Difference between getDefaultSharedPreferences and

问题:

What is the difference between getDefaultSharedPreferences and getSharedPreferences in Android? Can anyone please explain?

回答1:

getDefaultSharedPreferences will use a default name like \"com.example.something_preferences\", but getSharedPreferences will require a name.

getDefaultSharedPreferences in fact uses Context.getSharedPreferences (below is directly from the Android source):

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

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

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

回答2:

Let\'s review the basic points of difference:

1. getDefaultSharedPreferences() uses a default preference-file name. This default is set per application, so all activities in the same app context can access it easily as in the following example:

   SharedPreferences spref = PreferenceManager.getDefaultSharedPreferences(this);
   if (spref.contains(\"email\")) {
        String sEmailAddr = spref.getString(\"email\", \"\");
   }
   

   The preferences are usually stored at /data/data/com.package.name/shared_prefs/com.package.name_preferences.xml.

2. The alternative method - getSharedPreferences(name,mode) requires to indicate a specific preference (file) name and an operation mode (e.g. private, world_readable, etc.)

As mentioned by copolii, the result is the same, but the first option is simpler and lacks the flexibility to split to multiple preference files, that is offered by the second option of getSharedPreferences(). Sharing the preferences between apps using a MODE_WORLD_READABLE operation indicator is also something possible using getSharedPreferences(), but is rarely used.

IMHO, getDefaultSharedPreferences() can be safely used without going into the confusion of multiple preference file names that are prone to typos and confusion, unless you want that different modules in your app will use different preference files. Normally this is not needed. If an app needs to save a lot of parameters, probably using external database will be better as it offers also better data protection.

If someone knows of a good reason to regularly use getSharedPreferences() and not getDefaultSharedPreferences(), please let me know by commenting here.

回答3:

There\'s a 3rd function as well:

public SharedPreferences Activity.getPreferences(int mode) {}

See my question and answer here: Mess with the shared preferences of android - which function to use?

回答4:

Both getSharedPreferences() and getDefaultSharedPreferences() are used to access application-level preferences .getDefaultSharedPreferences() is used to get the shared preferences that work in accordance with Android’s overall preference framework. getDefaultSharedPreferences() is better to use as it gives the SharedPreferences object that works with a PreferenceActivity by default.

回答5:

I know this post is a bit old, but since 24.0.1 of the v7 support library you can retrieve the default preferences by context anywhere using

// context might be an application context, activity, ..
// so if you want to get your apps defaults, pass an activity context
PreferenceManager.getDefaultSharedPreferences(context)

See https://developer.android.com/reference/android/support/v7/preference/PreferenceManager#getdefaultsharedpreferences