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juce_UndoableAction.h
1 
2 /** @weakgroup juce_data_structures-undomanager
3  * @{
4  */
5 /*
6  ==============================================================================
7 
8  This file is part of the JUCE library.
9  Copyright (c) 2017 - ROLI Ltd.
10 
11  JUCE is an open source library subject to commercial or open-source
12  licensing.
13 
14  By using JUCE, you agree to the terms of both the JUCE 5 End-User License
15  Agreement and JUCE 5 Privacy Policy (both updated and effective as of the
16  27th April 2017).
17 
18  End User License Agreement: www.juce.com/juce-5-licence
19  Privacy Policy: www.juce.com/juce-5-privacy-policy
20 
21  Or: You may also use this code under the terms of the GPL v3 (see
22  www.gnu.org/licenses).
23 
24  JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
25  EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
26  DISCLAIMED.
27 
28  ==============================================================================
29 */
30 
31 namespace juce
32 {
33 
34 //==============================================================================
35 /**
36  Used by the UndoManager class to store an action which can be done
37  and undone.
38 
39  @see UndoManager
40 
41  @tags{DataStructures}
42 */
44 {
45 protected:
46  /** Creates an action. */
47  UndoableAction() = default;
48 
49 public:
50  /** Destructor. */
51  virtual ~UndoableAction() = default;
52 
53  //==============================================================================
54  /** Overridden by a subclass to perform the action.
55 
56  This method is called by the UndoManager, and shouldn't be used directly by
57  applications.
58 
59  Be careful not to make any calls in a perform() method that could call
60  recursively back into the UndoManager::perform() method
61 
62  @returns true if the action could be performed.
63  @see UndoManager::perform
64  */
65  virtual bool perform() = 0;
66 
67  /** Overridden by a subclass to undo the action.
68 
69  This method is called by the UndoManager, and shouldn't be used directly by
70  applications.
71 
72  Be careful not to make any calls in an undo() method that could call
73  recursively back into the UndoManager::perform() method
74 
75  @returns true if the action could be undone without any errors.
76  @see UndoManager::perform
77  */
78  virtual bool undo() = 0;
79 
80  //==============================================================================
81  /** Returns a value to indicate how much memory this object takes up.
82 
83  Because the UndoManager keeps a list of UndoableActions, this is used
84  to work out how much space each one will take up, so that the UndoManager
85  can work out how many to keep.
86 
87  The default value returned here is 10 - units are arbitrary and
88  don't have to be accurate.
89 
90  @see UndoManager::getNumberOfUnitsTakenUpByStoredCommands,
91  UndoManager::setMaxNumberOfStoredUnits
92  */
93  virtual int getSizeInUnits() { return 10; }
94 
95  /** Allows multiple actions to be coalesced into a single action object, to reduce storage space.
96 
97  If possible, this method should create and return a single action that does the same job as
98  this one followed by the supplied action.
99 
100  If it's not possible to merge the two actions, the method should return a nullptr.
101  */
102  virtual UndoableAction* createCoalescedAction (UndoableAction* nextAction) { ignoreUnused (nextAction); return nullptr; }
103 };
104 
105 } // namespace juce
106 
107 /** @}*/
#define JUCE_API
This macro is added to all JUCE public class declarations.
virtual int getSizeInUnits()
Returns a value to indicate how much memory this object takes up.
virtual UndoableAction * createCoalescedAction(UndoableAction *nextAction)
Allows multiple actions to be coalesced into a single action object, to reduce storage space...
Used by the UndoManager class to store an action which can be done and undone.