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### Copyright (C) 2002-2006 Stephen Kennedy <stevek@gnome.org>
### This program is free software; you can redistribute it and/or modify
### it under the terms of the GNU General Public License as published by
### the Free Software Foundation; either version 2 of the License, or
### (at your option) any later version.
### This program is distributed in the hope that it will be useful,
### but WITHOUT ANY WARRANTY; without even the implied warranty of
### MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
### GNU General Public License for more details.
### You should have received a copy of the GNU General Public License
### along with this program; if not, write to the Free Software
### Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""Module to help implement undo functionality.
Usage:
t = TextWidget()
s = UndoSequence()
def on_textwidget_text_inserted():
s.begin_group()
if not t.is_modified():
s.add_action( TextWidgetModifiedAction() )
s.add_action( InsertionAction() )
s.end_group()
def on_undo_button_pressed():
s.undo()
"""
import gobject
class GroupAction(object):
"""A group action combines several actions into one logical action.
"""
def __init__(self, seq):
self.seq = seq
def undo(self):
while self.seq.can_undo():
self.seq.undo()
def redo(self):
while self.seq.can_redo():
self.seq.redo()
class UndoSequence(gobject.GObject):
"""A manager class for operations which can be undone/redone.
"""
__gsignals__ = {
'can-undo': (gobject.SIGNAL_RUN_FIRST, gobject.TYPE_NONE, (gobject.TYPE_BOOLEAN,)),
'can-redo': (gobject.SIGNAL_RUN_FIRST, gobject.TYPE_NONE, (gobject.TYPE_BOOLEAN,))
}
def __init__(self):
"""Create an empty UndoSequence.
"""
self.__gobject_init__()
self.actions = []
self.next_redo = 0
self.group = None
def clear(self):
"""Remove all undo and redo actions from this sequence
If the sequence was previously able to undo and/or redo, the
'can-undo' and 'can-redo' signals are emitted.
Raises an AssertionError if a group is in progress.
"""
if hasattr(self, "group"):
assert self.group == None
if self.can_undo():
self.emit('can-undo', 0)
if self.can_redo():
self.emit('can-redo', 0)
self.actions = []
self.next_redo = 0
self.group = None
def can_undo(self):
"""Return if an undo is possible.
"""
return self.next_redo > 0
def can_redo(self):
"""Return if a redo is possible.
"""
return self.next_redo < len(self.actions)
def add_action(self, action):
"""Add an action to the undo list.
Arguments:
action -- A class with two callable attributes: 'undo' and 'redo'
which are called by this sequence during an undo or redo.
"""
if self.group == None:
could_undo = self.can_undo()
could_redo = self.can_redo()
self.actions[self.next_redo:] = []
self.actions.append(action)
self.next_redo += 1
if not could_undo:
self.emit('can-undo', 1)
if could_redo:
self.emit('can-redo', 0)
else:
self.group.add_action(action)
def undo(self):
"""Undo an action.
Raises an AssertionError if the sequence is not undoable.
"""
assert self.next_redo > 0
could_redo = self.can_redo()
self.next_redo -= 1
self.actions[self.next_redo].undo()
if not self.can_undo():
self.emit('can-undo', 0)
if not could_redo:
self.emit('can-redo', 1)
def redo(self):
"""Redo an action.
Raises and AssertionError if the sequence is not undoable.
"""
assert self.next_redo < len(self.actions)
could_undo = self.can_undo()
a = self.actions[self.next_redo]
self.next_redo += 1
a.redo()
if not could_undo:
self.emit('can-undo', 1)
if not self.can_redo():
self.emit('can-redo', 0)
def begin_group(self):
"""Group several actions into a single logical action.
Whey you Wrap several calls to add_action() inside begin_group()
and end_group(), all the intervening actions are considered
one logical action. For instance a 'replace' action may be
implemented as a pair of 'delete' and 'create' actions, but
undoing should undo both of them.
"""
if self.group:
self.group.begin_group()
else:
self.group = UndoSequence()
def end_group(self):
"""End a logical group action. See also begin_group().
Raises an AssertionError if there was not a matching call to
begin_group().
"""
assert self.group != None
if self.group.group != None:
self.group.end_group()
else:
group = self.group
self.group = None
if len(group.actions) == 1: # collapse
self.add_action( group.actions[0] )
elif len(group.actions) > 1:
self.add_action( GroupAction(group) )
def abort_group(self):
"""Revert the sequence to the state before begin_group() was called.
Raises an AssertionError if there was no a matching call to begin_group().
"""
assert self.group != None
if self.group.group != None:
self.group.abort_group()
else:
self.group = None
if gobject.pygtk_version < (2,8,0):
gobject.type_register(UndoSequence)
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