Chapter 4. Changes in gtkmm 3

## Chapter 4. Changes in gtkmm 3

gtkmm-3.0 is a new version of the gtkmm API that installs in parallel with the older gtkmm-2.4 API. The last version of the gtkmm-2.4 API was gtkmm 2.24. gtkmm 3 has no major fundamental differences to gtkmm 2 but does make several small changes that were not possible while maintaining binary compatibility. If you never used the gtkmm-2.4 API then you can safely ignore this chapter.

gtkmm 3's library is called `libgtkmm-3.0` rather than `libgtkmm-2.4` and installs its headers in a similarly-versioned directory, so your pkg-config check should ask for `gtkmm-3.0` rather than `gtkmm-2.4`.

gtkmm 3 added some new classes:

1. `Gtk::AppChooser`, `Gtk::AppChooserButton`, `Gtk::AppChooserDialog` allow the user to select an installed application to open a particularl type of content.
2. `Gtk::Grid` is a new container widget that will eventually replace `Gtk::Box`. It arranges its children according to properties of those children rather than its own layout details.
3. `Gtk::Switch` displays On/Off states more explictly than `Gtk::CheckBox`. It may be useful, for instance, when allowing users to activate hardware.

gtkmm 3 also made several small changes to the API, which you will probably encounter when porting code that used gtkmm-2.4. Here is a short list:

1. `Gtk::CellLayout`, used by `Gtk::IconView`, `Gtk::TreeView::Column` and `Gtk::ComboBox`, now has a `Gtk::CellArea` which can be used to specify more details of how the `CellRenderer`s are arranged and aligned.
2. Gtk::ComboBox now derives from CellLayout, allowing easier layout and alignment of its `Gtk::CellRenderer`s.
3. `Gtk::Adjustment` and `IconSet` and `Gdk::Cursor` are now used via `Glib::RefPtr`.
4. `Gtk::Box`, `Gtk::ButtonBox`, `Gtk::IconView`, `Gtk::Paned`, `Gtk::ProgressBar`, `Gtk::ScaleButton`, `Gtk::ScrollBar` and `Gtk::Separator` now derive from `Gtk::Orientable`, allowing their orientation (vertical or horizontal) to be specified without requiring the use of a derived class such as `Gtk::HBox`.
5. `Gtk::IconView`, `Gtk::TextView`, `Gtk::TreeView` and other widgets derive from Scrollable instead of having their own methods such as `get_vadjustment()` and instead of having their won set_scroll_adjustments signal.
6. `Gtk::Style` and `Gtk::Rc` were removed, replaced by `Gtk::StyleContext`, and `Gtk::StyleProvider`s, such as `Gtk::CssProvider`.
7. Widget::on_expose_event() was replaced by Widget::on_draw(), which assumes that cairomm is used for drawing, via the provided `Cairo::Context` and does not require you to call `Cairo::Context::clip()`.
8. `Gdk::RGBA` replaces `Color`, adding an alpha component for opacity. `Colormap` was removed, along with its awkward use to allocate colors.
9. `Gdk::Pixmap` and `Gdk::Bitmap` were removed in favour of `Gdk::Pixbuf`.
10. `Gdk::Drawable` was removed, with its methods moving into `Gdk::Window`.
11. We now use std::vector in several methods instead of the intermediate *Handle types to make the API clearer.

All deprecated API was removed in gtkmm 3.0, though there will be new deprecations in future versions.

As a first step to porting your source code to gtkmm-3.0; you should probably ensure that your application builds with the deprecated gtkmm-2.4; API disabled, by defining macro such as GTK_DISABLE_DEPRECATED. There are some autotools macros that can help with this by defining them optionally at build time. See the gtkmm 3 porting wiki page for more details.

Hello World in gtkmm |  | Chapter 5. Buttons