使用SharedPreferences在Android存储对象详细代码

public class UserPrefs{

    
    private static final String PREFS_NAME = "com.our.package.UserPrefs";


 
    
    private static SharedPreferences settings;

   
   private static SharedPreferences.Editor editor;


 
   
   public UserPrefs(Context ctx){
        if(settings == null){
           settings = ctx.getSharedPreferences(PREFS_NAME,
                                               Context.MODE_PRIVATE );
        }
       
        editor = settings.edit();    
   }
   //...
}

public class User{

    private int id; // used for object storage
    private String userName;
    private boolean reGIStered;
    private double score;


 
    
   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...
}

 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";


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();
}


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);
}


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();
}

public static final String KEY_PREFIX =
            "com.our.package.KEY";


private String getFieldKey(int id, String fieldKey) {
       return  KEY_PREFIX + id + "_" + fieldKey;
}

// get a SharedPreferences instance
UserPrefs prefs = new UserPrefs( this.getApplicationContext() );

// get id from server or local storage
// then find User with that id
User user = prefs.getUser(id);

// operations on User, e.g.
user.setRegistered(true);
user.setScore(new_score);

// save
prefs.setUser(user);
// ...or delete
prefs.deleteUser(user),

 // convert User object user to JSON format
Gson gson = new Gson();
String user_json = gson.toJson(user);

// store in SharedPreferences
String id = "" + user.getId(); // get storage key
editor.putString(id, user_json);
editor.commit();

// time flies...

// do the reverse operation
user_json = settings.getString(id, "");
user = gson.fromJson(user_json, User.class);