在编辑、撤销和重做的过程中，模型是唯一保持不变的。
During the course of editing, undo, and redo, the model is the only thing that endures.
这个魔法的中心是撤销和重做的能力。
命令可用来验证用户的交互，并且提供撤销和重做支持。
Commands can be used to validate the user's interaction, and to provide undo and redo support.
WireframeSketcher具有所有的习惯操作方法例如复制、粘贴以及无穷的撤销重做。
WireframeSketcher has all the usual editor functionality such as copy&paste and an infinite undo-redo.
如有必要，你可以在屏幕上显示一个明确的，专用的按钮用于在你的应用程序中执行这些功能(撤销与重做)，但是这不是常用的方法。
You might do this if it's essential that you display an explicit, dedicated button to perform these functions within the context of your application, but this is unusual.
用户摇晃设备启动撤销，接着设备将显示警告，允许用户撤销他们刚刚输入的内容，重做之前撤销的内容，或取消撤销。
Users initiate an undo by shaking the device, which displays an alert that allows users to undo what they just typed, redo previously undone typing, or cancel the undo.
你可以使用重做命令来扭转撤销命令进行的操作。
You can reverse the action of the Undo command by using the Redo command.
命令模式的使用包含整个类框架设计和几套图形编辑操作子类设计，支持可以撤销重做的操作。
The command design pattern which provides undo-redo operation, is applied to the whole class frame design and several sub-classes design of graphics edit operation.
命令模式的使用包含整个类框架设计和几套图形编辑操作子类设计，支持可以撤销重做的操作。
The command design pattern which provides undo-redo operation, is applied to the whole class frame design and several sub-classes design of graphics edit operation.
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