TREE_VIEW(tree_view),
            GTK_TREE_MODEL(model));
}

static void content_renderer_edited(GtkCellRendererText *renderer, gchar *path,
        gchar *new_text, gpointer user_data) {
    GtkListStore *list_store;
    GtkTreeIter iter;
    GtkTreePath *tree_path;

    tree_path = gtk_tree_path_new_from_string(path);

    list_store = (GtkListStore*) gtk_tree_view_get_model(
            GTK_TREE_VIEW(tree_view));
    gtk_tree_model_get_iter(GTK_TREE_MODEL(list_store),
            &iter,
            tree_path);

    gtk_list_store_set(list_store,
            &iter,
            1, new_text,
            -1);

    gtk_tree_view_set_model(GTK_TREE_VIEW(tree_view),
            GTK_TREE_MODEL(list_store));
}

static GtkWidget *create_tree_view() {
    GtkWidget *grid;
    GtkWidget *scrolled_window;
    GtkListStore *list_store;
    GtkTreeViewColumn *label_col;
    GtkTreeViewColumn *content_col;
    GtkCellRenderer *content_renderer;

    list_store = gtk_list_store_new(2,
            G_TYPE_STRING,
            G_TYPE_INT);

    tree_view = gtk_tree_view_new();
    label_col = gtk_tree_view_column_new_with_attributes("Layer",
            gtk_cell_renderer_text_new(),
            NULL);
    content_renderer = gtk_cell_renderer_text_new();
    g_signal_connect(content_renderer,
            "edited",
            G_CALLBACK(content_renderer_edited),
            NULL);

    g_object_set(content_renderer,
            "editable", TRUE,
            NULL);

    content_col = gtk_tree_view_column_new_with_attributes("Content",
            content_renderer,
            NULL);

    gtk_tree_view_append_column(GTK_TREE_VIEW(tree_view),
            label_col);
    gtk_tree_view_append_column(GTK_TREE_VIEW(tree_view),
            content_col);

    gtk_tree_view_set_model(GTK_TREE_VIEW(tree_view),
            GTK_TREE_MODEL(list_store));

    scrolled_window = gtk_scrolled_window_new(NULL,
            NULL);
    gtk_container_add(GTK_CONTAINER(scrolled_window),
            tree_view);

    btn_add_item = gtk_button_new_with_label("Add");
    g_signal_connect(btn_add_item,
            "clicked",
            G_CALLBACK(btn_add_item_clicked),
            NULL);

    grid = gtk_box_new(GTK_ORIENTATION_VERTICAL,
            5);
    gtk_box_pack_start(GTK_BOX(grid),
            scrolled_window,
            TRUE,
            TRUE,
            5);
    gtk_box_pack_start(GTK_BOX(grid),
            btn_add_item,
            FALSE,
            FALSE,
            5);

    return grid;
}

int main(int argc, char **argv) {
    GtkWidget *window;
    GtkWidget *content_area;

    gtk_init(&argc, &argv);
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    g_signal_connect(window, "destroy", G_CALLBACK(gtk_main_quit), NULL);

    gtk_container_add(GTK_CONTAINER(window),
            create_tree_view());
    gtk_window_resize(GTK_WINDOW(window),
            800,
            600);

    gtk_widget_show_all(window);
    gtk_main();

    return 0;
}