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<tr><th colspan="3" align="center">Example</th></tr>
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<th width="60%" align="center">Chapter 19. Drag and Drop</th>
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sec-dnd-example"></a>Example</h2></div></div></div>
<p>Here is a very simple example, demonstrating a drag and drop <code class="literal">Copy</code> operation:</p>
<div class="figure">
<a name="figure-drag-and-drop"></a><p class="title"><b>Figure 19.1. Drag and Drop</b></p>
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<div class="mediaobject"><img src="figures/drag_and_drop.png" alt="Drag and Drop"></div>
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<p><a class="ulink" href="https://gitlab.gnome.org/GNOME/gtkmm-documentation/tree/master/examples/book/drag_and_drop" target="_top">Source Code</a></p>
<p>File: <code class="filename">dndwindow.h</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#ifndef GTKMM_EXAMPLE_DNDWINDOW_H
#define GTKMM_EXAMPLE_DNDWINDOW_H
#include <gdkmm/drop.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:
Glib::RefPtr<Gdk::ContentProvider> on_label_drag_prepare_data(double x, double y);
bool on_button_drop_drop_data(const Glib::ValueBase& value, double x, double y);
//Member widgets:
Gtk::Box m_HBox;
Gtk::Label m_Label_Drag;
Gtk::Button m_Button_Drop;
};
#endif // GTKMM_EXAMPLE_DNDWINDOW_H
</code></pre>
<p>File: <code class="filename">dndwindow.cc</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#include "dndwindow.h"
#include <gdkmm/contentprovider.h>
#include <gtkmm/dragsource.h>
#include <gtkmm/droptarget.h>
#include <iostream>
DnDWindow::DnDWindow()
: m_Label_Drag("Drag Here\n"),
m_Button_Drop("Drop here\n")
{
set_title("DnD example");
set_child(m_HBox);
//Drag site:
//Make m_Label_Drag a DnD drag source:
auto source = Gtk::DragSource::create();
source->set_actions(Gdk::DragAction::COPY);
source->signal_prepare().connect(
sigc::mem_fun(*this, &DnDWindow::on_label_drag_prepare_data), false);
m_Label_Drag.add_controller(source);
m_HBox.append(m_Label_Drag);
m_Label_Drag.set_expand(true);
//Drop site:
//Make m_Button_Drop a DnD drop destination:
const GType ustring_type = Glib::Value<Glib::ustring>::value_type();
auto target = Gtk::DropTarget::create(ustring_type, Gdk::DragAction::COPY);
target->signal_drop().connect(
sigc::mem_fun(*this, &DnDWindow::on_button_drop_drop_data), false);
m_Button_Drop.add_controller(target);
m_HBox.append(m_Button_Drop);
m_Button_Drop.set_expand(true);
}
DnDWindow::~DnDWindow()
{
}
// In this simple example where just a small amount of data is copied,
// it would be reasonable to store the ContentProvider in the DragSource.
// Then this signal handler would be unnecessary.
Glib::RefPtr<Gdk::ContentProvider> DnDWindow::on_label_drag_prepare_data(double, double)
{
Glib::Value<Glib::ustring> ustring_value;
ustring_value.init(ustring_value.value_type());
ustring_value.set("I'm Data!");
return Gdk::ContentProvider::create(ustring_value);
}
bool DnDWindow::on_button_drop_drop_data(const Glib::ValueBase& value, double, double)
{
if (G_VALUE_HOLDS(value.gobj(), Glib::Value<Glib::ustring>::value_type()))
{
// We got the value type that we expected.
Glib::Value<Glib::ustring> ustring_value;
ustring_value.init(value.gobj());
const Glib::ustring dropped_string = ustring_value.get();
std::cout << "Received \"" << dropped_string << "\" in button " << std::endl;
return true;
}
else
{
std::cout << "Received unexpected data type \""
<< G_VALUE_TYPE_NAME(value.gobj()) << "\" in button " << std::endl;
return false;
}
}
</code></pre>
<p>File: <code class="filename">main.cc</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#include "dndwindow.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<DnDWindow>(argc, argv);
}
</code></pre>
<p>
There is a more complex example in examples/others/dnd.
</p>
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