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页面指示器

Page Indicators

A page indicator displays a dot for each currently open view in an application. From left to right, the dots represent the order in which the views were opened (the leftmost dot represents the first view). The currently visible view is indicated by a glow on the dot that represents it. Users tap to the left or the right of the glowing dot to view the previous or next open view. Figure 9-6 shows an example of a page indicator.

页面指示器会显示为一个小点在一个应用中，从左到右，小点代表了被打开视图的顺序（最左边的小点代表第一个视图），用一个白色的亮点代表当前视图，用户点击亮点的左边或者右边，可以查看前一个或者后一个视图。图9-6展示了一个页面指示器的例子。

Figure 9-6  A page indicator
图9-6　一个页面指示器

A page indicator gives users a quick way to see how many views are open and an indication of the order in which they were opened; it does not help users keep track of the steps they took through a hierarchy of views. Because the views in a utility application tend to be peers of each other, a page indicator is sufficient to help users navigate through them. A productivity application that displays hierarchical information, on the other hand, should offer navigation through the elements in the navigation bar (for more on this, see “Navigation Bars”).

页面指示器可以使用户清楚的了解当前已打开视图的数量及其排列的顺序，但它不会记录视图的层次结构。因为utility application的视图通常对等出现，页面指示器便足以的帮助用户浏览它们。另一方面，一个显示层级信息的productivity application应该通过导航栏中的元素为用户提供导航（可参考“Navigation Bars”）。

Typically, page indicators work well near the bottom edge of the application screen, below the views it contains. This leaves the more important information (the view itself) in the upper part of the screen where users can see it easily. Be sure to vertically center a page indicator between the bottom edge of the view and the bottom edge of the screen.

通常情况下，页面指示器应该放在应用屏幕的底端，界面视图的下面。这样可以让用户很容易的看到屏幕上面较重要的信息。页面指示应垂直居中于视图底脚空白和屏幕底角空白之间。

Although there is no programmatic limit to the number of dots you can display in a page indicator, be aware that the dots do not shrink or squeeze together as more appear. For example, in portrait orientation, you can display at most 20 dots in a page indicator before clipping occurs. Therefore, you should provide logic in your application to avoid this situation.

虽然对页面指示器中指示点的数量没有明确的限制，但是当界面越来越多的时候，注意指示点之间不能过于密集。例如，在直式定向中，未剪辑前最多指示20个页面。因此，你的应用程序应该有一定的逻辑以免发生类似情况。

Although you can hide a page indicator when there is only one open view, the default behavior is to display it.

尽管在当前只有一页的时候，页面指示器可以隐藏，但默认状态是显示它。

To learn more about using a page indicator in your code, see UIPageControl Class Reference.

了解更多关于在代码中使用页面指示器的内容，请参考UIPageControl Class Reference。