ask for help: why gtk_grab_get_current returns NULL

[Neo Liu <Neo Liu Sun COM>]

Gurus,

Running below code, the result confused me.

GtkWidget *grabWidget = nsnull;

GetToplevelWidget(&grabWidget);

if (!grabWidget)
       return NS_ERROR_FAILURE;

if (aModal)
 gtk_grab_add(grabWidget);
else
 gtk_grab_remove(grabWidget);

printf("grab widget is %p\n", grabWidget);
printf("current grab widget is %p\n", gtk_grab_get_current());

After gtk_grab_add is executed, gtk_grab_get_current returns NULL. Why?

Thanks in advance and best regards,

ln

p.s. I had sent a same mail before I joined the list. Sorry for post twice.