Multiple-item widgets
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## Multiple-item widgets

Multiple-item widgets inherit from `Gtk::Container`; just as with `Gtk::Bin`, you use the `add()` and `remove()` methods to add and remove contained widgets. Unlike `Gtk::Bin::remove()`, however, the `remove()` method for `Gtk::Container` takes an argument, specifiying which widget to remove.

### Packing

You've probably noticed that gtkmm windows seem "elastic" - they can usually be stretched in many different ways. This is due to the widget packing system.

Many GUI toolkits require you to precisely place widgets in a window, using absolute positioning, often using a visual editor. This leads to several problems:

- The widgets don't rearrange themselves when the window is resized. Some widgets are hidden when the window is made smaller, and lots of useless space appears when the window is made larger.

- It's impossible to predict the amount of space necessary for text after it has been translated to other languages, or displayed in a different font. On Unix it is also impossible to anticipate the effects of every theme and window manager.

- Changing the layout of a window "on the fly", to make some extra widgets appear, for instance, is complex. It requires tedious recalculation of every widget's position.

gtkmm uses the packing system to solve these problems. Rather than specifying the position and size of each widget in the window, you can arrange your widgets in rows, columns, and/or tables. gtkmm can size your window automatically, based on the sizes of the widgets it contains. And the sizes of the widgets are, in turn, determined by the amount of text they contain, or the minimum and maximum sizes that you specify, and/or how you have requested that the available space should be shared between sets of widgets. You can perfect your layout by specifying padding distance and centering values for each of your widgets. gtkmm then uses all this information to resize and reposition everything sensibly and smoothly when the user manipulates the window.

gtkmm arranges widgets hierarchically, using containers. A Container widget contains other widgets. Most gtkmm widgets are containers. Windows, Notebook tabs, and Buttons are all container widgets. There are two flavours of containers: single-child containers, which are all descendants of `Gtk::Bin`, and multiple-child containers, which are descendants of `Gtk::Container`. Most widgets in gtkmm are descendants of `Gtk::Bin`, including `Gtk::Window`.

Yes, that's correct: a Window can contain at most one widget. How, then, can we use a window for anything useful? By placing a multiple-child container in the window. The most useful container widgets are Gtk:VBox, Gtk::HBox, and Gtk::Table:

- `Gtk::VBox` and `Gtk::HBox` arrange their child widgets vertically and horizontally, respectively. Use pack_start() and pack_end() to insert child widgets.

- `Gtk::Table` arranges its widgets in a grid. Use attach() to insert widgets.

There are several other containers, which we will also discuss.

If you've never used a packing toolkit before, it can take some getting used to. You'll probably find, however, that you don't need to rely on visual form editors quite as much as you might with other toolkits.

### An improved Hello World

Let's take a look at a slightly improved `helloworld`, showing what we've learnt.

Figure 7.5. Hello World 2

Source Code

File: helloworld.h

    #ifndef GTKMM_EXAMPLE_HELLOWORLD_H
    #define GTKMM_EXAMPLE_HELLOWORLD_H

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

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

    protected:

      // Signal handlers:
      // Our new improved on_button_clicked(). (see below)
      virtual void on_button_clicked(Glib::ustring data);

      // Child widgets:
      Gtk::HBox m_box1;
      Gtk::Button m_button1, m_button2;
    };

    #endif // GTKMM_EXAMPLE_HELLOWORLD_H

File: helloworld.cc

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

    HelloWorld::HelloWorld()
    : m_button1("Button 1"),
      m_button2("Button 2")
    {
      // This just sets the title of our new window.
      set_title("Hello Buttons!");

      // sets the border width of the window.
      set_border_width(10);

      // put the box into the main window.
      add(m_box1);

      // Now when the button is clicked, we call the "on_button_clicked" function
      // with a pointer to "button 1" as it's argument
      m_button1.signal_clicked().connect(sigc::bind<Glib::ustring>( sigc::mem_fun(*this, &HelloWorld::on_button_clicked), "button 1") );

      // instead of gtk_container_add, we pack this button into the invisible
      // box, which has been packed into the window.
      // note that the pack_start default arguments are Gtk::EXPAND | Gtk::FILL, 0
      m_box1.pack_start(m_button1);

      // always remember this step, this tells GTK that our preparation
      // for this button is complete, and it can be displayed now.
      m_button1.show();

