这个魔法的中心是撤销和重做的能力。

At the heart of this magic is the ability to undo and redo.

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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.

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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.

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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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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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