如何使用SharedPreferences在Android存储对象

这篇文章给大家介绍如何使用SharedPreferences在Android存储对象，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。

为什么不用SQLite? 原因多种：除了面向对象和关系数据库之间的阻抗不匹配时，SQLite可能是矫枉过正（带来了更多的开销）对于一些简单的用例，或者其用法和语句可能会完全不喜欢。其他Android ORM 框架（ORMLite, greenDAO, Sugar ORM, ActiveAndroid, 等）或NOSQL移动数据库，如Couchbase精简版（Beta版在此时间）。 Couchbase精简版基本上是一个JSON数据库，它们旨在降低复杂性，但是同时又违背了抽象漏洞定律(所有不证自明的抽象都是有漏洞的)

代码如下：

/** 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();       }   //...}

其中User代码如下：

/** 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...}

将SharedPreferences看成一个Map存储，

CRUD操作如下：

/** 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();}

主键是通过getFieldKey方法， getFieldKey() 给我们每个用户每个字段的唯一标识。

/** 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;}

客户端调用如下：

// 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 是一个Java库，它提供了简单的toJSON（）和fromJson（）方法来转换Java对象到JSON格式，反之亦然。我们可以简单地存储JSON格式整个字符串到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);

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