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用于导航栏、工具栏和标签栏的图标

Icons for Navigation Bars, Toolbars, and Tab Bars

When possible, you should use the system-provided buttons and icons in navigation bars, toolbars, and tab bars. iPhone OS provides a wide range of standard buttons and icons that users associate with standard tasks and modes supported in the built-in applications. If your application supports standard functions, such as refreshing a content-area view or deleting an item, or displays different subsets of data, such as contacts or bookmarks, be sure to use the appropriate system-provided button or icon to represent it. For a complete list of standard buttons and icons, and guidelines on how to use them, see “System-Provided Buttons and Icons.”

尽可能在导航栏、工具栏和标签栏中使用系统自带的按钮和图标。iPhone OS 提供了大量已在内置应用程序中表示用户熟知的标准任务和模式的标准按钮和图标。如果你的应用程序支持这些标准功能，比如刷新内容视图或删除项，或者是显示数据的具体部分，比如联系人或书签，则应当使用恰当的系统内置按钮或图标来表示。关于完整的标签按钮和图标列表及其使用准则，参见“系统自带的按钮与图标”。

Of course, not every task your application performs is a standard one. If your application supports custom tasks users need to perform frequently, you need to create custom icons that represent these tasks in your toolbar or navigation bar. Similarly, if your application displays a tab bar that allows users to switch among custom application modes or custom subsets of data, you need to design tab bar icons that clearly describe these modes or subsets. This section gives you some guidance on how to design icons that work well in navigation bars, toolbars, and tab bars.

当然，不可能你应用程序的每个功能都是标准的。如果你的应用程序提供了用户需要经常执行的特殊任务的话，你就需要创建一个自定义图标以便在工具栏或导航栏中代表那些任务。类似地，如果你的应用程序标签栏上提供了自定义的应用程序模式或者自定义的数据集，你也需要设计标签栏按钮以清晰描述这些模式或数据。本节提供了关于如何为导航栏、工具栏和标签栏设计合适的图标的一些准则。

Before you create the art for your icon, you need to spend some time thinking about what it should convey. As you consider designs, aim for an icon that is:

在进行任何图标设计之前，你需要花点时间来思考它要表达的内容。既然是考虑设计，那么图标应当是：

• Simple and streamlined. Too many details can make an icon appear sloppy or indecipherable.

简明扼要。太多细节会使图标看上去杂乱或者难以理解。

• Not easily mistaken for one of the system-provided icons. Users should be able to distinguish your custom icon from the standard icons at a glance.

不易误认为是某个系统内置的图标。用户应当能够立即区别出你的自定义图标和标准图标。

• Readily understood and widely acceptable. Strive to create a symbol that most users will interpret correctly and that no users will find offensive.

能够迅速理解并得到广泛的认可。力求所创建的符号能够被大部分用户正确理解，且不会使用户感到厌恶。

After you’ve decided on the appearance of your icon, follow these guidelines as you create it:

当你决定了图标的外观后，应在制作时遵循下列准则：

• Use the PNG format.
  使用 PNG 格式。
• Use pure white with appropriate alpha.
  使用具有适当透明的纯白色。
• Do not include a drop shadow.
  不要使用投影。
• Use anti-aliasing.
  使用消除边缘锯齿。
• If you decide to add a bevel, be sure that it is 90° (to help you do this, imagine a light source positioned at the top of the icon).
  如果你希望添加斜边（bevel）效果，应当确保它是 90° 的（想像光是从图标的正上方投射下来的）。
• For toolbar and navigation bar icons, create an icon that measures about 20 x 20 pixels.
  对于工具栏和导航栏图标，其尺寸应约为 20 x 20 像素。

For tab bar icons, create an icon that measures about 30 x 30 pixels.
对于标签栏图标，其尺寸应约为 30 x 30 像素。

iPhone OS automatically provides the pressed or selected appearance for items in navigation bars, toolbars, and tab bars, so you only need to provide a single version of an icon. Because these visual effects are automatic, you cannot change their appearance.

iPhone OS 自动为导航栏、工具栏和标签栏上的项提供按下和选中外观，因此你无须再单独提供。因为这些视觉效果是自动生成的，你无法更改其外观。