使用SharedPreferences在Android存儲對象詳細代碼

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為什麼不用SQLite? 原因多種：除瞭面向對象和關系數據庫之間的阻抗不匹配時，SQLite可能是矯枉過正（帶來瞭更多的開銷）對於一些簡單的用例，或者其用法和語句可能會完全不喜歡。其他Android ORM 框架（ORMLite, greenDAO, Sugar ORM, ActiveAndroid, 等）或NOSQL移動數據庫，如Couchbase精簡版（Beta版在此時間）。 Couchbase精簡版基本上是一個JSON數據庫，它們旨在降低復雜性，但是同時又違背瞭抽象漏洞定律(所有不證自明的抽象都是有漏洞的)

 代碼如下：

/** 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代碼如下：

/** 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...
}

將SharedPreferences看成一個Map存儲，

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();
}

主鍵是通過getFieldKey方法， getFieldKey() 給我們每個用戶每個字段的唯一標識。

/** 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;
}

客戶端調用如下：

// 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),

 Gson

Gson 是一個Java庫，它提供瞭簡單的toJSON（）和fromJson（）方法來轉換Java對象到JSON格式，反之亦然。我們可以簡單地存儲JSON格式整個字符串到SharedPreferences：

 // 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);

到此這篇關於使用SharedPreferences在Android存儲對象詳細代碼的文章就介紹到這瞭,更多相關使用SharedPreferences在Android存儲對象內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet！

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