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Class UndoManager

Hierarchy

  • UndoManager

UndoManager observes and records model and diagram changes in transactions and supports undo/redo operations. You will need to set the isEnabled property to true in order for users to perform an undo or a redo.

Typically an operation will call startTransaction, make some changes to the Model or Diagram, and then call commitTransaction. Any ChangedEvents that occur will be recorded in a Transaction object. If for some reason you do not wish to complete the transaction successfully, you can call rollbackTransaction instead of commitTransaction.

The history property is a list of Transactions. commitTransaction will add the currentTransaction to the history list. rollbackTransaction will undo the changes remembered in the currentTransaction and then discard it, without changing the history. You can limit how many transactions are remembered in the history by setting maxHistoryLength.

Transactions may be nested. Be sure to call either commitTransaction or rollbackTransaction for each call to startTransaction. Avoid repeated start-commit-start-commit calls as a result of a user's actions. Instead, start, make all changes, and then commit.

If you want to restore the diagram to the state before the latest complete transaction, call undo. Call redo to change the diagram to a later state. If after some number of undo's you start a transaction, all of the history after the current state is discarded, and a new transaction may be recorded. You cannot undo or redo during a transaction.

Initially each Model has its own UndoManager. UndoManagers may be shared by multiple Models by replacing the standard Model.undoManager created by the model constructor.

There are several informational properties:

Index

Constructors

constructor

  • The constructor produces an empty UndoManager with no transaction history.

    Returns UndoManager

Properties

Read-only currentTransaction : Transaction | null

  • This read-only property returns the current Transaction for recording additional model change events. This is initialized and augmented by handleChanged before it is added to history by a top-level call to commitTransaction. The value will be null between transactions.

Read-only history : List<Transaction>

  • This read-only property returns the whole history, a list of all of the Transactions, each representing a transaction with some number of ChangedEvents.

    You should not modify this List.

Read-only historyIndex : number

  • This read-only property returns the index into history for the current undoable Transaction. The value is -1 if there is no undoable Transaction to be undone.

isEnabled : boolean

  • Gets or sets whether this UndoManager records any changes. The default value is false -- you need to set this to true if you want the user to be able to undo or redo.

    You can temporarily turn off recording by setting Diagram.skipsUndoManager and Model.skipsUndoManager to true.

Read-only isInTransaction : boolean

Read-only isUndoingRedoing : boolean

  • This read-only property is true during a call to undo or redo.

maxHistoryLength : number

  • Gets or sets the maximum number of transactions that this undo manager will remember. When a transaction is committed and the number exceeds this value, the UndoManager will discard the oldest transaction(s). The initial value is 999. A negative value is treated as if there were no limit.

    This property is useful in helping limit the memory consumption of typical applications. But this does not limit the number of ChangedEvents that are recorded, because there may be an unlimited number of those within each Transaction. Decreasing this value will not necessarily remove any existing Transactions if there currently exist more in history than the new value permits.

Read-only models : Iterator<Model>

  • This read-only property returns an iterator for all of the Models that this UndoManager is handling.

    see

    addModel, removeModel

Read-only nestedTransactionNames : List<string>

  • This read-only property returns a stack of ongoing transaction names. The outermost transaction name will be the first item in the list. The last one will be the name of the most recent (nested) call to startTransaction.

    You should not modify this List.

Read-only transactionLevel : number

  • This read-only property returns the current transaction level. The value is zero when there is no ongoing transaction. The initial value is zero. startTransaction will increment this value; commitTransaction or rollbackTransaction will decrement it. When this value is greater than zero, canUndo and canRedo will be false, because additional logically related model change events may occur.

Read-only transactionToRedo : Transaction | null

  • This read-only property returns the Transaction in the history to be redone next. The value may be null if the UndoManager is not ready to perform a redo.

    see

    transactionToUndo

Read-only transactionToUndo : Transaction | null

  • This read-only property returns the Transaction in the history to be undone next. The value may be null if the UndoManager is not ready to perform an undo.

    see

    transactionToRedo

Methods

addModel

  • addModel(model: Model): void
  • Make sure this UndoManager knows about a Model for which it may receive ChangedEvents when the given Model is changed. The model will also receive notifications about transactions and undo or redo operations.

    You should not call this method during a transaction.

    see

    models, removeModel

    Parameters

    • model: Model

      A Model that this UndoManager is managing.

    Returns void

canRedo

  • canRedo(): boolean
  • This predicate returns true if you can call redo. This will return false if isEnabled is false (as it is by default), if any transaction is ongoing, or if there is no transactionToRedo that can be redone.

    Returns boolean

    true if ready for redo to be called.

canUndo

  • canUndo(): boolean
  • This predicate returns true if you can call undo. This will return false if isEnabled is false (as it is by default), if any transaction is ongoing, or if there is no transactionToUndo that can be undone.

    Returns boolean

    true if ready for undo to be called.

clear

  • clear(): void
  • Clear all of the Transactions and clear all other state, including any ongoing transaction without rolling back. However, this maintains its references to its Models.

    You should not call this method during a transaction.

    Returns void

commitTransaction

  • commitTransaction(tname?: string): boolean

handleChanged

redo

  • redo(): void

removeModel

  • removeModel(model: Model): void
  • Inform this UndoManager that it will no longer be receiving ChangedEvents when the given Model is changed. The model will no longer receive notifications about transactions and undo or redo operations.

    You should not call this method during a transaction. If you call this method between transactions when there is a transaction history, you should be careful that there are no ChangedEvents referring to that model in any Transactions.

    see

    models, addModel

    Parameters

    • model: Model

      A Model that this UndoManager should no longer manage.

    Returns void

rollbackTransaction

  • rollbackTransaction(): boolean

Virtual skipsEvent

startTransaction

  • startTransaction(tname?: string): boolean

undo

  • undo(): void