出自UXGuide.net

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操作系统支持用户在文本视图输入时，使用撤销和重做。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。

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正规的方式支持撤消（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
  哪些操作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该把摇晃事件解释为撤销手势
• How many levels of undo to support
  最多支持多少次撤销

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

为了保证你的应用程序中的撤消和重做功能具有良好的用户体验，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，准确地告知用户他们正在撤消或重做的是什么。UIKit自动使用“撤消 ”和“重做 ”作为撤消警告按钮的标题，但你需再增加一两个单词描述用户撤消或重做的操作。（请注意，取消按钮文字不能更改。）例如，你可能增加诸如“删除名称”或“地址变更” 这样的单词，这样“撤消删除名称”或“重做地址更改”将作为按钮标题。

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：按钮标题过长导致被截断，用户就难以解读。此外，由于这个文本是一个按钮标题，应使用标题风格的大写规则，并且不加标点。（简单的说，标题风格的大写规则意思是，除去冠词，并列联句，和四个或少于四个字母的介词之外，其他单词首字母都大写。）

• 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.

避免过度使用摇晃手势。尽管你可以程序化地设置你的应用程序什么时候把摇晃事件解释为撤销手势，你还是面临着让用户迷惑的风险，因为用户可能使用摇晃手势去执行另外的操作。

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.

摇晃是用户期望启动撤消和重做的首要方法，但如果可以的话，你也可以在导航栏中包含系统提供的撤消和重做按钮。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。

• 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操作的环境。一般来说下，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环境相关，而不是与更早前环境相关。