.. wxPython Phoenix documentation

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   Copyright: (c) 2011-2020 by Total Control Software
   License:   wxWindows License

.. include:: headings.inc

.. currentmodule:: wx.lib.docview

.. highlight:: python



.. _wx.lib.docview.Command:

==========================================================================================================================================
|phoenix_title|  **wx.lib.docview.Command**
==========================================================================================================================================

``Command`` is a base class for modelling an application command,
which is an action usually performed by selecting a menu item, pressing a
toolbar button or any other means provided by the application to
change the data or view.



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|class_hierarchy| Class Hierarchy
=================================

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   Inheritance diagram for class <strong>Command</strong>:
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   <div id="toggleBlock-content" style="display:none;">
   <p class="graphviz">
   <center><img src="_static/images/inheritance/wx.lib.docview.Command_inheritance.png" alt="Inheritance diagram of Command" usemap="#dummy" class="inheritance"/></center>
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|super_classes| Known Superclasses
==================================

:class:`wx.Object`

|


|method_summary| Methods Summary
================================

================================================================================ ================================================================================
:meth:`~wx.lib.docview.Command.__init__`                                         Constructor. :class:`Command` is an abstract class, so you will need to
:meth:`~wx.lib.docview.Command.CanUndo`                                          Returns ``True`` if the command can be undone, false otherwise.
:meth:`~wx.lib.docview.Command.Do`                                               Override this member function to execute the appropriate action when
:meth:`~wx.lib.docview.Command.GetName`                                          Returns the command name.
:meth:`~wx.lib.docview.Command.Undo`                                             Override this member function to un-execute a previous :meth:`Do`.
================================================================================ ================================================================================


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|api| Class API
===============


.. class:: Command(wx.Object)

   ``Command`` is a base class for modelling an application command,
   which is an action usually performed by selecting a menu item, pressing a
   toolbar button or any other means provided by the application to
   change the data or view.

   .. method:: __init__(self, canUndo = False, name = None)

      Constructor. :class:`Command` is an abstract class, so you will need to
      derive a new class and call this constructor from your own constructor.
      
      ``canUndo`` tells the command processor whether this command is undo-able.
      You can achieve the same functionality by overriding the CanUndo member
      function (if for example the criteria for undoability is context-
      dependent).
      
      ``name`` must be supplied for the command processor to display the command
      name in the application's edit menu.


   .. method:: CanUndo(self)

      Returns ``True`` if the command can be undone, false otherwise.


   .. method:: Do(self)

      Override this member function to execute the appropriate action when
      called. Return ``True`` to indicate that the action has taken place, false
      otherwise. Returning false will indicate to the command processor that
      the action is not undoable and should not be added to the command
      history.


   .. method:: GetName(self)

      Returns the command name.


   .. method:: Undo(self)

      Override this member function to un-execute a previous :meth:`Do`.
      Return ``True`` to indicate that the action has taken place, ``False``
      otherwise. Returning ``False`` will indicate to the command processor
      that the action is not redoable and no change should be made to the
      command history.
      
      How you implement this command is totally application dependent, but
      typical strategies include:
      
      Perform an inverse operation on the last modified piece of data in the
      document. When redone, a copy of data stored in command is pasted back
      or some operation reapplied. This relies on the fact that you know the
      ordering of Undos; the user can never Undo at an arbitrary position in
      he command history.
      
      Restore the entire document state (perhaps using document
      transactioning). Potentially very inefficient, but possibly easier to
      code if the user interface and data are complex, and an 'inverse
      execute' operation is hard to write.