Table of Contents
All container widgets derive from Gtk::Container, not always directly. Some container widgets, such as Gtk::Table can hold many child widgets, so these typically have more complex interfaces. Others, such as Gtk::Frame contain only one child widget.
The single-item container widgets derive from Gtk::Bin, which provides the add() and remove() methods for the child widget. Note that Gtk::Button and Gtk::Window are technically single-item containers, but we have discussed them already elsewhere.
We also discuss the Gtk::Paned widget, which allows you to divide a window into two separate "panes". This widget actually contains two child widgets, but the number is fixed so it seems appropriate.
Frames can enclose one or a group of widgets within a box, optionally with a title. For instance, you might place a group of RadioButtons or CheckButtons in a Frame.
Panes divide a widget into two halves, separated by a moveable divider. There are two such widgets: Gtk::HPaned adds a horizontal divider, and Gtk::VPaned adds a vertical one. Other than the names and the orientations, there's no difference between the two.
Unlike the other widgets in this chapter, pane widgets contain not one but two child widgets, one in each pane. Therefore, you should use add1() and add2() instead of the add() method.
You can adjust the position of the divider using the set_position() method, and you will probably need to do so.
ScrolledWindow widgets are used to create a scrollable area. You can insert any type of widget into a ScrolledWindow window, and it will be accessible regardless of its size by using the scrollbars. Note that ScrolledWindow is not a Gtk::Window despite the slightly misleading name.
Scrolled windows have scrollbar policies which determine whether the Scrollbars will be displayed. The policies can be set with the set_policy() method. The policy may be one of Gtk::POLICY_AUTOMATIC or Gtk::POLICY_ALWAYS. Gtk::POLICY_AUTOMATIC will cause the scrolled window to display the scrollbar only if the contained widget is larger than the visible area. Gtk::POLICY_ALWAYS will cause the scrollbar to be displayed always.
Here is a simple example that packs 100 toggle buttons into a ScrolledWindow. Try resizing the window to see the scrollbars react.
The AspectFrame widget looks like a Frame widget, but it also enforces the aspect ratio (the ratio of the width to the height) of the child widget, adding extra space if necessary. For instance, this would allow you to display a photograph without allowing the user to distort it horizontally or vertically while resizing.
The Alignment widget allows you to place a widget at a position and size relative to the size of the Alignment widget itself. For instance, it might be used to center a widget.
You need to specify the Alignment's characteristics to the constructor, or to the set() method. In particular, you won't notice much effect unless you specify a number other than 1.0 for the xscale and yscale parameters, because 1.0 simply means that the child widget will expand to fill all available space.
This example right-aligns a button in a window by using an Alignment widget.
See the ProgressBar section for another example that uses an Alignment.