      // call the same signal handler with a different argument,
      // passing a pointer to "button 2" instead.
      m_button2.signal_clicked().connect(sigc::bind<Glib::ustring>( sigc::mem_fun(*this, &HelloWorld::on_button_clicked), "button 2") );

      m_box1.pack_start(m_button2);

      // Show the widgets.
      // They will not really be shown until this Window is shown.
      m_button2.show();
      m_box1.show();
    }

    HelloWorld::~HelloWorld()
    {
    }

    // Our new improved signal handler.  The data passed to this method is
    // printed to stdout.
    void HelloWorld::on_button_clicked(Glib::ustring data)
    {
      std::cout << "Hello World - " << data << " was pressed" << std::endl;
    }

File: main.cc

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

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

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

      return 0;
    }

After building and running this program, try resizing the window to see the behaviour. Also, try playing with the options to `pack_start()` while reading the Boxes section.

### STL-style APIs

TODO: Use 'Standard Library' instead of STL. If you're an accomplished C++ programmer, you'll be happy to hear that most of the gtkmm `Container` widgets provide STL-style APIs, available via accessor methods, such as `Gtk::Box::children()` or `Gtk::Notebook::pages()`. They don't use actual STL containers (there are good reasons for this), but they look, feel, and act much like STL container classes.

These APIs are so similar to STL container APIs that, rather than explaining them in detail, we can refer you to the STL documentation for most of their methods. This is all part of gtkmm's policy of reusing existing standards.

However, STL-style APIs can require awkward or lengthy code in some situations, so some people prefer not to use them, while other people use them religiously. Therefore, you are not forced to use them - most container widgets have a simpler non-STL-style API, with methods such as `append()` and `prepend()`.

At a minimum, gtkmm container lists support iterators and the usual insertion, deletion, and addition methods. You can always expect the following methods to be available for gtkmm STL-style APIs:

- `begin()` returns a `begin` iterator

- `end()` returns an `end` iterator

- `rbegin()` returns a reverse `begin` iterator

- `rend()` returns a reverse `end` iterator

- `size()`

- `max_size()`

- `empty()`

- `insert()`

- `push_front()`

- `push_back()`

- `pop_front()`

- `pop_back()`

- `clear()`

- `erase()`

- `remove()`

- `find()`

- `front()`

- `back()`

Also, the `[]` operator is overloaded, but that is usually order N, so if performance is a consideration, or the list has a large number of elements, think carefully before using it.

The element objects and list objects are defined, for each container, in a namespace whose name ends in `_Helpers`. For example, the helper namespace for the notebook widget is `Gtk::Notebook_Helpers`.

#### Adding items

There is a major difference between gtkmm STL-style APIs and real STL containers. Normally, when you use a `std::vector`, for example, you expect that whatever you put in, you'll get out, unmodified. You wouldn't make a `std::vector<int>` and expect to get `double`s out of it. But, gtkmm STL-style APIs don't always work like that - you will often put one kind of object in, and later get a different kind out. Why this odd behaviour?

Consider a menu widget, which must maintain a hierarchical list of menus and menu items. Menus can only contain certain objects, such as menu items, separators, and submenus. To ensure consistency, a "filter" is needed to keep out illegal objects. Also, since only a few types of objects are allowed, convenience methods can be provided to make it easy to build up menus.

gtkmm takes care of both requirements using special helper elements. Helper elements are temporary - they're typically constructed and passed to an insertion method in the same call. The list insertion method uses the information in the helper element to construct the real object, which is then inserted into the container.

As an example, let's look at the `Notebook` widget (explained in the section on Notebooks). Notebook widgets contain a series of "pages".

Each page in a notebook requires, at minimum, the following information:

- A child widget (zero or one), to be placed in the page

- A label for the page's tab

(The gtkmm notebook widget keeps other data for each page as well.)

To insert a new page in a notebook, we can use one of the notebook helper classes, like this:

    notebook->pages().push_back(
              Gtk::Notebook_Helpers::TabElem(*frame, bufferl));

Let's see what's going on here. Assume we have a pointer to a Notebook widget called `notebook`; we go from that to a member method called `pages()`, which returns an STL-like list object. On this we call the method `push_back()` (this should be familiar to those who know STL).

