User preferences file vs App preferences file

Question

My android application has two kinds of preferences:

1) I have user preferences defined in res/xml/preferences.xml so that users can manage their preferences with a PreferenceActivity.

2) I'd like to define another file for global configuration preferences of my app.

What is the best way to manage my app config preferences? Should I create another XML file with config values or should I specify those config values in strings.xml? What is the best practice for managing config preferences?

Answer 1

Preference files are not storead in project's /res/xml/defaults.xml

They are stored on the device in your application folder something like

/data/data/com.your.pkg/default.prefs

Try do not specify the file name, as you will have some problems with the preference files, like this OP had in this question: How do I get preferences to work in Android?

SharedPreferences preferences = PreferenceManager
                    .getDefaultSharedPreferences(context);

Then you will probably have to query

preferences.getString('weightPref', null);

Many applications may provide a way to capture user preferences on the settings of a specific application or an activity. For supporting this, Android provides a simple set of APIs.

Preferences are typically name value pairs. They can be stored as “Shared Preferences” across various activities in an application (note currently it cannot be shared across processes). Or it can be something that needs to be stored specific to an activity.

1. Shared Preferences: The shared preferences can be used by all the components (activities, services etc) off the applications.

2. Activity handled preferences: These preferences can only be used with in the activity and can not be used by other components of the application.

Shared Preferences:

The shared preferences are managed with the help of getSharedPreferences method of the Context class. The preferences are stored in a default file(1) or you can specify a file name(2) to be used to refer to the preferences.

(1) Here is how you get the instance when you specify the file name

public static final String PREF_FILE_NAME = "PrefFile";
   SharedPreferences preferences = getSharedPreferences(PREF_FILE_NAME, MODE_PRIVATE);

MODE_PRIVATE is the operating mode for the preferences. It is the default mode and means the created file will be accessed by only the calling application. Other two mode supported are MODE_WORLD_READABLE and MODE_WORLD_WRITEABLE. In MODE_WORLD_READABLE other application can read the created file but can not modify it. In case of MODE_WORLD_WRITEABLE other applications also have write permissions for the created file.

(2) The recommended way is to use by the default mode, without specifying the file name

SharedPreferences preferences = PreferencesManager.getDefaultSharedPreferences(context);

Finally, once you have the preferences instance, here is how you can retrieve the stored values from the preferences:

 int storedPreference = preferences.getInt("storedInt", 0);

To store values in the preference file SharedPreference.Editor object has to be used. Editor is the nested interface of the SharedPreference class.

SharedPreferences.Editor editor = preferences.edit();
editor.putInt("storedInt", storedPreference); // value to store
editor.commit();

Editor also support methods like remove() and clear() to delete the preference value from the file.

Activity Preferences:

The shared preferences can be used by other application components. But if you do not need to share the preferences with other components and want to have activities private preferences. You can do that with the help of getPreferences() method of the activity. The getPreference method uses the getSharedPreferences() method with the name of the activity class for the preference file name.

Following is the code to get preferences

SharedPreferences preferences = getPreferences(MODE_PRIVATE);
int storedPreference = preferences.getInt("storedInt", 0);

The code to store values is also same as in case of shared preferences.

SharedPreferences preferences = getPreference(MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putInt("storedInt", storedPreference); // value to store
editor.commit();

You can also use other methods like storing the activity state in database. Note Android also contains a package called android.preference. The package defines classes to implement application preferences UI.

To see some more examples check Android's Data Storage post on developers site.

Answer 2

Let us assume that your xml reads like this:

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"&gt;
   <CheckBoxPreference android:key="gpsOn" 
                    android:summaryOff="GPS is Off"
                    android:summaryOn="GPS is On" 
                    android:title="GPS State"></CheckBoxPreference>

I assume you use a PreferenceActivity to load the preferences from your xml. So in your activity you do addPreferencesFromResource(R.xml.application_pref);

When you do this, by default, all the values are stored in the default SharedPreference of the application. You can access these preferences in anywhere you want. So from some other activity/service just do:

SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getBaseContext());
boolean value = prefs.getBoolean("gpsOn", false);

And just like that you should get the user's preference in value.

Answer 3

Probably the best way to set global configuration preferences for an app is to define meta-data elements in the Android Manifest