What is the file name used by default shared preferences?

Question

Android Backup Service requires a filename to backup shared preferences:

public static final String PREFS = "PrefFile";    
SharedPreferencesBackupHelper helper = new SharedPreferencesBackupHelper(this, PREFS);

It is clear what to use if filename is given during preferences creation like

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

But I use default shared preferences:

SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);

What should I pass as PREFS value to SharedPreferencesBackupHelper?

Ehlke

Answer 1

private static String getDefaultSharedPreferencesName(Context context) {
    return context.getPackageName() + "_preferences";
}

see your package name in AndroidManifest.xml

Bothersome

Is it safe to use hardcoded value _preferences? Will it work properly on all android devices? – Ehlke

It is not guaranteed. So I think it is better to use SP with defined name – Bothersome

Thanks. Is there any method to get the filename from the shared preferences? – Ehlke

This is now exposed as a public method on PreferenceManager in API 24: developer.android.com/reference/android/preference/… – Mundford

LA_ and owner of answer - if there is no public method use Reflections - its better choice as constructing some name from code - which is changing constantly (mean api) - so - down vote for such solutions – Noranorah

Answer 2

From the source code, The PackageName is based on the context that you pass in.

private static String getDefaultSharedPreferencesName(Context context) {
    return context.getPackageName() + "_preferences";
}

Chamois

Unfortunately, the getDefaultSharedPreferencesName method is private. Is there any public method to get it? – Ehlke

Couldn't you just add this method to your code and use it that way? – Chamois

As I've mentioned in the comment to another answer, I am not sure if this is the right way to hardcode it - what will happen if Google changes it in the next Android version? – Ehlke

If you're worried about this changing in the next version why not just use your own key with getSharedPreferences then you won't ever have this issue. developer.android.com/training/basics/data-storage/… – Chamois

Answer 3

The default preference file's name is the calling activity's class name.

https://developer.android.com/reference/android/app/Activity.html#getPreferences(int)

Disobey