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支持撤消和重做

Supporting Undo and Redo

iPhone OS gives users the ability to undo and redo their typing in text views. 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.

iPhone操作系统在文本视图支持用户撤消和重做他们的输入。用户摇晃设备以启动一个撤销，然后设备显示一个警告，使用户能够撤销他们刚刚打的字，重新输入未完成的编辑，或者继续输入。

UIKit allows you to support undo in a more general way in your application (for information on how to implement this behavior in code, see Undo Architecture). You can specify:

UIKit允许你在你的应用程序里以更普遍的方式支持撤消（关于如何在代码中实施这一行为，请参见"撤消架构"）。你可以指定：

• The actions users can undo or redo
  那些行动是可以被用户撤消或重做的
• When your application should interpret a shake event as the shake to undo gesture
  什么时候你的应用程序应解释一个作为撤消手势的摇晃事件
• How many levels of undo to support
  多少层的撤消被允许

To provide a great user experience for the undo and redo capability in your application, you should:

为了在你的应用里提供一个具有良好用户体验的撤消和重做功能，你应该：

• Supply brief descriptive phrases that tell users precisely what they’re undoing or redoing. UIKit automatically supplies the strings “Undo “ and “Redo “ for the undo alert button titles, but you need to provide a word or two that describes the action users can undo or redo. (Note that the Cancel button cannot be changed.) For example, you might supply the text “Delete Name” or “Address Change,” to create buttons titles such as “Undo Delete Name” or “Redo Address Change.”

用简短的描述性词组，准确地告诉用户他们撤消或重做的是什么。UIKit自动用“撤消”和“重做”作为撤消警告按钮的标题，但你需要提供一两句话来对用户撤消或重做的行为作描述。 （请注意，取消按钮不能更改。）例如，你可能提供诸如“删除名称”或“地址变更” 的按钮,而用“撤消删除名称”或“重做地址更改”作为按钮标题。

Be sure to avoid supplying text that is too long: A button title that is too long is truncated and is difficult for users to decipher. Also, because this text is in a button title, use title-style capitalization and do not add punctuation. (Briefly, title-style capitalization means to capitalize every word except articles, coordinating conjunctions, and prepositions of four or fewer letters.)

一定要避免提供太长的文本：按钮标题过长被截断，使得用户难以识别。此外，由于这个文本是一个按钮标题，应符合标题的字母大写规则和不加标点符号。（简单的说，标题的大写规则意味着大写除了正文的每一个单词，连词和四个或更少的字母的介词。）

• Avoid overloading the shake gesture. Even though you can programmatically set when your application interprets a shake event as shake to undo, you run the risk of confusing users if they also use shake to perform a different action.

避免超载的动摇的姿态。即使你可以以编程方式设置你的应用程序时，一摇解释事件，因为摇撤消，你冒的风险迷惑用户，如果他们还使用摇来执行不同的操作。

The shake gesture is the primary way users expect to initiate undo and redo, but you can also include the system-provided Undo and Redo buttons in a navigation bar, if appropriate. 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.

摇晃是用户期望激发撤消和重做的主要方式，但如果合适,你还可以在导航栏中采用系统提供的撤消和重做按钮。你可以这样做，重要的是你需要显示一个明确的,专门的按钮来执行在应用程序里的这些功能，但是这不是常用的方法。

• Consider the context of the actions you allow to be undone or redone. In general, users expect their changes and actions to take effect immediately. As much as possible, the undo and redo capability should be clearly related to the user’s immediate context, and not to an earlier context.

考虑你所允许的撤消或重做行为涉及的内容。一般情况下，用户期望他们的变化和行为立即生效。尽可能保证撤消和恢复的能力应明确与用户当前情景相连接，而不是一个更早的情景。