CELLINK Constant support for the UI, embedded firmware, connectivity, and other software-related features of bioprinting products by CELLINK, the world’s leading biotech company
CELLINK Constant support for the UI, embedded firmware, connectivity, and other software-related features of bioprinting products by CELLINK, the world’s leading biotech company
Best Practice: SharedPreferences Android provides many ways of storing application data. One of these ways leads us to the SharedPreferences object which is used to store private primitive data in key-value pairs. All logic is based on three simple classes only: SharedPreferences SharedPreferences.Editor SharedPreferences.OnSharedPreferenceChangeListener SharedPreferences SharedPreferences is main of them. It's responsible for getting (parsing) stored data, provides interface for getting Editor object and interfaces for adding and removing OnSharedPreferenceChangeListener To create SharedPreferences you will need Context object (can be an application Context) getSharedPreferences method parses Preference file and creates Map object for it You can create it in few modes provided by Context, it's strongly recommended to use MODE_PRIVATE because creating world-readable/writable files is very dangerous, and likely to cause security holes in applications Show code // parse Preference file SharedPreferences preferences = context.getSharedPreferences("com.example.app", Context.MODE_PRIVATE); // get values from Map preferences.getBoolean("key", defaultValue) preferences.get..("key", defaultValue) // you can get all Map but be careful you must not modify the collection returned by this // method, or alter any of its contents. Map<String, ?> all = preferences.getAll(); // get Editor object SharedPreferences.Editor editor = preferences.edit(); //add on Change Listener preferences.registerOnSharedPreferenceChangeListener(mListener); //remove on Change Listener preferences.unregisterOnSharedPreferenceChangeListener(mListener); // listener example SharedPreferences.OnSharedPreferenceChangeListener mOnSharedPreferenceChangeListener = new SharedPreferences.OnSharedPreferenceChangeListener() { @Override public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) { } }; Editor SharedPreferences.Editor is an Interface used for modifying values in a SharedPreferences object. All changes you make in an editor are batched, and not copied back to the original SharedPreferences until you call commit() or apply() Use simple interface to put values in Editor Save values synchronous with commit() or asynchronous with apply which is faster. In fact of using different threads using commit() is safer. Thats why I prefer to use commit(). Remove single value with remove() or clear all values with clear() Show code // get Editor object SharedPreferences.Editor editor = preferences.edit(); // put values in editor editor.putBoolean("key", value); editor.put..("key", value); // remove single value by key editor.remove("key"); // remove all values editor.clear(); // commit your putted values to the SharedPreferences object synchronously // returns true if success boolean result = editor.commit(); // do the same as commit() but asynchronously (faster but not safely) // returns nothing editor.apply(); Performance & Tips SharedPreferences is a Singleton object so you can easily get as many references as you want, it opens file only when you call getSharedPreferences first time, or create only one reference for it. Show code // There are 1000 String values in preferences SharedPreferences first = context.getSharedPreferences("com.example.app", Context.MODE_PRIVATE); // call time = 4 milliseconds SharedPreferences second = context.getSharedPreferences("com.example.app", Context.MODE_PRIVATE); // call time = 0 milliseconds SharedPreferences third = context.getSharedPreferences("com.example.app", Context.MODE_PRIVATE); // call time = 0 milliseconds As SharedPreferences is a Singleton object you can change any of It's instances and not be scared that their data will be different Show code first.edit().putInt("key",15).commit(); int firstValue = first.getInt("key",0)); // firstValue is 15 int secondValue = second.getInt("key",0)); // secondValue is also 15 When you call get method first time it parses value by key and adds this value to the map. So for second call it just gets it from map, without parsing. Show code first.getString("key", null) // call time = 147 milliseconds first.getString("key", null) // call time = 0 milliseconds second.getString("key", null) // call time = 0 milliseconds third.getString("key", null) // call time = 0 milliseconds Remember the larger the Preference object is the longer get, commit, apply, remove and clear operations will be. So it's highly recommended to separate your data in different small objects. Your Preferences will not be removed after Application update. So there are cases when you need to create some migration scheme. For example you have Application that parse local JSON in start of application, to do this only after first start you decided to save boolean flag wasLocalDataLoaded. After some time you updated that JSON and released new application version. Users will update their applications but they will not load new JSON because they already done it in first application version. Show code public class MigrationManager { private final static String KEY_PREFERENCES_VERSION = "key_preferences_version"; private final static int PREFERENCES_VERSION = 2; public static void migrate(Context context) { SharedPreferences preferences = context.getSharedPreferences("pref", Context.MODE_PRIVATE); checkPreferences(preferences); } private static void checkPreferences(SharedPreferences thePreferences) { final double oldVersion = thePreferences.getInt(KEY_PREFERENCES_VERSION, 1); if (oldVersion < PREFERENCES_VERSION) { final SharedPreferences.Editor edit = thePreferences.edit(); edit.clear(); edit.putInt(KEY_PREFERENCES_VERSION, currentVersion); edit.commit(); } } } SharedPreferences are stored in an xml file in the app data folder Show code // yours preferences /data/data/YOUR_PACKAGE_NAME/shared_prefs/YOUR_PREFS_NAME.xml // default preferences /data/data/YOUR_PACKAGE_NAME/shared_prefs/YOUR_PACKAGE_NAME_preferences.xml Android guide. Sample Code Show code public class PreferencesManager { private static final String PREF_NAME = "com.example.app.PREF_NAME"; private static final String KEY_VALUE = "com.example.app.KEY_VALUE"; private static PreferencesManager sInstance; private final SharedPreferences mPref; private PreferencesManager(Context context) { mPref = context.getSharedPreferences(PREF_NAME, Context.MODE_PRIVATE); } public static synchronized void initializeInstance(Context context) { if (sInstance == null) { sInstance = new PreferencesManager(context); } } public static synchronized PreferencesManager getInstance() { if (sInstance == null) { throw new IllegalStateException(PreferencesManager.class.getSimpleName() + " is not initialized, call initializeInstance(..) method first."); } return sInstance; } public void setValue(long value) { mPref.edit() .putLong(KEY_VALUE, value) .commit(); } public long getValue() { return mPref.getLong(KEY_VALUE, 0); } public void remove(String key) { mPref.edit() .remove(key) .commit(); } public boolean clear() { return mPref.edit() .clear() .commit(); } }