我已经读过使用命令模式是实现执行/撤消功能的最常用方法之一。实际上,我已经看到可以堆叠一堆动作并反转它们以达到给定状态。但是,我不太确定如何在Python中完成这些工作以及我阅读的大部分教程,涉及到概念,但没有在Python中显示实际的实现。
有谁知道在Python中如何/撤消功能?
作为参考,这是我的(天真的,可能是错误的)错误代码:
# 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,此测试不允许堆栈多个操作撤消。也许我完全错了所以我会感激一些帮助。
答案 0 :(得分:2)
我如何解决这个问题
class Command(object):
def execute(self, canvas):
raise NotImplementedError
class DrawLineCommand(Command):
def __init__(self, point1, point2):
self._point1 = point1
self._point2 = point2
def execute(self, canvas):
canvas.draw_line(self._point1, self._point2)
class DrawCircleCommand(Command):
def __init__(self, point, radius):
self._point = point
self._radius = radius
def execute(self, canvas):
canvas.draw_circle(self._point, self._radius)
class UndoHistory(object):
def __init__(self, canvas):
self._commands = []
self.canvas = canvas
def command(self, command):
self._commands.append(command)
command.execute(self.canvas)
def undo(self):
self._commands.pop() # throw away last command
self.canvas.clear()
for command self._commands:
command.execute(self.canvas)
一些想法:
答案 1 :(得分:2)
这是一个将命令保存在列表中的实现。
# 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)