Chapter 12. Widgets Without X-Windows

## Chapter 12. Widgets Without X-Windows

Some Widgets do not have an associated X-Window, so they therefore do not receive X events. This means that the signals described in the X event signals section will not be emitted. If you want to capture events for these widgets you can use a special container called `Gtk::EventBox`, which is described in the EventBox section.

Here is a list of some of these Widgets:

    Gtk::Alignment
    Gtk::Arrow
    Gtk::Bin
    Gtk::Box
    Gtk::Image
    Gtk::Item
    Gtk::Label
    Gtk::Pixmap
    Gtk::ScrolledWindow
    Gtk::Separator
    Gtk::Table
    Gtk::AspectFrame
    Gtk::Frame
    Gtk::VBox
    Gtk::HBox
    Gtk::VSeparator
    Gtk::HSeparator

These widgets are mainly used for decoration or layout, so you won't often need to capture events on them. They are intended to have no X-Window in order to improve performance.

## EventBox

TODO: Why don't they have X Windows - explain clipping. Some gtkmm widgets don't have associated X windows; they draw on their parents' windows. Because of this, they cannot receive events. Also, if they are incorrectly sized, they don't clip, so you can get messy overwriting etc. If you require more from these widgets, the EventBox is for you. Although the name EventBox emphasises the event-handling method, the widget can also be used for clipping (and more; see the example below).

The constructor for `Gtk::EventBox` is:

    Gtk::EventBox();

A child widget can be added to the EventBox using:

    event_box.add(child_widget);

Reference

### Example

The following example demonstrates both uses of an `EventBox` - a label is created that is clipped to a small box, and set up so that a mouse-click on the label causes the program to exit. Resizing the window reveals varying amounts of the label.

Figure 12.1. EventBox

Source Code

File: `examplewindow.h`

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>

    class ExampleWindow : public Gtk::Window
    {
    public:
      ExampleWindow();
      virtual ~ExampleWindow();

    protected:
      //Signal handlers:
      virtual bool on_eventbox_button_press(GdkEventButton* event);

      //Child widgets:
      Gtk::EventBox m_EventBox;
      Gtk::Label m_Label;
      Gtk::Tooltips m_Tooltips;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: `examplewindow.cc`

    #include "examplewindow.h"

    ExampleWindow::ExampleWindow()
    : m_Label("Click here to quit, quit, quit, quit, quit")
    {
      set_title ("EventBox");
      set_border_width(10);

      add(m_EventBox);

      m_EventBox.add(m_Label);

      //Clip the label short:
      m_Label.set_size_request(110, 20);

      //And bind an action to it:
      m_EventBox.set_events(Gdk::BUTTON_PRESS_MASK);
      m_EventBox.signal_button_press_event().connect(
        sigc::mem_fun(*this, &ExampleWindow::on_eventbox_button_press) );

      m_Tooltips.set_tip(m_EventBox, "Click me!");

      show_all_children();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    bool ExampleWindow::on_eventbox_button_press(GdkEventButton*)
    {
      hide();
      return true;
    }

File: `main.cc`

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

    int main(int argc, char *argv[])
    {
      Gtk::Main kit(argc, argv);

      ExampleWindow window;
      Gtk::Main::run(window); //Shows the window and returns when it is closed.

      return 0;
    }

Adjustment Internals |  | Chapter 13. Dialogs