The object that the `pages()` method returns is called a `Notebook_Helpers::PageList`. It's one of the STL-like containers that we keep referring to. Let's take a look at this class (this has been heavily edited for clarity; see `<gtkmm/notebook.h>` for the actual definition):

    namespace Notebook_Helpers
    {
        class PageList
        {
        public:
                 . . .
            void push_back(const Element& e);
                 . . .
            Page* operator[](size_type l);
        };
    };

There are two important things to notice here:

- The `push_back()` method takes as argument an `Element` object (helper);

- The overloaded `[]` operator returns a pointer to a `Page`.

This scheme has some important advantages:

- We can provide as many different Helper objects as desired, making it simple to construct complex widgets like Menus.

- Construction of the actual objects can be delayed until an appropriate time. Sometimes we don't have enough information until later with GTK+.

- The definitions of the objects contained in the list can change; their interfaces need not concern the programmer. For example, even if the `Page` object changes drastically, the programmer need not be concerned; the `Element`s need not change, and will continue to work as expected.

- New `Element` objects can be added at any time to support new features, without breaking existing code.

All multi-item containers have an `Element` object in their helper namespaces, and usually there are additional classes available (like `TabElem` and `MenuElem`) which derive from `Element`. `Element` classes vary from container to container, since each contains different kinds of objects.

It's very important to remember that `Element`s are not "real" objects. They exist only temporarily, and they are never stored in the container. They are used only as temporary "parameter-holders". Therefore, the following segment of code is illegal:

    MenuElem* m = new MenuElem("hello");
    m->right_justify();
    items().push_back(*m);

We constructed a new `MenuElem` helper object, and then tried to invoke `right_justify()` on it before adding it to the menu. The trouble is that there is no `right_justify()` method in the `MenuElem` class. The correct way to accomplish this would be:

    items().push_back(MenuElem("hello"));
    items().back()->right_justify();

Here, we've constructed a `MenuElem` and inserted it into the menu by passing it to `push_back()`, causing the real menu item to be created. We've then called `right_justify()` on the object retrieved from the list. This is correct - the object retrieved from the list is not a `MenuElem`, but a real `MenuItem`, and therefore supports the `right_justify()` method as expected.

### Boxes

Most packing uses boxes as in the above example. These are invisible containers into which we can pack our widgets. When packing widgets into a horizontal box, the objects are inserted horizontally from left to right or right to left depending on whether `pack_start()` or `pack_end()` is used. In a vertical box, widgets are packed from top to bottom or vice versa. You may use any combination of boxes inside or beside other boxes to create the desired effect.

#### Adding widgets

##### Per-child packing options

The `pack_start()` and `pack_end()` methods place widgets inside these containers. The `pack_start()` method will start at the top and work its way down in a `VBox`, or pack left to right in an `HBox`. `pack_end()` will do the opposite, packing from bottom to top in a `VBox`, or right to left in an `HBox`. Using these methods allows us to right justify or left justify our widgets. We will use `pack_start()` in most of our examples.

There are several options governing how widgets are to be packed, and this can be confusing at first. If you have difficulties then it is sometimes a good idea to play with the `glade` GUI designer to see what is possible. You might even decide to use the `libglademm` API to load your GUI at runtime.

There are basically five different styles, as shown in this picture:

Figure 7.6. Box Packing 1

Each line contains one horizontal box (`HBox`) with several buttons. Each of the buttons on a line is packed into the `HBox` with the same arguments to the `pack_start()` method).

This is the declaration of the `pack_start()` method:

    void pack_start(Gtk::Widget& child, PackOptions options = PACK_EXPAND_WIDGET, guint padding = 0);

The first argument is the widget you're packing. In our example these are all `Buttons`s.

The `options` argument can take one of these three options:

- `PACK_SHRINK`: Space is contracted to the child widget size. The widget will take up just-enough space and never expand.

- `PACK_EXPAND_PADDING`: Extra space is filled with padding. The widgets will be spaced out evenly, but their sizes won't change - there will be empty space between the widgets instead.

- `PACK_EXPAND_WIDGET`: Extra space is taken up by increasing the child widget size, without changing the amount of space between widgets.

The `padding` argument specifies the width of an extra border area to leave around the packed widget.

Instead of the `pack_start()` and `pack_end()` methods, you might prefer to use the STL-style API, available via the `children` method. See the STL-style APIs section for more details.

Reference

##### Per-container packing options

Here's the constructor for the box widgets:

    Gtk::Box(bool homogeneous = false, int spacing = 0);

Passing `true` for `homogeneous` will cause all of the contained widgets to be the same size. `spacing` is a (minimum) number of pixels to leave between each widget.

