Running a function when user stops entering text

Question

I am writing a small GUI application using Haskell's gtk2hs library and am currently working with the multiline text boxes within it. I have a function which I want to run when the user makes changes to the text within the text box, but don't want them to have to click a button to activate it.

Furthermore, because it is a rather intrusive and processing intensive function (It draws graphics, loads files etc.), I would like it to fire not whenever a user makes any change (which could probably be done with the bufferChanged signal in text buffer I'm guessing?) but when they stop for a few seconds in between changes.

Basically I am wondering if there is something in gtk which is analogous to the way range widgets can have their update policy set to continuous or delayed, but for text boxes

Answer 1

I don't know anything of the Haskell bindings but in plain C it is quite easy to implement by leveraging a timeout GSource.

#include <gtk/gtk.h>

static guint source_id = 0;

static gboolean do_stuff(gpointer user_data)
{
    g_print("doing stuff...\n");
    return FALSE;
}

static void postpone(void)
{
    if (source_id > 0)
        g_source_remove(source_id);
    source_id = g_timeout_add(1000, do_stuff, NULL);
}

int main(int argc, char **argv)
{
    GtkWidget *window, *text_view;
    GtkTextBuffer *text_buffer;

    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    g_signal_connect(window, "delete-event", G_CALLBACK(gtk_main_quit), NULL);

    text_view = gtk_text_view_new();
    gtk_container_add(GTK_CONTAINER(window), text_view);

    text_buffer = gtk_text_view_get_buffer(GTK_TEXT_VIEW(text_view));
    g_signal_connect(text_buffer, "changed", G_CALLBACK(postpone), NULL);

    gtk_widget_show_all(window);
    gtk_main();
    return 0;
}

The issue of quitting the TextView before the timeout has elapsed is still open though.