In a previous post, we covered the basics of the new preference system in Android. To recap: you can define preference characteristics in an XML file. This in turn gives you an Android-generated preference screen, which you can launch from an activity. The results are stored in the SharedPreferences for your application for later retrieval. Today, we will continue our look at the preferences UI, in an excerpt from The Busy Coderâ€™s Guide to Android Development.
If you have a lot of preferences for users to set, having them all in one big list may become troublesome. Android’s preference framework gives you a few ways to impose a bit of structure on your bag of preferences, including categories and screens.
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Categories are added via a PreferenceCategory element in your preference XML and are used to group together related preferences. Rather than have your preferences all as children of the root PreferenceScreen, you can put a few PreferenceCategory elements in the PreferenceScreen, and then put your preferences in their appropriate categories. Visually, this adds a divider with the category title between groups of preferences.
If you have lots and lots of preferences — more than is convenient for users to scroll through — you can also put them on separate “screens” by introducing the PreferenceScreen element.
Any children of PreferenceScreen go on their own screen. If you nest PreferenceScreens, the parent screen displays the screen as a placeholder entry — tapping that entry brings up the child screen.
For example, here is a preference XML file that contains both PreferenceCategory and nested PreferenceScreen elements:
The result, when you use this preference XML with your PreferenceActivity implementation, is a categorized list of elements:
And, if you tap on the Detail Screen entry, you are taken to the child preference screen:
Next time, in the third and final(?) part of this series of blog posts, we will look at elements that support free-form text entry or a selection of an item out of a list.