# Source code for enaml.widgets.combo_box

    #------------------------------------------------------------------------------
    # Copyright (c) 2013-2025, Nucleic Development Team.
    #
    # Distributed under the terms of the Modified BSD License.
    #
    # The full license is in the file LICENSE, distributed with this software.
    #------------------------------------------------------------------------------
    from atom.api import (
        Bool, List, Int, Property, Str, Typed, ForwardTyped, set_default
    )

    from enaml.core.declarative import d_, observe

    from .control import Control, ProxyControl

    class ProxyComboBox(ProxyControl):
        """ The abstract definition of a proxy ComboBox object.

        """
        #: A reference to the ComboBox declaration.
        declaration = ForwardTyped(lambda: ComboBox)

        def set_items(self, items):
            raise NotImplementedError

        def set_index(self, index):
            raise NotImplementedError

        def set_editable(self, editable):
            raise NotImplementedError

    class ComboBox(Control):
        """ A drop-down list from which one item can be selected at a time.

        Use a combo box to select a single item from a collection of items.

        See `ObjectCombo` for a more robust combo box control.

        """
        #: The strings to display in the combo box.
        items = d_(List(Str()))

        #: The integer index of the currently selected item. If the index
        #: falls outside the range of items, the item will be deselected.
        index = d_(Int(-1))

        #: A read only cached property which returns the selected item.
        selected_item = d_(Property(cached=True), writable=False)

        #: Whether the text in the combo box can be edited by the user.
        editable = d_(Bool(False))

        #: A combo box hugs its width weakly by default.
        hug_width = set_default('weak')

        #: A reference to the ProxyComboBox object.
        proxy = Typed(ProxyComboBox)

        @selected_item.getter
        def get_selected_item(self):
            """ The getter function for the selected item property.

            If the index falls out of range, the selected item will be an
            empty string.

            """
            items = self.items
            idx = self.index
            if idx < 0 or idx >= len(items):
                return ''
            return items[idx]

        #--------------------------------------------------------------------------
        # Observers
        #--------------------------------------------------------------------------
        @observe('index', 'items', 'editable')
        def _update_proxy(self, change):
            """ An observer which sends state change to the proxy.

            """
            # The superclass handler implementation is sufficient.
            super(ComboBox, self)._update_proxy(change)

        @observe('index', 'items')
        def _reset_selected_item(self, change):
            """ Reset the selected item when the index or items changes.

            """
            if change['type'] == 'update':
                self.get_member('selected_item').reset(self)