What's the difference between spacing (set when the box is created) and padding (set when elements are packed)? Spacing is added between objects, and padding is added on either side of a widget. The following figure should make it clearer:

Figure 7.7. Box Packing 2

#### Example

Here is the source code for the example that produced the screenshots above. When you run this example, provide a number between 1 and 3 as a command-line option, to see different packing options in use.

Source Code

File: examplewindow.h

    #ifndef GTKMM_EXAMPLEWINDOW_H
    #define GTKMM_EXAMPLEWINDOW_H

    #include <gtkmm.h>
    #include <packbox.h>

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

    protected:
      //Signal handlers:
      virtual void on_button_quit_clicked();

      //Child widgets:
      Gtk::Button m_button;
      Gtk::VBox m_box1;
      Gtk::HBox m_boxQuit;
      Gtk::Button m_buttonQuit;

      Gtk::Label m_Label1, m_Label2;

      Gtk::HSeparator m_seperator1, m_seperator2, m_seperator3, m_seperator4, m_seperator5;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: packbox.h

    #ifndef GTKMM_EXAMPLE_PACKBOX_H
    #define GTKMM_EXAMPLE_PACKBOX_H

    #include <gtkmm.h>

    class PackBox : public Gtk::HBox
    {
    public:
      PackBox(bool homogeneous, int spacing, Gtk::PackOptions, int padding = 0);
      virtual ~PackBox();

    protected:
      Gtk::Button m_button1, m_button2, m_button3;
      Gtk::Button* m_pbutton4;

      char padstr[80];
    };

    #endif //GTKMM_EXAMPLE_PACKBOX_H

File: examplewindow.cc

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

    ExampleWindow::ExampleWindow(int which)
    : m_buttonQuit("Quit")
    {
      set_title("Gtk::Box example");

      PackBox *pPackBox1, *pPackBox2, *pPackBox3, *pPackBox4, *pPackBox5;

      switch(which)
      {
        case 1:
        {
          m_Label1.set_text("Gtk::HBox(false, 0);");

          // Align the label to the left side.  We'll discuss this function and
          // others in the section on Widget Attributes.
          m_Label1.set_alignment(Gtk::ALIGN_LEFT, Gtk::ALIGN_TOP);

          // Pack the label into the vertical box (vbox box1).  Remember that
          // widgets added to a vbox will be packed one on top of the other in
          // order.
          m_box1.pack_start(m_Label1, Gtk::PACK_SHRINK);

          // Create a PackBox - homogeneous = false, spacing = 0,
          // options = Gtk::PACK_SHRINK, padding = 0
          pPackBox1 = Gtk::manage(new PackBox(false, 0, Gtk::PACK_SHRINK));
          m_box1.pack_start(*pPackBox1, Gtk::PACK_SHRINK);

          // Create a PackBox - homogeneous = false, spacing = 0,
          // options = Gtk::PACK_EXPAND_PADDING, padding = 0
          pPackBox2 = Gtk::manage(new PackBox(false, 0, Gtk::PACK_EXPAND_PADDING));
          m_box1.pack_start(*pPackBox2, Gtk::PACK_SHRINK);

          // Create a PackBox - homogeneous = false, spacing = 0,
          // options = Gtk::PACK_EXPAND_WIDGET, padding = 0
          pPackBox3 = Gtk::manage(new PackBox(false, 0, Gtk::PACK_EXPAND_WIDGET));
          m_box1.pack_start(*pPackBox3, Gtk::PACK_SHRINK);

          // pack the separator into the vbox.  Remember each of these
          // widgets are being packed into a vbox, so they'll be stacked
          // vertically.
          m_box1.pack_start(m_seperator1, Gtk::PACK_SHRINK, 5);

          // create another new label, and show it.
          m_Label2.set_text("Gtk::HBox(true, 0);");
          m_Label2.set_alignment(Gtk::ALIGN_LEFT, Gtk::ALIGN_TOP);
          m_box1.pack_start(m_Label2, Gtk::PACK_SHRINK);

          // Args are: homogeneous, spacing, options, padding
          pPackBox4 = Gtk::manage(new PackBox(true, 0, Gtk::PACK_EXPAND_PADDING));
          m_box1.pack_start(*pPackBox4, Gtk::PACK_SHRINK);

