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This article introduces how to use SharedPreferences to store objects in Android. The content is very detailed. Interested friends can use it for reference. I hope it will be helpful to you.

Why not use SQLite? For a variety of reasons: except when there is an impedance mismatch between object-oriented and relational databases, SQLite may be overkill (with more overhead) for simple use cases, or its usage and statements may not like it at all. Other Android ORM frameworks (ORMLite, greenDAO, Sugar ORM, ActiveAndroid, etc.) or NOSQL mobile databases, such as Couchbase Lite version (Beta version at this time). Couchbase Lite is basically an JSON database designed to reduce complexity but at the same time violate the law of abstract vulnerabilities (all self-evident abstractions are flawed)

The code is as follows:

/ * * stores the user object in SharedPreferences * / public class UserPrefs {/ * * This application's preferences label * / private static final String PREFS_NAME = "com.our.package.UserPrefs"; / * * This application's preferences * / private static SharedPreferences settings; / * * This application's settings editor*/ private static SharedPreferences.Editor editor / * * Constructor takes an android.content.Context argument*/ public UserPrefs (Context ctx) {if (settings = = null) {settings = ctx.getSharedPreferences (PREFS_NAME, Context.MODE_PRIVATE);} / * Get a SharedPreferences editor instance. * SharedPreferences ensures that updates are atomic * and non-concurrent * / editor = settings.edit ();} /.}

The User code is as follows:

/ * * User object to be saved in db * / public class User {private int id; / / used for object storage private String userName; private boolean registered; private double score; / * * Constructor * / public User (int id, String userName, boolean registered, double score) {this.id = id; this.userName = userName; this.registered = registered; this.score = score;} / / getters and setters here...}

Think of SharedPreferences as a Map store

The CRUD operation is as follows:

/ * * generic field keys * / private static final String KEY_USERNAME = "com.our.package.KEY_USERNAME"; private static final String KEY_REGISTERED = "com.our.package.KEY_REGISTERED"; private static final String KEY_SCORE = "com.our.package.KEY_SCORE"; / * * Store or Update * / public void setUser (User user) {if (user = = null) return; / / don't bother int id = user.getId () Editor.putString (getFieldKey (id, KEY_USERNAME), user.getUsername (); editor.putBoolean (getFieldKey (id, KEY_REGISTERED), user.isRegistered ()); editor.putFloat (getFieldKey (id, KEY_SCORE), user.getScore ()); editor.commit () } / * * Retrieve * / public User getUser (int id) {String name = settings.getString (getFieldKey (id, KEY_USERNAME), ""); / / default value boolean registered = settings.getBoolean (getFieldKey (id, KEY_REGISTERED), false) / default value double score = settings.getFloat (getFieldKey (id, KEY_SCORE), 0); / / default value return new User (id, name, registered, score);} / * * Delete * / public void deleteUser (User user) {if (user = = null) return; / / don't bother int id = user.getId (); editor.remove (getFieldKey (id, KEY_USERNAME)) Editor.remove (getFieldKey (id, KEY_REGISTERED)); editor.remove (getFieldKey (id, KEY_SCORE)); editor.commit ();}

The primary key is through the getFieldKey method, and getFieldKey () gives us a unique identification of each field for each user.

/ * * The prefix for flattened user keys * / public static final String KEY_PREFIX = "com.our.package.KEY"; / * * Method to return a unique key for any field belonging to a given object* @ param id of the object* @ param fieldKey of a particular field belonging to that object* @ return key String uniquely identifying the object's field*/private String getFieldKey (int id, String fieldKey) {return KEY_PREFIX + id + "_" + fieldKey;}

The client calls as follows:

/ / get a SharedPreferences instanceUserPrefs prefs = new UserPrefs (this.getApplicationContext ()); / / get id from server or local storage// then find User with that idUser user = prefs.getUser (id); / / operations on User, e.g.user.setRegistered (true); user.setScore (new_score); / / saveprefs.setUser (user); / /... or deleteprefs.deleteUser (user), Gson

Gson is a Java library that provides simple toJSON () and fromJson () methods to convert Java objects to JSON format and vice versa. We can simply store the entire string in JSON format to SharedPreferences:

/ / convert User object user to JSON formatGson gson = new Gson (); String user_json = gson.toJson (user); / / store in SharedPreferencesString id = "" + user.getId (); / / get storage keyeditor.putString (id, user_json); editor.commit (); / / time flies...// do the reverse operationuser_json = settings.getString (id, "); user = gson.fromJson (user_json, User.class) So much for sharing on how to use SharedPreferences to store objects in Android. I hope the above content can be helpful to you and learn more. If you think the article is good, you can share it for more people to see.

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