Overview

Whenever you press or release a key, an event is emitted. You can connect a signal handler to handle such events.

The event signal handler will receive an argument that depends on the type of event. For keyboard events it's a GdkEventKey*. As discribed in the appendix, the event signal handler returns a bool value, to indicate that the signal is fully handled (true) or allow event propagation (false).

To determine which key was pressed or released, you read the value of GdkEventKey::keyval and compare it with a constant in the <gdk/gdkkeysyms.h> header file. The states of modifier keys (shift, ctrl, etc.) are available as bit-flags in GdkEventKey::state.

Here's a simple example:

bool on_key_press_or_release_event(GdkEventKey* event)
{
  if (event->type == GDK_KEY_PRESS &&
    event->keyval == GDK_KEY_1 &&
    (event->state & (GDK_SHIFT_MASK | GDK_CONTROL_MASK | GDK_MOD1_MASK)) == GDK_MOD1_MASK)
  {
    handle_alt_1_press(); // GDK_MOD1_MASK is normally the Alt key
    return true;
  }
  return false;
}

Gtk::Entry m_entry; // in a class definition

// in the class constructor
m_entry.signal_key_press_event().connect( sigc::ptr_fun(&on_key_press_or_release_event) );
m_entry.signal_key_release_event().connect( sigc::ptr_fun(&on_key_press_or_release_event) );

21.1.1. Example

In this example there are three keyboard shortcuts: Alt+1 selects the first radio button, Alt+2 selects the second one, and the Esc key hides (closes) the window. The default event signal handler is overridden, as described in the Overriding default signal handlers section in the appendix.

Figure 21-1 Keyboard Events - Simple

Source Code

File: examplewindow.h (For use with gtkmm 4)

#ifndef GTKMM_EXAMPLEWINDOW_H
#define GTKMM_EXAMPLEWINDOW_H

#include <gtkmm.h>

class ExampleWindow : public Gtk::Window
{
public:

  ExampleWindow();
  virtual ~ExampleWindow();

private:
  // Signal handler:
  bool on_window_key_pressed(guint keyval, guint keycode, Gdk::ModifierType state);

  Gtk::Box m_container;
  Gtk::CheckButton m_first;
  Gtk::CheckButton m_second;
};

#endif //GTKMM_EXAMPLEWINDOW_H

File: main.cc (For use with gtkmm 4)

#include "examplewindow.h"
#include <gtkmm/application.h>

int main(int argc, char *argv[])
{
  auto app = Gtk::Application::create("org.gtkmm.example");

  //Shows the window and returns when it is closed.
  return app->make_window_and_run<ExampleWindow>(argc, argv);
}

File: examplewindow.cc (For use with gtkmm 4)

#include "examplewindow.h"

ExampleWindow::ExampleWindow()
{
  set_title("Keyboard Events");
  m_container.set_margin(10);
  set_child(m_container);

  // Radio buttons:
  m_first.set_label("First");
  m_second.set_label("Second");

  m_second.set_group(m_first);
  m_first.set_active();

  // Main Container:
  m_container.set_orientation(Gtk::Orientation::HORIZONTAL);
  m_container.append(m_first);
  m_container.append(m_second);

  // Events.
  auto controller = Gtk::EventControllerKey::create();
  controller->signal_key_pressed().connect(
    sigc::mem_fun(*this, &ExampleWindow::on_window_key_pressed), false);
  add_controller(controller);
}

bool ExampleWindow::on_window_key_pressed(guint keyval, guint, Gdk::ModifierType state)
{
  //Gdk::ModifierType::ALT_MASK -> the 'Alt' key(mask)
  //GDK_KEY_1 -> the '1' key
  //GDK_KEY_2 -> the '2' key

  //select the first radio button, when we press alt + 1
  if((keyval == GDK_KEY_1) &&
    (state & (Gdk::ModifierType::SHIFT_MASK | Gdk::ModifierType::CONTROL_MASK | Gdk::ModifierType::ALT_MASK)) == Gdk::ModifierType::ALT_MASK)
  {
    m_first.set_active();
    //returning true, cancels the propagation of the event
    return true;
  }
  else if((keyval == GDK_KEY_2) &&
    (state & (Gdk::ModifierType::SHIFT_MASK | Gdk::ModifierType::CONTROL_MASK | Gdk::ModifierType::ALT_MASK)) == Gdk::ModifierType::ALT_MASK)
  {
    //and the second radio button, when we press alt + 2
    m_second.set_active();
    return true;
  }
  else if(keyval == GDK_KEY_Escape)
  {
    //close the window, when the 'esc' key is pressed
    hide();
    return true;
  }

  //the event has not been handled
  return false;
}

ExampleWindow::~ExampleWindow()
{
}

Overview

21.1.1. Example

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