          // Args are: homogeneous, spacing, options, padding
          pPackBox5 = Gtk::manage(new PackBox(true, 0, Gtk::PACK_EXPAND_WIDGET));
          m_box1.pack_start(*pPackBox5, Gtk::PACK_SHRINK);

          m_box1.pack_start(m_seperator2, Gtk::PACK_SHRINK, 5);

          break;
        }

        case 2:
        {

          m_Label1.set_text("Gtk::HBox(false, 10);");
          m_Label1.set_alignment(Gtk::ALIGN_LEFT, Gtk::ALIGN_TOP);
          m_box1.pack_start(m_Label1, Gtk::PACK_SHRINK);

          pPackBox1 = Gtk::manage(new PackBox(false, 10, Gtk::PACK_EXPAND_PADDING));
          m_box1.pack_start(*pPackBox1, Gtk::PACK_SHRINK);

          pPackBox2 = Gtk::manage(new PackBox(false, 10, Gtk::PACK_EXPAND_WIDGET));
          m_box1.pack_start(*pPackBox2, Gtk::PACK_SHRINK);

          m_box1.pack_start(m_seperator1, Gtk::PACK_SHRINK, 5);

          m_Label2.set_text("Gtk::HBox(false, 0);");
          m_Label2.set_alignment(Gtk::ALIGN_LEFT, Gtk::ALIGN_TOP);
          m_box1.pack_start(m_Label2, Gtk::PACK_SHRINK);

          pPackBox3 = Gtk::manage(new PackBox(false, 0, Gtk::PACK_SHRINK, 10));
          m_box1.pack_start(*pPackBox3, Gtk::PACK_SHRINK);

          pPackBox4 = Gtk::manage(new PackBox(false, 0, Gtk::PACK_EXPAND_WIDGET, 10));
          m_box1.pack_start(*pPackBox4, Gtk::PACK_SHRINK);

          m_box1.pack_start(m_seperator2, Gtk::PACK_SHRINK, 5);

          break;
        }

        case 3:
        {
          // This demonstrates the ability to use Gtk::Box::pack_end() to
          // right justify widgets.  First, we create a new box as before.
          pPackBox1 = Gtk::manage(new PackBox(false, 0, Gtk::PACK_SHRINK));

          // create the label that will be put at the end.
          m_Label1.set_text("end");

          // pack it using pack_end(), so it is put on the right side
          // of the PackBox.
          pPackBox1->pack_end(m_Label1, Gtk::PACK_SHRINK);

          m_box1.pack_start(*pPackBox1, Gtk::PACK_SHRINK);

          // this explicitly sets the separator to 400 pixels wide by 5 pixels
          // high.  This is so the hbox we created will also be 400 pixels wide,
          // and the "end" label will be separated from the other labels in the
          // hbox.  Otherwise, all the widgets in the hbox would be packed as
          // close together as possible.
          m_seperator1.set_size_request(400, 5);

          // pack the separator into ourselves
          m_box1.pack_start(m_seperator1, Gtk::PACK_SHRINK, 5);

          break;
        }

        default:
        {
          std::cerr << "Unexpected command-line option." << std::endl;
          break;
        }
      }

      // Connect the signal to hide the window:
      m_buttonQuit.signal_clicked().connect( sigc::mem_fun(*this, &ExampleWindow::on_button_quit_clicked) );

      // pack the button into the quitbox.
      // The last 2 arguments to Box::pack_start are: options, padding.
      m_boxQuit.pack_start(m_buttonQuit, Gtk::PACK_EXPAND_PADDING);
      m_box1.pack_start(m_boxQuit, Gtk::PACK_SHRINK);

      // pack the vbox (box1) which now contains all our widgets, into the
      // main window.
      add(m_box1);

      show_all_children();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit_clicked()
    {
      hide();
    }

File: main.cc

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

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

      if(argc != 2)
      {
        std::cerr << "usage: packbox num, where num is 1, 2, or 3." << std::endl;
        // this just does cleanup in GTK, and exits with an exit status of 1.
        gtk_exit (1);
      }

      ExampleWindow window( atoi(argv[1]) );
      Gtk::Main::run(window); //Shows the window and returns when it is closed.

      return 0;
    }

File: packbox.cc

    #include "packbox.h"
    #include <cstdio> //For sprintf().

