JUCE/modules/juce_gui_basics/keyboard/juce_KeyboardFocusTraverser.h

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2015 - ROLI Ltd.

   Permission is granted to use this software under the terms of either:
   a) the GPL v2 (or any later version)
   b) the Affero GPL v3

   Details of these licenses can be found at: www.gnu.org/licenses

   JUCE is distributed in the hope that it will be useful, but WITHOUT ANY
   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
   A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

   ------------------------------------------------------------------------------

   To release a closed-source product which uses JUCE, commercial licenses are
   available: visit www.juce.com for more information.

  ==============================================================================
*/

#pragma once


//==============================================================================
/**
    Controls the order in which focus moves between components.

    The default algorithm used by this class to work out the order of traversal
    is as follows:
    - if two components both have an explicit focus order specified, then the
      one with the lowest number comes first (see the Component::setExplicitFocusOrder()
      method).
    - any component with an explicit focus order greater than 0 comes before ones
      that don't have an order specified.
    - any unspecified components are traversed in a left-to-right, then top-to-bottom
      order.

    If you need traversal in a more customised way, you can create a subclass
    of KeyboardFocusTraverser that uses your own algorithm, and use
    Component::createFocusTraverser() to create it.

    @see Component::setExplicitFocusOrder, Component::createFocusTraverser
*/
class JUCE_API  KeyboardFocusTraverser
{
public:
    KeyboardFocusTraverser();

    /** Destructor. */
    virtual ~KeyboardFocusTraverser();

    /** Returns the component that should be given focus after the specified one
        when moving "forwards".

        The default implementation will return the next component which is to the
        right of or below this one.

        This may return nullptr if there's no suitable candidate.
    */
    virtual Component* getNextComponent (Component* current);

    /** Returns the component that should be given focus after the specified one
        when moving "backwards".

        The default implementation will return the next component which is to the
        left of or above this one.

        This may return nullptr if there's no suitable candidate.
    */
    virtual Component* getPreviousComponent (Component* current);

    /** Returns the component that should receive focus be default within the given
        parent component.

        The default implementation will just return the foremost child component that
        wants focus.

        This may return nullptr if there's no suitable candidate.
    */
    virtual Component* getDefaultComponent (Component* parentComponent);
};