Performing Undo and Redo
Performing undo and redo is usually as simple as sending undo
and redo
messages to an NSUndoManager
object. The undo
message closes the last open undo group and then applies all the undo operations in that group (recording any undo operations as redo operations instead). The redo
message likewise applies all the redo operations on the top redo group.
The undo
method is intended for undoing top-level groups, and should not be used for nested undo groups. If any unclosed, nested undo groups are on the stack when undo
is invoked, it raises an exception. To undo nested groups, you must explicitly close the group with an endUndoGrouping
message, then use undoNestedGroup
to undo it. Note also that if you turn off automatic grouping by event with setGroupsByEvent:
, you must explicitly close the current undo group with endUndoGrouping
before invoking either undo method.
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