If you have a relatively small collection of key-values that you'd like to save,
you can use the SharedPreferences
APIs. A SharedPreferences
object
points to a file containing key-value pairs and provides simple methods to read
and write them. Each SharedPreferences
file is managed by the framework and
can be private or shared.
This page shows you how to use the SharedPreferences
APIs to store and
retrieve simple values.
Get a handle to shared preferences
You can create a new shared preference file or access an existing one by calling one of these methods:
getSharedPreferences()
: Use this if you need multiple shared preference files identified by name, which you specify with the first parameter. You can call this from anyContext
in your app.getPreferences()
: Use this from anActivity
if you need to use only one shared preference file for the activity. Because this retrieves a default shared preference file that belongs to the activity, you don't need to supply a name.
For example, the following code accesses the shared preferences file that's
identified by the resource string R.string.preference_file_key
and opens it
using the private mode so the file is accessible by only your app:
Kotlin
val sharedPref = activity?.getSharedPreferences( getString(R.string.preference_file_key), Context.MODE_PRIVATE)
Java
Context context = getActivity(); SharedPreferences sharedPref = context.getSharedPreferences( getString(R.string.preference_file_key), Context.MODE_PRIVATE);
When naming your shared preference files, you should use a name that's uniquely
identifiable to your app. A good way to do this is prefix the file name with
your application ID. For example:
"com.example.myapp.PREFERENCE_FILE_KEY"
Alternatively, if you need just one shared preference file for your activity,
you can use the getPreferences()
method:
Kotlin
val sharedPref = activity?.getPreferences(Context.MODE_PRIVATE)
Java
SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE);
If you're using the SharedPreferences
API to save app settings, you
should instead use getDefaultSharedPreferences()
to get the default
shared preference file for your entire app. For more information, see the
Settings developer guide.
Write to shared preferences
To write to a shared preferences file, create a SharedPreferences.Editor
by calling edit()
on your SharedPreferences
.
Pass the keys and values you want to write with methods such as:
putInt()
andputString()
. Then call apply()
or
commit()
to save the changes. For example:
Kotlin
val sharedPref = activity?.getPreferences(Context.MODE_PRIVATE) ?: return with (sharedPref.edit()) { putInt(getString(R.string.saved_high_score_key), newHighScore) apply() }
Java
SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE); SharedPreferences.Editor editor = sharedPref.edit(); editor.putInt(getString(R.string.saved_high_score_key), newHighScore); editor.apply();
apply()
changes the in-memory SharedPreferences
object immediately but
writes the updates to disk asynchronously. Alternatively, you can use commit()
to write the data to disk synchronously. But because commit()
is synchronous,
you should avoid calling it from your main thread because it could pause your UI
rendering.
Read from shared preferences
To retrieve values from a shared preferences file, call methods such as
getInt()
and getString()
, providing the key for the value you
want, and optionally a default value to return if the key isn't present. For
example:
Kotlin
val sharedPref = activity?.getPreferences(Context.MODE_PRIVATE) ?: return val defaultValue = resources.getInteger(R.integer.saved_high_score_default_key) val highScore = sharedPref.getInt(getString(R.string.saved_high_score_key), defaultValue)
Java
SharedPreferences sharedPref = getActivity().getPreferences(Context.MODE_PRIVATE); int defaultValue = getResources().getInteger(R.integer.saved_high_score_default_key); int highScore = sharedPref.getInt(getString(R.string.saved_high_score_key), defaultValue);