在Python中使用命令模式执行/撤消 [英] Do/Undo using command pattern in Python
问题描述
我读过,使用命令模式是完成do / undo功能的最流行的方法之一。事实上,我已经看到,有可能堆叠一堆动作,扭转它们以达到给定的状态。但是,我不太确定如何在Python和我阅读的大部分教程,可以做到概念,但不显示在Python中的实际实现。
I have read that using command pattern is one of the most popular ways to accomplish do/undo functionality. In fact, I have seen that it's possible to stack a bunch of actions and reverse them in order to reach a given state. However, I'm not quite sure how that can be done in Python and most of the tutorials I have read, dabble into concepts but don't show an actual implementation in Python.
有没有人知道Python中的do / undo功能如何工作?
Does anyone know how do/undo functionality work in Python?
为了参考,这是我的(天真的,可能有错误)代码:
For reference, this is my (naive and probably ridden with errors) code:
# command
class DrawCommand:
def __init__(self, draw, point1, point2):
self.draw = draw
self.point1 = point1
self.point2 = point2
def execute_drawing(self):
self.draw.execute(self.point1, self.point2)
def execute_undrawing(self):
self.draw.unexecute(self.point1, self.point2)
# invoker
class InvokeDrawALine:
def command(self, command):
self.command = command
def click_to_draw(self):
self.command.execute_drawing()
def undo(self):
self.command.execute_undrawing()
# receiver
class DrawALine:
def execute(self, point1, point2):
print("Draw a line from {} to {}".format(point1, point2))
def unexecute(self, point1, point2):
print("Erase a line from {} to {}".format(point1, point2))
实例化如下:
invoke_draw = InvokeDrawALine()
draw_a_line = DrawALine()
draw_command = DrawCommand(draw_a_line, 1, 2)
invoke_draw.command(draw_command)
invoke_draw.click_to_draw()
invoke_draw.undo()
输出:
Draw a line from 1 to 2
Erase a line from 1 to 2
显然,不允许堆栈几个动作撤消。
Obviously, this test doesn't allow stack several actions to undo. Maybe I'm completely mistaken so I would appreciate some help.
推荐答案
下面是一个将命令保存在列表中的实现。 / p>
Here is an implementation keeping the commands in a list.
# command
class DrawCommand:
def __init__(self, draw, point1, point2):
self.draw = draw
self.point1 = point1
self.point2 = point2
def execute_drawing(self):
self.draw.execute(self.point1, self.point2)
# invoker
class InvokeDrawLines:
def __init__(self, data):
self.commandlist = data
def addcommand(self, command):
self.commandlist.append(command)
def draw(self):
for cmd in self.commandlist:
cmd.execute_drawing()
def undocommand(self, command):
self.commandlist.remove(command)
# receiver
class DrawALine:
def execute(self, point1, point2):
print("Draw a line from" , point1, point2)
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