View source for Undo and redo

Wandora application stores all topic map operations and user can undo these operations one by one. Reader should note that Wandora can't undo all operations but only '''topic map''' operations such as topic creation and variant name change. Also, deletion or creation of a complete topic map layer can not be undone.

Undo is performed by selecting a menu option '''Edit > Undo'''.

Successful undo generates no log messages. If undo is not possible, Wandora views a log message.

Undo buffer groups all topic map operations of an executed tool, and undo cancels every change in the group. For example, user generates topics and associations using [[L-system generator]]. Once generator finishes, user triggers undo and all topics and associations generated by the L-system generator are deleted (unless they already were in the topic map before the L-system generation).

Once a topic map operation group is undone, it can be redone by selecting a menu option '''Edit > Redo'''. Reader should note that redo option disappers after another topic map operation. It is not possible to redo a topic map operation after the topic map has changed.

To view undo buffer, Wandora user can hold CTRL key down while selecting either menu option '''Edit > Undo''' or menu option '''Edit > Redo'''. Wandora view the undo buffer in a sortable table with colums for '''index''', '''undo label''' and '''is marker''', for example. Undo buffer dialog window has buttons to perform an undo and redo, and to clear the undo buffer. If undo buffer is cleared, undo is not possible until the user makes additional topic map changes.

Size of the undo buffer increases after every operation. To prevent undo buffer filling up the memory completely Wandora keeps track of the size of the undo buffer and deletes oldest operations after a given size is exceeded. At the moment, undo buffer can hold up to 50000 topic map operations until oldest are removed. Wandora informs while the limit is exceeded for the first time. Reader should note that large/wide topic map operations may generate more that 50000 operations. For example, merging a topic map with 50000 topics and associations surely causes undo buffer to flush.