The UndoRedoManager provides a complete history of all the user's actions, undos and redos (provided those the users actions notify the UndoRedoManager). Unlike the standard UndoManager, the {@link au.com.forward.undoRedo.UndoRedoManager UndoRedoManager} does not truncate the undo history, nor does it throw away the redo history once the user performs another action.
Undo and Redo work in just the same way as the previous Java UndoManager. The Undo actions are available to be undone by calling {@link au.com.forward.undoRedo.UndoRedoManager#undo undo()} which undoes one action at a time until you reach the initial point of the application. Calling {@link au.com.forward.undoRedo.UndoRedoManager#redo redo()} redoes the last series of undos in the same way the previous Java UndoManager did.
As well as these traditional functions, the UndoReoManager maintains a tree structure which can be displayed to allow the user to select any previous state and undo/redo to that point by selecting that node in the tree and calling {@link au.com.forward.undoRedo.UndoRedoManager#processUndoRedoCommand processUndoRedoCommand()} By default the pressing the Enter key on the selected node performs this action. Use {@link au.com.forward.undoRedo.UndoRedoManager#getTree()} to get the JTree component to add to your layout.
The UndoRedoManager tree keeps a main trunk of all the actions the user has done or redone and which have not been undone, in the order they were performed, most recent at the top.
As actions are undone they are transferred to a Redo branch from which they can be redone. As actions are redone they add a new undo leaf to the top of the tree. As they are undone a Redo branch is created. Each time a user performs a series of Undo actions, a new Redo branch is created, even if the user has previously retraced this same route. This faithfully records the time order of all the user's actions. As well as the usual undo/redo usage, this tree structure could also be directly applied to recording as user's web browsing history.
To assist in navigation, the UndoRedoManager's tree display shows, for each Redo branch, the deepest level redo on that branch. If the branch is displayed with >> it means some its sub-nodes have been redone. That is the user has retraced some way down that that branch.
A strikethrough node means that die() had been called on the node's UndoableEdit.
UndoRedoManager never calls die() but will not undo or redo past a dead node.
A dead node effectively isolates the main trunk below that point. If the user tries to undo/redo past a dead node then
the unreachable nodes are shown as grey strikethrough. These nodes are not dead,
but they cannot be redone/undone because of a dead node higher up.
Insignificant nodes (isSignificant()==false) are displayed in grey but otherwise not handled differently from other nodes. If you want to omit processing insignificant nodes, either extend UnodRedoManager to ignore then in UndoRedoManager.undoableEditHappened() or write you undoableEdit class to do nothing on undo/redo for insignificant edits.
TODO: The UndoRedo class does not implement addEdit() and replaceEdit(), so compound edits need to be collected before calling UndoRedoManager.undoableEditHappened().
The optional features are enabled by implement interfaces in your undoableEdit class. The ICanBeRolledBack interface causes the UndoRedoManager to create a framemarker which can be used to roll back the undo/redo tree. The IHaveDescription interface provides access to an extended description of the action. It uses a callback so you can defer creating the description until it is requested. To display the descriptions just add the UndoRedoManager to your layout. The UndoRedoManager extends JSplitPane and displays the tree on the left and the description on the right. You can also get the display text component separately or supply your own.
UndoRedo Package
Copyright (c)2005 Forward Computing and Control Pty. Ltd.
NSW. Australia, www.forward.com.au
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