Chapter 10. Combo Boxes

## Chapter 10. Combo Boxes

The `ComboBox` widget offers a list (or tree) of choices in a dropdown menu. If appropriate, it can show extra information about each item, such as text, a picture, a checkbox, or a progress bar. The `ComboBox` widget usually restricts the user to the available choices, but it can optionally have an `Entry`, allowing the user to enter arbitrary text if none of the available choices are suitable.

The list is provided via a `TreeModel`, and columns from this model are added to the ComboBox's view with the `ComboBox::pack_start()` method. This provides flexibility and compile-time type-safety, but the `ComboBoxText` class provides a simpler text-based specialization in case that flexibility is not required.

Reference

## The model

The model for a ComboBox can be defined and filled exactly as for a `TreeView`. For instance, you might derive a ComboBox class with one integer and one text column, like so:

    ModelColumns()
    { add(m_col_id); add(m_col_name); }

      Gtk::TreeModelColumn<int> m_col_id;
      Gtk::TreeModelColumn<Glib::ustring> m_col_name;
    };

    ModelColumns m_columns;

After appending rows to this model, you should provide the model to the `ComboBox` with the `set_model()` method. Then use the `pack_start()` or `pack_end()` methods to specify what columns will be displayed in the ComboBox. As with the TreeView you may either use the default cell renderer by passing the `TreeModelColumn` to the pack methods, or you may instantiate a specific `CellRenderer` and specify a particular mapping with either `add_attribute()` or `set_cell_data_func()`. Note that these methods are in the `CellLayout` base class.

Examples |  | The chosen item