Unable to change cursor with GTK3 - c

Question

I am trying to change the cursor of a window dynamically with GTK3 but gtk_widget_get_parent_window doesn't seem to work.
Could someone please point out what I'm doing wrong? Thanks!
// https://developer.gnome.org/gtk3/stable/gtk-getting-started.html
// minimal example
#include <gtk/gtk.h>
static void
activate (GtkApplication* app,
gpointer user_data)
{
GtkWidget *window;
window = gtk_application_window_new (app);
gtk_window_set_title (GTK_WINDOW (window), "Window");
gtk_window_set_default_size (GTK_WINDOW (window), 200, 200);
// Here \/\/\/\/\/ .
GdkWindow* w = gtk_widget_get_parent_window(window);
GdkCursor* c = gdk_cursor_new_for_display(gdk_display_get_default(), GDK_WATCH);
gdk_window_set_cursor(w, c);
// /\/\/\/\/\ .
gtk_widget_show_all (window);
}
int
main (int argc,
char **argv)
{
GtkApplication *app;
int status;
app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
status = g_application_run (G_APPLICATION (app), argc, argv);
g_object_unref (app);
return status;
}
(main.exe:16508): Gdk-CRITICAL **: gdk_window_set_cursor: assertion
'GDK_IS_WINDOW (window)' failed
I am using GTK 3.16 with msys2
Many thanks in advance.

Answer 1

Extending #andlabs comment
Any attempt to change the cursor needs to be done after the widget has been added to the widget hierarchy or in GTK terms realized.
Calling gtk_widget_get_parent_window() or even gtk_widget_get_window() before a realize event has been fired for the widget will result in a NULL pointers in both cases.
Like #andlabs it is safer to use gtk_widget_get_window() in combination with a GtkWindow.
The solution.
static GdkWindow* G_WINDOW = 0;
static GdkCursor* G_CURSOR = 0;
// call after WindowRealize()
void changecursor()
{
assert(G_WINDOW != NULL);
gdk_window_set_cursor(G_WINDOW, G_CURSOR);
}
static void WindowRealize(GtkWidget *window, gpointer data)
{
G_CURSOR_HAND = gdk_cursor_new_for_display(gdk_display_get_default(), GDK_HAND2);
G_WINDOW = gtk_widget_get_window(window);
}
static void activate(GtkApplication* app,gpointer user_data)
{
GtkWidget *window = gtk_application_window_new(app);
...
g_signal_connect(window, "realize", G_CALLBACK(WindowRealize), NULL);
gtk_widget_show_all (window);
}