    PackBox::PackBox(bool homogeneous, int spacing, Gtk::PackOptions options, int padding) :
      Gtk::HBox(homogeneous, spacing),
      m_button1("box.pack_start("),
      m_button2("button,"),
      m_button3((options == Gtk::PACK_SHRINK) ? "Gtk::PACK_SHRINK" :
                ((options == Gtk::PACK_EXPAND_PADDING) ? "Gtk::PACK_EXPAND_PADDING" : "Gtk::PACK_EXPAND_WIDGET"))
    {
      pack_start(m_button1, options, padding);
      pack_start(m_button2, options, padding);
      pack_start(m_button3, options, padding);

      sprintf(padstr, "%d);", padding);

      m_pbutton4 = new Gtk::Button(padstr);
      pack_start(*m_pbutton4, options, padding);
    }

    PackBox::~PackBox()
    {
      delete m_pbutton4;
    }

### ButtonBoxes

Button boxes are a convenient way to quickly arrange a group of buttons. They come in both horizontal (`Gtk::HButtonBox`) and vertical (`Gtk::VButtonBox`) flavours. They are exactly alike, except in name and orientation.

ButtonBoxes help to make applications appear consistent because they use standard settings, such as inter-button spacing and packing.

Buttons are added to a `ButtonBox` with the `add()` method.

Button boxes support several layout styles. The style can be retrieved and changed using `get_layout()` and `set_layout()`.

Reference

#### Example

Figure 7.8. ButtonBox

Source Code

File: examplebuttonbox.h

    #ifndef GTKMM_EXAMPLE_BUTTONBOX_H
    #define GTKMM_EXAMPLE_BUTTONBOX_H

    #include <gtkmm.h>

    class ExampleButtonBox : public Gtk::Frame
    {
    public:
      ExampleButtonBox(bool horizontal,
           const Glib::ustring& title,
           gint spacing,
           Gtk::ButtonBoxStyle layout);

    protected:
      Gtk::Button m_Button_OK, m_Button_Cancel, m_Button_Help;
    };

    #endif //GTKMM_EXAMPLE_BUTTONBOX_H

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 void on_button_clicked();

      //Child widgets:
      Gtk::VBox m_VBox_Main, m_VBox;
      Gtk::HBox m_HBox;
      Gtk::Frame m_Frame_Horizontal, m_Frame_Vertical;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: examplebuttonbox.cc

    #include "examplebuttonbox.h"

    ExampleButtonBox::ExampleButtonBox(bool horizontal,
           const Glib::ustring& title,
           gint spacing,
           Gtk::ButtonBoxStyle layout)
    : Gtk::Frame(title),
      m_Button_OK("OK"),
      m_Button_Cancel("Cancel"),
      m_Button_Help("Help")
    {
      Gtk::ButtonBox* bbox = 0;

      if(horizontal)
        bbox = Gtk::manage( new Gtk::HButtonBox() );
      else
        bbox = Gtk::manage( new Gtk::VButtonBox() );

      bbox->set_border_width(5);

      add(*bbox);

      /* Set the appearance of the Button Box */
      bbox->set_layout(layout);
      bbox->set_spacing(spacing);

      bbox->add(m_Button_OK);
      bbox->add(m_Button_Cancel);
      bbox->add(m_Button_Help);
    }

File: examplewindow.cc

    #include "examplewindow.h"
    #include "examplebuttonbox.h"

    ExampleWindow::ExampleWindow()
    : m_Frame_Horizontal("Horizontal Button Boxes"),
      m_Frame_Vertical("Vertical Button Boxes")
    {
      set_title("Gtk::ButtonBox");
      add(m_VBox_Main);

      m_VBox_Main.pack_start(m_Frame_Horizontal, Gtk::PACK_EXPAND_WIDGET, 10);

      //The horizontal ButtonBoxes:
      m_VBox.set_border_width(10);
      m_Frame_Horizontal.add(m_VBox);

      m_VBox.pack_start( *Gtk::manage( new ExampleButtonBox(true, "Spread (spacing 40)",
                                          40, Gtk::BUTTONBOX_SPREAD)),
         Gtk::PACK_EXPAND_WIDGET, 0);

      m_VBox.pack_start( *Gtk::manage( new ExampleButtonBox(true, "Edge (spacing 30)",
                                    30, Gtk::BUTTONBOX_EDGE)),
         Gtk::PACK_EXPAND_WIDGET, 5);

      m_VBox.pack_start( *Gtk::manage( new ExampleButtonBox(true, "Start (spacing 20)",
                                          20, Gtk::BUTTONBOX_START)),
         Gtk::PACK_EXPAND_WIDGET, 5);

      m_VBox.pack_start( *Gtk::manage( new ExampleButtonBox(true, "end (spacing 10)",
                                          10, Gtk::BUTTONBOX_END)),
         Gtk::PACK_EXPAND_WIDGET, 5);

