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CHAPTER 21: Using Preferences
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Figure 21–3. The Simple project's list of saved preferences
Adding a Wee Bit o' Structure
If you have a lot of preferences for users to set, putting them all in one big list may not
be the best idea. Android’s preference framework gives you a few ways to impose a bit
of structure on your bag of preferences, including categories and screens.
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 place 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 a whole lot of preferences—more than are convenient for users to scroll
through—you can also put them on separate “screens” by introducing the
PreferenceScreen element. Yes, that 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, and
tapping that entry brings up the child screen.
For example, from the Prefs/Structured sample project, here is a preference XML file
that contains both PreferenceCategory and nested PreferenceScreen elements:
<PreferenceScreen
xmlns:android="
<PreferenceCategory android:title="Simple Preferences">
<CheckBoxPreference
android:key="checkbox"
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android:title="Checkbox Preference"
android:summary="Check it on, check it off"
/>
<RingtonePreference
android:key="ringtone"
android:title="Ringtone Preference"
android:showDefault="true"
android:showSilent="true"
android:summary="Pick a tone, any tone"
/>
</PreferenceCategory>
<PreferenceCategory android:title="Detail Screens">
<PreferenceScreen
android:key="detail"
android:title="Detail Screen"
android:summary="Additional preferences held in another page">
<CheckBoxPreference
android:key="checkbox2"
android:title="Another Checkbox"
android:summary="On. Off. It really doesn't matter."
/>
</PreferenceScreen>
</PreferenceCategory>
</PreferenceScreen>
The result, when you use this preference XML with your PreferenceActivity
implementation, is a categorized list of elements, as shown in Figure 21–4.
Figure 21–4. The Structured project's preference UI, showing categories and a screen placeholder
If you tap the Detail Screen entry, you are taken to the child preference screen, as
shown in Figure 21–5.
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Figure 21–5. The child preference screen of the Structured project's preference UI
The Kind of Pop-Ups You Like
Of course, not all preferences are check boxes and ringtones. For others, like entry
fields and lists, Android uses pop-up dialogs. Users do not enter their preference
directly in the preference UI activity, but rather tap a preference, fill in a value, and click
OK to commit the change.
Structurally, in the preference XML, fields and lists are not significantly different from
other preference types, as seen in this preference XML from the Prefs/Dialogs
sample project:
<PreferenceScreen
xmlns:android="
<PreferenceCategory android:title="Simple Preferences">
<CheckBoxPreference
android:key="checkbox"
android:title="Checkbox Preference"
android:summary="Check it on, check it off"
/>
<RingtonePreference
android:key="ringtone"
android:title="Ringtone Preference"
android:showDefault="true"
android:showSilent="true"
android:summary="Pick a tone, any tone"
/>
</PreferenceCategory>
<PreferenceCategory android:title="Detail Screens">
<PreferenceScreen
android:key="detail"
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android:title="Detail Screen"
android:summary="Additional preferences held in another page">
<CheckBoxPreference
android:key="checkbox2"
android:title="Another Checkbox"
android:summary="On. Off. It really doesn't matter."
/>
</PreferenceScreen>
</PreferenceCategory>
<PreferenceCategory android:title="Simple Preferences">
<EditTextPreference
android:key="text"
android:title="Text Entry Dialog"
android:summary="Click to pop up a field for entry"
android:dialogTitle="Enter something useful"
/>
<ListPreference
android:key="list"
android:title="Selection Dialog"
android:summary="Click to pop up a list to choose from"
android:entries="@array/cities"
android:entryValues="@array/airport_codes"
android:dialogTitle="Choose a Pennsylvania city" />
</PreferenceCategory>
</PreferenceScreen>
With the field (EditTextPreference), in addition to the title and summary you put on the
preference itself, you can also supply the title to use for the dialog.
With the list (ListPreference), you supply both a dialog title and two string-array
resources: one for the display names and one for the values. These need to be in the
same order, because the index of the chosen display name determines which value is
stored as the preference in the SharedPreferences. For example, here are the arrays for
use by the ListPreference shown in the preceding example:
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string-array name="cities">
<item>Philadelphia</item>
<item>Pittsburgh</item>
<item>Allentown/Bethlehem</item>
<item>Erie</item>
<item>Reading</item>
<item>Scranton</item>
<item>Lancaster</item>
<item>Altoona</item>
<item>Harrisburg</item>
</string-array>
<string-array name="airport_codes">
<item>PHL</item>
<item>PIT</item>
<item>ABE</item>
<item>ERI</item>
<item>RDG</item>
<item>AVP</item>
<item>LNS</item>
<item>AOO</item>
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<item>MDT</item>
</string-array>
</resources>
When you bring up the preference UI, you start with another category with another pair
of preference entries, as shown in Figure 21–6.
Figure 21–6. The preference screen of the Dialogs project's preference UI
Tapping the Text Entry Dialog entry brings up a text-entry dialog with the prior
preference entry already filled in, as shown in Figure 21–7.
Figure 21–7. Editing a text preference
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Tapping Selection Dialog brings up a selection dialog showing the display names from
the one array, as shown in Figure 21–8.
Figure 21–8. Editing a list preference
