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();
  ~ExampleWindow() override;

protected:
  //Signal handlers:
  void on_color_button_color_set();
  void on_button_dialog_clicked();
  void on_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result);

  //Draw function:
  void on_drawing_area_draw(const Cairo::RefPtr<Cairo::Context>& cr, int width, int height);

  //Child widgets:
  Gtk::Box m_VBox;
  Gtk::ColorDialogButton m_ColorDialogButton;
  Gtk::Button m_Button_Dialog;
  Gtk::DrawingArea m_DrawingArea; //To show the color.

  Glib::RefPtr<Gtk::ColorDialog> m_pDialog;
  Gdk::RGBA m_Color;
};

#endif //GTKMM_EXAMPLEWINDOW_H

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

#include "examplewindow.h"
#include <iostream>

ExampleWindow::ExampleWindow()
: m_VBox(Gtk::Orientation::VERTICAL, 5),
  m_Button_Dialog("Choose Color")
{
  set_title("Gtk::ColorDialog example");
  set_default_size(200, 200);

  m_pDialog = Gtk::ColorDialog::create();
  m_ColorDialogButton.set_dialog(m_pDialog);

  set_child(m_VBox);

  m_VBox.append(m_ColorDialogButton);
  m_ColorDialogButton.property_rgba().signal_changed().connect(
    sigc::mem_fun(*this, &ExampleWindow::on_color_button_color_set));

  m_VBox.append(m_Button_Dialog);
  m_Button_Dialog.signal_clicked().connect(sigc::mem_fun(*this,
    &ExampleWindow::on_button_dialog_clicked) );

  //Set start color:
  m_Color.set_red(0.0);
  m_Color.set_green(0.0);
  m_Color.set_blue(1.0);
  m_Color.set_alpha(1.0); //opaque
  m_ColorDialogButton.set_rgba(m_Color);

  m_VBox.append(m_DrawingArea);
  m_DrawingArea.set_expand(true);
  m_DrawingArea.set_draw_func(sigc::mem_fun(*this, &ExampleWindow::on_drawing_area_draw));
}

ExampleWindow::~ExampleWindow()
{
}

void ExampleWindow::on_color_button_color_set()
{
  //Store the chosen color:
  m_Color = m_ColorDialogButton.get_rgba();
  m_DrawingArea.queue_draw();
}

void ExampleWindow::on_button_dialog_clicked()
{
  m_pDialog->choose_rgba(*this, m_Color,
    sigc::mem_fun(*this, &ExampleWindow::on_dialog_finish));
}

void ExampleWindow::on_dialog_finish(const Glib::RefPtr<Gio::AsyncResult>& result)
{
  try
  {
    // If this call changes the color, it will trigger a call to
    // on_color_button_color_set().
    m_ColorDialogButton.set_rgba(m_pDialog->choose_rgba_finish(result));

    // This is what you should do if m_ColorDialogButton and
    // on_color_button_color_set() did not exist:
    //m_Color = m_pDialog->choose_rgba_finish(result);
    //m_DrawingArea.queue_draw();
  }
  catch (const Gtk::DialogError& err)
  {
    // Can be thrown by m_pDialog->choose_rgba_finish(result).
    std::cout << "No color selected. " << err.what() << std::endl;
  }
  catch (const Glib::Error& err)
  {
    std::cout << "Unexpected exception. " << err.what() << std::endl;
  }
}

void ExampleWindow::on_drawing_area_draw(const Cairo::RefPtr<Cairo::Context>& cr, int, int)
{
  Gdk::Cairo::set_source_rgba(cr, m_Color);
  cr->paint();
}

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);
}