      //The vertical ButtonBoxes:
      m_VBox_Main.pack_start(m_Frame_Vertical, Gtk::PACK_EXPAND_WIDGET, 10);

      m_HBox.set_border_width(10);
      m_Frame_Vertical.add(m_HBox);

      m_HBox.pack_start( *Gtk::manage( new ExampleButtonBox(false, "Spread (spacing 5)",
                                          5, Gtk::BUTTONBOX_SPREAD)),
          Gtk::PACK_EXPAND_WIDGET, 0);

      m_HBox.pack_start( *Gtk::manage( new ExampleButtonBox(false, "Edge (spacing 30)",
                                         30, Gtk::BUTTONBOX_EDGE)),
          Gtk::PACK_EXPAND_WIDGET, 5);

      m_HBox.pack_start( *Gtk::manage( new ExampleButtonBox(false, "Start (spacing 20)",
                                          20, Gtk::BUTTONBOX_START)),
          Gtk::PACK_EXPAND_WIDGET, 5);

      m_HBox.pack_start( *Gtk::manage( new ExampleButtonBox(false, "End (spacing 10)",
                                          10, Gtk::BUTTONBOX_END)),
          Gtk::PACK_EXPAND_WIDGET, 5);

      show_all_children();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_clicked()
    {
      hide();
    }

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;
    }

### Table

Tables allows us to place widgets in a grid.

#### Constructor

The grid's dimensions need to be specified in the constructor:

    Gtk::Table(int rows = 1, int columns = 1, bool homogeneous = false);

The first argument is the number of rows to make in the table, while the second, obviously, is the number of columns. If `homogeneous` is `true`, the table cells will all be the same size (the size of the largest widget in the table).

The rows and columns are indexed starting at 0. If you specify `rows` = 2 and `columns` = 2, the layout would look something like this:

     0          1          2
    0+----------+----------+
     |          |          |
    1+----------+----------+
     |          |          |
    2+----------+----------+

Note that the coordinate system starts in the upper left hand corner.

#### Adding widgets

To place a widget into a box, use the following method:

    void Gtk::Table::attach(Gtk::Widget& child,
                            guint left_attach, guint right_attach,
                            guint top_attach, guint bottom_attach,
                            guint xoptions = Gtk::FILL | Gtk::EXPAND,
                            guint yoptions = Gtk::FILL | Gtk::EXPAND,
                            guint xpadding = 0, guint ypadding = 0);

The first argument is the widget you wish to place in the table.

The `left_attach` and `right_attach` arguments specify where to place the widget, and how many boxes to use. For example, if you want a button in the lower-right cell of a 2 x 2 table, and want it to occupy that cell only, then `left_attach` would be 1, `right_attach` 2, `top_attach` 1, and `bottom_attach` 2. If, on the other hand, you wanted a widget to take up the entire top row of our 2 x 2 table, you'd set `left_attach` = 0, `right_attach` = 2, `top_attach` = 0, and `bottom_attach` = 1.

`xoptions` and `yoptions` are used to specify packing options and may be bitwise ORed together to allow multiple options. These options are:

`Gtk::FILL`

  If the table box is larger than the widget, and `Gtk::FILL` is specified, the widget will expand to use all the room available.

`Gtk::SHRINK`

  If the table widget is allocated less space than it requested (because the user resized the window), then the widgets will normally just disappear off the bottom of the window. If `Gtk::SHRINK` is specified, the widgets will shrink with the table.

`Gtk::EXPAND`

  This will cause the table to expand to use up anyremaining space in the window.

The padding arguments work just as they do for `pack_start()`.

#### Other methods

`set_row_spacing()` and `set_col_spacing()` set the spacing between the rows at the specified row or column. Note that for columns, the space goes to the right of the column, and for rows, the space goes below the row.

You can also set a consistent spacing for all rows and/or columns with `set_row_spacings()` and `set_col_spacings()`. Note that with these calls, the last row and last column do not get any spacing.

