使用Blackberry平台的永久存储-PersistentStore

来源：互联网发布：圣元淘宝网折800 编辑：程序博客网时间：2024/05/10 03:32

Blackberry SDK 5.0 版本支持三种存储方式：

RMS - Record Store
PersistentStore - persistent store for RIMlet
SQL Lite for RIMlet

RMS方式的存储是基于byte数组的存储，对象需要先序列化，再存储。SQL Lite是数据库方式存储，支持SQL语句，这是5.0 SDK的新特性。Blackberry最成熟，最流行的存储方式是PersistentStore，可以直接存储对象。本文详细介绍PersistentStore的方式。

PersistentStore存储对数据类型和对象的要求：

被存储对象只包含基本数据类型 - int, String, long, boolean, byte, 等等
被存储类必须要执行 Persistable 接口

PersistentStore以Key-Value pair的方式进行数据存储，key必须是一个long值，value的类型是Object. 下面来看一个例子：

1. 创建存储数据类，比如class MyData:

public class MyData implements Persistable{

private String m_userName;
private String m_company;
private String m_title;
private int m_age;

public MyData(){}

public void setUserName(String userName){
  m_userName = userName;
}

public String getUserName(){
  return m_userName;
}

public void setCompany(String company){
  m_company = company;
}

public String getCompany(){
  return m_company;
}

public void setTitle(String title){
  m_title = title;
}

public String getTitle(){
  return m_title;
}

public void setAge(int age){
  m_age = age;
}

public int getAge(){
  return m_age;
}

}

注意的是MyData类执行了Persistable接口，这个接口没有任何要执行的函数。MyData的instance variable都是基本类型，也可以有方法。

2. 存储数据

public static final long ID = 0x5d8a91784555e0f8L;

public void saveData(){

  if (myData == null){
   myData = new MyData();
  }

  myData.setUserName("Protoss");
  myData.setCompany("Blizzard");
  myData.setTitle("Manager");
  myData.setAge(26);

  if (dataStore == null){
   dataStore = PersistentStore.getPersistentObject(ID);
  }

  synchronized(dataStore){
   if (dataStore.getContents() == null){
    dataStore.setContents(myData);
    dataStore.commit();
   }
  }
}

PersistentStore是key-value pair的存储，需要一个ID，对应一个PersistentObject，存取数据时都要用到，一个ID只对应一个PersistentObject。存储第一步需要从PersistentStore中用ID获取PersistentObject，再调用PersistentObject.setContents(Object)接口填入存储对象，这步其实还没有保存数据，需要调用PersistentObject.commit()保存数据。

3. 获取数据

public static final long ID = 0x5d8a91784555e0f8L;

public void recoverDataFromStore(){

  if (dataStore == null){
   dataStore = PersistentStore.getPersistentObject(ID);
  }

  synchronized(dataStore){

   if (dataStore.getContents() != null){
    myData = (MyData) dataStore.getContents();
   }
  }

  if (myData != null){
   userNameField.setText(myData.getUserName());
   companyField.setText(myData.getCompany());
   titleField.setText(myData.getTitle());
   ageField.setText(myData.getAge()+"");
  }
}

获取数据第一步用ID获取对应的持久对象PersistentObject，在调用PersistentObject.getContents()获取数据对象，获取的对象类为Object，需要转换成实际的类型，比如 myData = (MyData) dataStore.getContents()。

如下是PersistentStore的完整例子代码，可以拷贝到Eclipse里运行：

import net.rim.device.api.ui.UiApplication;

public class MyApp extends UiApplication{

public static void main(String[] args){
  MyApp app = new MyApp();
  app.enterEventDispatcher();
}

public MyApp(){
  MyScreen myScreen = new MyScreen();
  pushScreen(myScreen);
}
}

import net.rim.device.api.util.Persistable;

public class MyData implements Persistable{

import net.rim.device.api.system.PersistentObject;
import net.rim.device.api.system.PersistentStore;
import net.rim.device.api.ui.Field;
import net.rim.device.api.ui.FieldChangeListener;
import net.rim.device.api.ui.component.BasicEditField;
import net.rim.device.api.ui.component.ButtonField;
import net.rim.device.api.ui.component.LabelField;
import net.rim.device.api.ui.container.MainScreen;

public class MyScreen extends MainScreen implements FieldChangeListener{

public static final long ID = 0x5d8a91784555e0f8L;

private PersistentObject dataStore;

private BasicEditField userNameField;
private BasicEditField companyField;
private BasicEditField titleField;
private BasicEditField ageField;
private ButtonField saveButton;

private MyData myData;

public MyScreen(){
  super();
  setTitle("Persist Data Test");
  initialize();
  addToWindow();
  recoverDataFromStore();
}

private void initialize(){
  userNameField = new BasicEditField("User Name: ", "", 20, BasicEditField.FILTER_DEFAULT);
  companyField = new BasicEditField("Company Name: ", "", 20, BasicEditField.FILTER_DEFAULT);
  titleField = new BasicEditField("Title: ", "", 20, BasicEditField.FILTER_DEFAULT);
  ageField = new BasicEditField("Age: ", "", 20, BasicEditField.FILTER_NUMERIC);
        saveButton = new ButtonField("save");
  saveButton.setChangeListener(this);
}

private void addToWindow(){
  add(userNameField);
  add(titleField);
  add(companyField);
  add(ageField);
  add(saveButton);
}

public void saveData(){

  if (myData == null){
   myData = new MyData();
  }

  myData.setUserName(userNameField.getText());
  myData.setCompany(companyField.getText());
  myData.setTitle(titleField.getText());
  myData.setAge(Integer.valueOf(ageField.getText()).intValue());

  if (dataStore == null){
   dataStore = PersistentStore.getPersistentObject(ID);
  }

  synchronized(dataStore){
   if (dataStore.getContents() == null){
    dataStore.setContents(myData);
    dataStore.commit();
   }
  }
}

public void recoverDataFromStore(){

  if (dataStore == null){
   dataStore = PersistentStore.getPersistentObject(ID);
  }

  synchronized(dataStore){

   if (dataStore.getContents() != null){
    myData = (MyData) dataStore.getContents();
   }
  }

  if (myData != null){
   userNameField.setText(myData.getUserName());
   companyField.setText(myData.getCompany());
   titleField.setText(myData.getTitle());
   ageField.setText(myData.getAge()+"");
  }
}

public void fieldChanged(Field field, int context) {
  if (field == saveButton){
   saveData();
  }
}

}