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Problem This is in response to Manar's post titled "How to disconnect an event?"
He has set up a button-press-event, and he would like to switch the signal handler processing the button-press-event depending on some conditions.
In Part 1 we used the methods connect() and disconnect().
In Part 2 we used the methods block() and unblock().
In this Part 3, instead of using two callback functions, we'll achieve the same effect using just one callback function, with the use of a simple state machine, as shown below:
Solution
- In the situation described by Manar in his post, you can also use just one callback function.
- The variable $state is used to maintain the different state the button is in.
- The advantage of this method is that you do not need to connect/disconnect or block/unblcok the different signals.
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$window = new GtkWindow();
$window->set_size_request(400, 175);
$window->connect_simple('destroy', array('Gtk','main_quit'));
$window->add($vbox = new GtkVBox());
// display title
$title = new GtkLabel("Switching signal handlers on the fly\n".
" Part 3 - using 'state machine'");
$title->modify_font(new PangoFontDescription("Times New Roman Italic 10"));
$title->modify_fg(Gtk::STATE_NORMAL, GdkColor::parse("#0000ff"));
$title->set_size_request(-1, 40);
$vbox->pack_start($title, 0);
$vbox->pack_start(new GtkLabel(), 0);
$label = new GtkLabel('Click on the blue sqaure once. '.
'It will change to green.');
$vbox->pack_start($label, 0);
$state = 1; // note 1
setup_colorbox('#0000ff', 'blue', $vbox);
$window->show_all();
Gtk::main();
function setup_colorbox($color, $label, $vbox) {
$hbox = new GtkHBox();
$hbox->set_size_request(30, 30);
$eventbox = new GtkEventBox();
$eventbox->add($hbox);
$eventbox->modify_bg(Gtk::STATE_NORMAL, GdkColor::parse($color));
$eventbox->connect('button-press-event',
'on_button_press'); // note 2
$hbox = new GtkHBox();
$vbox->pack_start($hbox, 0);
$hbox->pack_start(new GtkLabel());
$hbox->pack_start($eventbox, 0);
$hbox->pack_start(new GtkLabel());
}
function on_button_press($eventbox, $event) {
if ($event->type!=Gdk::BUTTON_PRESS) return false;
global $state;
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- Note that this is only 70% of the sample code. You have to be a registered member to see the entire sample code. Please login or register.
- Registration is free and immediate.
- Have some doubt about the registration? Please read this forum article.
Explanation
- Set the next state of the button to be 1.
- Set up the
button-press-event signal. Note that using this method, we do not need to take note of the signal handler id.
- For state 1, we change the color box from blue to green, and change the state to 2.
- For state 2, we change the color box from green to yellow, and change the state back to 1.
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