Reference

#### Example

In the following example, we make a window with three buttons in a 2 x 2 table. The first two buttons will be placed in the upper row. A third button is placed in the lower row, spanning both columns.

Figure 7.9. Table

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 void on_button_quit();
      virtual void on_button_numbered(Glib::ustring data);

      //Child widgets:
      Gtk::Table m_Table;
      Gtk::Button m_Button_1, m_Button_2, m_Button_Quit;

    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: examplewindow.cc

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

    ExampleWindow::ExampleWindow()
    : m_Table(2, 2, true),
      m_Button_1("button 1"),
      m_Button_2("button 2"),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::Table");
      set_border_width(20);

      add(m_Table);

      m_Table.attach(m_Button_1, 0, 1, 0, 1);
      m_Table.attach(m_Button_2, 1, 2, 0, 1);
      m_Table.attach(m_Button_Quit, 0, 2, 1, 2);

      m_Button_1.signal_clicked().connect(
          sigc::bind<Glib::ustring>( sigc::mem_fun(*this, &ExampleWindow::on_button_numbered), "button 1") );
      m_Button_2.signal_clicked().connect(
          sigc::bind<Glib::ustring>( sigc::mem_fun(*this, &ExampleWindow::on_button_numbered), "button 2") );

      m_Button_Quit.signal_clicked().connect( sigc::mem_fun(*this, &ExampleWindow::on_button_quit) );

      show_all_children();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      hide();
    }

    void
    ExampleWindow::on_button_numbered(Glib::ustring data)
    {
      std::cout << "Hello again - " << data << " was pressed" << std::endl;
    }

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;
    }

### Notebook

A `Notebook` has a set of stacked `pages`, each of which contains widgets. Labelled `tabs` allow the user to select the pages. `Notebooks` allow several sets of widgets to be placed in a small space, by only showing one page at a time. For instance, they are often used in preferences dialogs.

Use the `append_page()`, `prepend_page()` and `insert_page()` methods to add tabbed pages to the `Notebook`, supplying the child widget and the name for the tab.

To discover the currently visible page, use the `get_current_page()` method. This returns the page number, and then calling `get_nth_page()` with that number will give you a pointer to the actual child widget.

To programmatically change the selected page, use the `set_page()` method.

There is also an STL-style API which you might find more obvious.

Reference

#### Example

Figure 7.10. Notebook

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 void on_button_quit();

      //Child widgets:
      Gtk::VBox m_VBox;
      Gtk::Notebook m_Notebook;
      Gtk::Label m_Label1, m_Label2;

      Gtk::HButtonBox m_ButtonBox;
      Gtk::Button m_Button_Quit;
    };

    #endif //GTKMM_EXAMPLEWINDOW_H

File: examplewindow.cc

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

    ExampleWindow::ExampleWindow()
    : m_Label1("Contents of tab 1"),
      m_Label2("Contents of tab 2"),
      m_Button_Quit("Quit")
    {
      set_title("Gtk::Notebook example");
      set_border_width(10);
      set_default_size(400, 200);

      add(m_VBox);

      //Add the Notebook, with the button underneath:
      m_Notebook.set_border_width(10);
      m_VBox.pack_start(m_Notebook);
      m_VBox.pack_start(m_ButtonBox, Gtk::PACK_SHRINK);

      m_ButtonBox.pack_start(m_Button_Quit, Gtk::PACK_SHRINK);
      m_Button_Quit.signal_clicked().connect( sigc::mem_fun(*this, &ExampleWindow::on_button_quit) );

      //Add the Notebook pages:
      m_Notebook.append_page(m_Label1, "First");
      m_Notebook.append_page(m_Label2, "Second");

      show_all_children();
    }

    ExampleWindow::~ExampleWindow()
    {
    }

    void ExampleWindow::on_button_quit()
    {
      hide();
    }

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;
    }

#### STL-style API

The `Gtk::Notebook` widget has an STL-style API, available via the `pages()` method, which you might prefer to use to add and access pages. See the STL-style APIs section for generic information.

PageList Reference

To insert pages into a notebook, use the `TabElem` helper class, like so:

    m_Notebook.pages().push_back( Gtk::Notebook_Helpers::TabElem(m_ChildWidget, "tab 1") );

TabElem Reference. TODO: Correct URL.

To access an existing child widget, you can call `get_child()` on one of the `Page` elements of the `PageList`:

    Gtk::Widget* pWidget = m_Notebook.pages()[2].get_child();

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