Undo Redo Design

From Event-B
Jump to: navigation, search

History Mechanism

Undo / Redo is built on top of the history mechanism provided by Eclipse [1]. It is composed of class History and interface IUndoableOperation. Each operation has three methods to act on the database:
execute()
,
undo()
and
redo()
. Database changes are added to the history. The
execute()
operation is called during addition. Then, operations
undo()
and
redo()
are executed by the history when an Undo or Redo action is performed.

As each file has its own history, every operation has a context, which is the name of the file. The History class just manages the history of all files.

Implementation for Rodin

First, we have to make objects that implement IUndoableOperation for each transaction on the database. We use the composite model so that each operation is composed of basic operations (add an element, delete an element, change an attribute ,...). The operations are created by a factory.

Some operations are dependent on an element in their execution (e.g., change an attribute). This may not be known when recording the operation in the History. To do this, operations have methods
getCreatedElement()
and
setParent()
which are called by
execute()
.

Then to ensure atomicity with respects to the Rodin database, composite operations (TreeOperation) are encapsulated in a class AtomicOperation. It only delegates its methods but it encapsulates in the RodinCore.run().

Available Interface

The interface provided to clients consists of three class:

  • OperationFactory
  • History
  • AtomicOperation

The factory may not be instantiated and its methods are static. History implements the pattern Singleton and delegates to IOperationHistory.