GtkGrid is not showing new widgets attached to it

Question

I've decided to make a toy application in which I resize a table of labels by adding rows/cols of elements to GtkGrid.

When adding a new element to the GtkGrid from inside a button callback function, the grid widget updates its size, but fails to update the contents.

#include <gtk/gtk.h>

static void kaboom(GtkWidget*, gpointer);
static void minusVert(GtkWidget*, gpointer);
static void plusVert(GtkWidget*, gpointer);

static int x = 1;
static int y = 1;

int main(int argc, char** argv) {
    GtkWidget* window, *subs, *buts, *grid, *button;

    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "Playground!!");
    gtk_widget_set_size_request(window, 200, 50);

    g_signal_connect(G_OBJECT(window), "destroy", G_CALLBACK(kaboom), NULL);

    subs = gtk_paned_new(GTK_ORIENTATION_VERTICAL);
    gtk_container_add(GTK_CONTAINER(window), subs);

    grid = gtk_grid_new();
    gtk_paned_pack1(GTK_PANED(subs), grid, true, false);

    gtk_grid_set_row_homogeneous(GTK_GRID(grid), true);
    gtk_grid_set_column_homogeneous(GTK_GRID(grid), true);

    gtk_grid_attach(GTK_GRID(grid), gtk_label_new("×"), 0, 0, 1, 1);

    buts = gtk_grid_new();
    gtk_paned_pack2(GTK_PANED(subs), buts, false, false);

    gtk_grid_set_row_homogeneous(GTK_GRID(grid), true);
    gtk_grid_set_column_homogeneous(GTK_GRID(buts), true);

    gtk_grid_attach(GTK_GRID(buts), gtk_label_new("Vertical"), 0, 0, 2, 1);

    button = gtk_button_new_with_label("-");
    g_signal_connect(G_OBJECT(button), "clicked", G_CALLBACK(minusVert), grid);
    gtk_grid_attach(GTK_GRID(buts), button, 0, 1, 1, 1);

    button = gtk_button_new_with_label("+");
    g_signal_connect(G_OBJECT(button), "clicked", G_CALLBACK(plusVert), grid);
    gtk_grid_attach(GTK_GRID(buts), button, 1, 1, 1, 1);

    gtk_grid_attach(GTK_GRID(buts), gtk_label_new("Horizontal"), 2, 0, 2, 1);

    button = gtk_button_new_with_label("-");
    gtk_grid_attach(GTK_GRID(buts), button, 2, 1, 1, 1);

    button = gtk_button_new_with_label("+");
    gtk_grid_attach(GTK_GRID(buts), button, 3, 1, 1, 1);

    gtk_widget_show_all(window);

    gtk_main();

    return 0;
}

static void kaboom(GtkWidget* window, gpointer data) {
    gtk_main_quit();
}

static void minusVert(GtkWidget *button, gpointer data) {
    if (y > 1) {
        // Remove all the elems in the last row
        for (int i = 0; i < x; ++i) {
            gtk_widget_destroy(gtk_grid_get_child_at(GTK_GRID(data), i, y - 1));
        }
        --y;
    }
}

static void plusVert(GtkWidget *button, gpointer data) {
    for (int i = 0; i < x; ++i) {
        // Add the new row
        gtk_grid_attach(GTK_GRID(data), gtk_label_new("×"), i, y, 1, 1);
    }
    ++y;
}

The screenshots before and after:

My question is: how can I make the new labels attached to the GtkGrid visible?

Notes: I'm using C++, but not GTKmm, because I'm working my way through a book written for GTK+. Even if ported to pure C the application behaves the same.

Answer 1

When you create widgets, those are not shown by default. You have to tell them to do so. You can change the callback plusVert for something like:

static void plusVert(GtkWidget *button, gpointer data) {
  for (int i = 0; i < x; ++i) {
    GtkWidget *label = gtk_label_new("×");
    gtk_grid_attach(GTK_GRID(data), label, i, y, 1, 1);
    gtk_widget_show(label);
  }
  ++y;
}

See gtk_widget_show().