Package com.levigo.jadice.web.client.undo

Interface UndoManager

All Known Implementing Classes:
DefaultUndoManager, NoopUndoManager
public interface UndoManager
An UndoManager is responsible for the management of actions a user takes in some kind of UI and providing means of undoing and redoing those actions.

Actions are represented by UndoableEdits. Undoable edits encapsulate those actions at a granularity that is up to the implementor. In general, it is desirable to neither make them too fine-grained (don't undo every single key-press for some typed text) nor too coarse, so that an undo loses a large amount of work. UndoableEdit.tryMergeInto(UndoableEdit) can be used to manage the granularity.

The undo manager will usually maintain two stacks of actions: the undo stack and the redo stack. The sizes of those stacks may be limited, so that the undo history doesn't become too large. The general undo algorithm is as follows:

  • Edits are added to the undo stack using addEdit(UndoableEdit).
  • Calling undo() will instruct the action at the top of the stack to undo its effect, then add the edit to the redo stack.
  • Calling undo() will instruct the action at the top of the stack to redo its effect, then add the edit back to the undo stack.
  • Adding an edit while the redo strack is non-empty will clear the redo stack making that path of action no longer accessible.

  • Method Details

    • clear

      void clear()
      Clear the undo and redo stacks.

    • undo

      void undo() throws CannotUndoException
      Undo the edit at the top of the undo stack.
      Throws:
      CannotUndoException - if the stack is empty or the edit cannot be undone for some other reason.

    • canUndo

      boolean canUndo()
      Determine whether there is currently something to undo.
      Returns:
      true if there is

    • redo

      void redo() throws CannotRedoException
      Redo the edit at the top of the redo stack.
      Throws:
      CannotRedoException - if the stack is empty or the edit cannot be re-done for some other reason.

    • canRedo

      boolean canRedo()
      Determine whether there is currently something to redo.
      Returns:
      true if there is

    • addEdit

      boolean addEdit(UndoableEdit anEdit)
      Add an undoable edit to the undo stack. This can happen in one of two ways:
      • The edit could not be merged into the element currently at the top of the stack either because the stack was empty or because the UndoableEdit.tryMergeInto(UndoableEdit) returned false. In this case the new edit is simply added to the stack.
      • The edit could me berged.
      Parameters:
      anEdit - the edit
      Returns:
      true if the edit was merged into the edit at the top of the stack, false otherwise.

    • getUndoDescription

      String getUndoDescription()
      Get the human-readable description of the edit at the top of the undo stack. It is provided by delegating to UndoableEdit.getUndoDescription().
      Returns:
      the description or null if the undo stack is empty.

    • getRedoDescription

      String getRedoDescription()
      Get the human-readable description of the edit at the top of the redo stack. It is provided by delegating to UndoableEdit.getRedoDescription().
      Returns:
      the description or null if the redo stack is empty.

    • addOnUndoStackUpdatedHandler

      void addOnUndoStackUpdatedHandler(OnUndoStackUpdatedHandler handler)
      Adds a handler that is called whenever the undo/redo item lists are updated.
      Parameters:
      handler - The handler to add.

    • removeOnUndoStackUpdatedHandler

      void removeOnUndoStackUpdatedHandler(OnUndoStackUpdatedHandler handler)
      Removes a handler that is called whenever the undo/redo item lists are updated.
      Parameters:
      handler - The handler to remove.

    • clearOnUndoStackUpdateHandlers

      void clearOnUndoStackUpdateHandlers()
      Removes all handlers that are called whenever the undo/redo item lists are updated.