What's the difference between getDefaultSharedPreferences() and getPreferences()?

Question

I'm currently taking the "Developing Android Apps" Udacity course. In the "Lesson 3: New Activities and Intents > Use SharedPreferences" segment, the instructor asked me to dig around the Android Developer site for how to get the user preferences from SharedPreferences. However, I found it different between the official documentation and the course's solution.

The Udacity course's solution says, to grab a SharedPreferences instance for the PreferenceActivity, you should call:

SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getActivity());

(where getActivity() is simply the Context here because it's called inside a Fragment.)

While the official documentation on Android Developer Site indicates that you should call:

SharedPreferences prefs = getActivity().getPreferences(Context.MODE_PRIVATE)

So what's the difference between PreferenceManager.getDefaultSharedPreferences(Context context) and Activity.getPreferences(int mode)?

Please note: This question does not involve anything about getSharedPreferences() which requires a file name. It's about the difference between getPreferences() and getDefaultSharedPreferences().

Thanks in advance.

Maser

Answer 1

Acoording to the link you provided to Android documentation

getSharedPreferences() - Use this if you need multiple preferences files identified by name, which you specify with the first parameter.

getPreferences() - Use this if you need only one preferences file for your Activity. Because this will be the only preferences file for your Activity, you don't supply a name.

So it is, use getSharedPreferences when the data you want to save/retrieve can be used from different activities in the app. If those preferences will only be used in one Activity, you can use getPreferences.

Edit: also note that as said in the post you linked 'getDefaultSharedPreferences will use a default name like "com.example.something_preferences", but getSharedPreferences will require a name'

Gabriello

the question did not address getsharedprefereces... it was about the differences between getdefaultsharedpreference and getpreferences... also note that if a preference key/value is stored using getshared preferences or getpreferences it will not be available as a default preference in another activity... you know like the question asked about the differences between the things you didn't address... – Coaly

Answer 2

One of the major differences: getPreferences () returns a file only related to the activity it is opened from. While getDefaultSharedPreferences () returns the application's global preferences. Learned that the hard way yesterday.

Coaly

Here you can find the relevant documentation: developer.android.com/guide/topics/ui/… – Jaella

If I understand you correctly, calling getPreferences() in two different activities will result in two different files, right? – Jorgenson

Answer 3

If you take a look inside PreferenceManager:

public static SharedPreferences getDefaultSharedPreferences(Context context) {
    return context.getSharedPreferences(getDefaultSharedPreferencesName(context),
            getDefaultSharedPreferencesMode());
}

/**
 * Returns the name used for storing default shared preferences.
 *
 * @see #getDefaultSharedPreferences(Context)
 * @see Context#getSharedPreferencesPath(String)
 */
public static String getDefaultSharedPreferencesName(Context context) {
    return context.getPackageName() + "_preferences";
}

private static int getDefaultSharedPreferencesMode() {
    return Context.MODE_PRIVATE;
}

So getDefaultSharedPreferences() use getSharedPreferences() method with your app package name and mode private, if you use getPreferences() from activity it will use the same getSharedPreferences() method but with getLocalClassName();

Alage

Answer 4

From the first article linked below: "Note: The SharedPreferences APIs are only for reading and writing key-value pairs and you should not confuse them with the Preference APIs, which help you build a user interface for your app settings (although they use SharedPreferences as their implementation to save the app settings)."

http://developer.android.com/training/basics/data-storage/shared-preferences.html

http://developer.android.com/guide/topics/ui/settings.html

Lys