Mark Murphy - Beginning Android

menu. add(Menu.NONE, EDIT_ID, Menu.NONE, "Edit Prefs")

. setIcon(R.drawable.misc)

. setAlphabeticShortcut('e');

menu. add(Menu.NONE, CLOSE_ID, Menu.NONE, "Close")

. setIcon(R.drawable.eject)

. setAlphabeticShortcut('c');

return( super. onCreateOptionsMenu(menu));

}

@Override

publicboolean onOptionsItemSelected(MenuItem item) {

switch(item. getItemId()) {

caseEDIT_ID:

startActivity( new Intent( this, EditPreferences. class));

return( true);

caseCLOSE_ID:

finish();

return( true);

}

return( super. onOptionsItemSelected(item));

}

However, that is all that is needed, and it really is not that much code outside of the preferences XML. What you get for your effort is an Android-supplied preference UI, as shown in Figure 17-1.

Figure 17-1. The Simple project’s preferences UI

The checkbox can be directly checked or unchecked. To change the ringtone preference, just click on the entry in the preference list to bring up a selection dialog like the one in Figure 17-2.

Figure 17-2. Choosing a ringtone preference

Note that there is no explicit Save or Commit button or menu — changes are persisted as soon as they are made.

The SimplePrefsDemoactivity, beyond having the aforementioned menu, also displays the current preferences via a TableLayout:

xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

>

android:text="Checkbox:"

android:paddingRight="5px"

/>

/>

android:text="Ringtone:"

android:paddingRight="5px"

/>

/>

The fields for the table are found in onCreate():

@Override

publicvoid onCreate(Bundle savedInstanceState) {

super. onCreate(savedInstanceState);

setContentView(R.layout.main);

checkbox = (TextView) findViewById(R.id.checkbox);

ringtone = (TextView) findViewById(R.id.ringtone);

}

The fields are updated on each onResume():

@Override

publicvoid onResume() {

super. onResume();

SharedPreferences prefs = PreferenceManager

. getDefaultSharedPreferences( this);

checkbox. setText( new Boolean(prefs

. getBoolean("checkbox", false)). toString());

ringtone. setText(prefs. getString("ringtone", ""));

}

This means the fields will be updated when the activity is opened and after the preferences activity is left (e.g., via the back button); see Figure 17-3.

Figure 17-3. The Simple project’s list of saved preferences

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.

Categories are added via a PreferenceCategoryelement 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 PreferenceCategoryelements 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 PreferenceScreenelement.

Yes, that PreferenceScreenelement.

Any children of PreferenceScreengo 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, from the Prefs/Structuredsample project on the Apress Web site, here is a preference XML file that contains both PreferenceCategoryand nested PreferenceScreenelements:

xmlns:android="http://schemas.android.com/apk/res/android">

android:key="@string/checkbox"

android:title="Checkbox Preference"

android:summary="Check it on, check it off"

/>

android:key="@string/ringtone"

android:title="Ringtone Preference"

android:showDefault="true"

android:showSilent="true"

android:summary="Pick a tone, any tone"

/>

android:key="detail"

android:title="Detail Screen"

android:summary="Additional preferences held in another page">

android:key="@string/checkbox2"

android:title="Another Checkbox"

android:summary="On. Off. It really doesn't matter."

/>

The result, when you use this preference XML with your PreferenceActivityimplementation, is a categorized list of elements like those in Figure 17-4.

Figure 17-4. The Structured project’s preference UI, showing categories and a screen placeholder

And if you tap on the Detail Screen entry, you are taken to the child preference screen (Figure 17-5).

Figure 17-5. The child preference screen of the Structured project’s preference UI