Example

Here is a very simple example, demonstrating a drag and drop Copy operation:

Figure 17.1. Drag and Drop

Drag and Drop

Source Code

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

#ifndef GTKMM_EXAMPLE_DNDWINDOW_H
#define GTKMM_EXAMPLE_DNDWINDOW_H

#include <gtkmm/box.h>
#include <gtkmm/label.h>
#include <gtkmm/window.h>
#include <gtkmm/button.h>

class DnDWindow : public Gtk::Window
{

public:
  DnDWindow();
  virtual ~DnDWindow();

protected:
  //Signal handlers:
  void on_button_drag_data_get(
          const Glib::RefPtr<Gdk::Drag>& drag,
          Gtk::SelectionData& selection_data);
  void on_label_drop_drag_data_received(
          const Glib::RefPtr<Gdk::Drop>& drop,
          const Gtk::SelectionData& selection_data);

  //Member widgets:
  Gtk::Box m_HBox;
  Gtk::Button m_Button_Drag;
  Gtk::Label m_Label_Drop;
};

#endif // GTKMM_EXAMPLE_DNDWINDOW_H

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

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

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

  DnDWindow dndWindow;

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

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

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

DnDWindow::DnDWindow()
: m_Button_Drag("Drag Here\n"),
  m_Label_Drop("Drop here\n")
{
  set_title("DnD example");

  add(m_HBox);

  //Drag site:

  //Make m_Button_Drag a DnD drag source:
  m_Button_Drag.drag_source_set(Glib::RefPtr<Gdk::ContentFormats>());
  m_Button_Drag.drag_source_add_text_targets();

  //Connect signals:
  m_Button_Drag.signal_drag_data_get().connect(sigc::mem_fun(*this,
              &DnDWindow::on_button_drag_data_get));

  m_HBox.add(m_Button_Drag);
  m_Button_Drag.set_expand(true);

  //Drop site:

  //Make m_Label_Drop a DnD drop destination:
  // Don't do this: m_Label_Drop.drag_dest_set({}).
  // It would call the wrong overload of drag_dest_set() with the wrong
  // default values of flags and actions (wrong in this simple example).
  m_Label_Drop.drag_dest_set(Glib::RefPtr<Gdk::ContentFormats>());
  m_Label_Drop.drag_dest_add_text_targets();

  //Connect signals:
  m_Label_Drop.signal_drag_data_received().connect(sigc::mem_fun(*this,
              &DnDWindow::on_label_drop_drag_data_received) );

  m_HBox.add(m_Label_Drop);
  m_Label_Drop.set_expand(true);
}

DnDWindow::~DnDWindow()
{
}

void DnDWindow::on_button_drag_data_get(
        const Glib::RefPtr<Gdk::Drag>&,
        Gtk::SelectionData& selection_data)
{
  selection_data.set(selection_data.get_target(), 8 /* 8 bits format */,
          (const guchar*)"I'm Data!",
          9 /* the length of I'm Data! in bytes */);
}

void DnDWindow::on_label_drop_drag_data_received(
        const Glib::RefPtr<Gdk::Drop>& drop,
        const Gtk::SelectionData& selection_data)
{
  const int length = selection_data.get_length();
  if((length >= 0) && (selection_data.get_format() == 8))
  {
    std::cout << "Received \"" << selection_data.get_data_as_string()
        << "\" in label " << std::endl;
  }

  drop->failed();
}

There is a more complex example in examples/others/dnd.