juce/source/src/utilities/juce_UndoableAction.h

   1 /*
   2   ==============================================================================
   3
   4    This file is part of the JUCE library - "Jules' Utility Class Extensions"
   5    Copyright 2004-11 by Raw Material Software Ltd.
   6
   7   ------------------------------------------------------------------------------
   8
   9    JUCE can be redistributed and/or modified under the terms of the GNU General
  10    Public License (Version 2), as published by the Free Software Foundation.
  11    A copy of the license is included in the JUCE distribution, or can be found
  12    online at www.gnu.org/licenses.
  13
  14    JUCE is distributed in the hope that it will be useful, but WITHOUT ANY
  15    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  16    A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
  17
  18   ------------------------------------------------------------------------------
  19
  20    To release a closed-source product which uses JUCE, commercial licenses are
  21    available: visit www.rawmaterialsoftware.com/juce for more information.
  22
  23   ==============================================================================
  24 */
  25
  26 #ifndef __JUCE_UNDOABLEACTION_JUCEHEADER__
  27 #define __JUCE_UNDOABLEACTION_JUCEHEADER__
  28
  29
  30 //==============================================================================
  31 /**
  32     Used by the UndoManager class to store an action which can be done
  33     and undone.
  34
  35     @see UndoManager
  36 */
  37 class JUCE_API  UndoableAction
  38 {
  39 protected:
  40     /** Creates an action. */
  41     UndoableAction() noexcept   {}
  42
  43 public:
  44     /** Destructor. */
  45     virtual ~UndoableAction()   {}
  46
  47     //==============================================================================
  48     /** Overridden by a subclass to perform the action.
  49
  50         This method is called by the UndoManager, and shouldn't be used directly by
  51         applications.
  52
  53         Be careful not to make any calls in a perform() method that could call
  54         recursively back into the UndoManager::perform() method
  55
  56         @returns    true if the action could be performed.
  57         @see UndoManager::perform
  58     */
  59     virtual bool perform() = 0;
  60
  61     /** Overridden by a subclass to undo the action.
  62
  63         This method is called by the UndoManager, and shouldn't be used directly by
  64         applications.
  65
  66         Be careful not to make any calls in an undo() method that could call
  67         recursively back into the UndoManager::perform() method
  68
  69         @returns    true if the action could be undone without any errors.
  70         @see UndoManager::perform
  71     */
  72     virtual bool undo() = 0;
  73
  74     //==============================================================================
  75     /** Returns a value to indicate how much memory this object takes up.
  76
  77         Because the UndoManager keeps a list of UndoableActions, this is used
  78         to work out how much space each one will take up, so that the UndoManager
  79         can work out how many to keep.
  80
  81         The default value returned here is 10 - units are arbitrary and
  82         don't have to be accurate.
  83
  84         @see UndoManager::getNumberOfUnitsTakenUpByStoredCommands,
  85              UndoManager::setMaxNumberOfStoredUnits
  86     */
  87     virtual int getSizeInUnits()    { return 10; }
  88
  89     /** Allows multiple actions to be coalesced into a single action object, to reduce storage space.
  90
  91         If possible, this method should create and return a single action that does the same job as
  92         this one followed by the supplied action.
  93
  94         If it's not possible to merge the two actions, the method should return zero.
  95     */
  96     virtual UndoableAction* createCoalescedAction (UndoableAction* nextAction)  { (void) nextAction; return nullptr; }
  97 };
  98
  99
 100 #endif   // __JUCE_UNDOABLEACTION_JUCEHEADER__