BlackBerry开发平台的永久存储-Persistent Store

本文和大家重点学习一下Blackberry开发平台的永久存储-PersistentStore，主要包括BlackberrySDK5.0版本支持三种存储方式，PersistentStore存储对数据类型和对象的要求等内容，相信通过本文的学习你对Blackberry开发平台的永久存储-PersistentStore的概念一定会有深入的了解。

Blackberry开发平台的永久存储-PersistentStore

BlackberrySDK5.0版本支持三种存储方式：

◆RMS-RecordStore
◆PersistentStore-persistentstoreforRIMlet
◆SQLLiteforRIMlet

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。SQLLite是数据库方式存储，支持SQL语句，这是5.0SDK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。

BlackBerry开发平台中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-Valuepair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classMyData:

publicclassMyDataimplementsPersistable{  
 
privateStringm_userName;  
privateStringm_company;  
privateStringm_title;  
privateintm_age;  
 
publicMyData(){}  
 
publicvoidsetUserName(StringuserName){  
m_userName=userName;  
}  
 
publicStringgetUserName(){  
returnm_userName;  
}  
 
publicvoidsetCompany(Stringcompany){  
m_company=company;  
}  
 
publicStringgetCompany(){  
returnm_company;  
}  
 
publicvoidsetTitle(Stringtitle){  
m_title=title;  
}  
publicStringgetTitle(){  
returnm_title;  
}  
publicvoidsetAge(intage){  
m_age=age;  
}  
publicintgetAge(){  
returnm_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instancevariable都是基本类型，也可以有方法。

2.存储数据

publicstaticfinallongID=0x5d8a91784555e0f8L;  
 
publicvoidsaveData(){  
 
if(myData==null){  
myData=newMyData();  
}  
 
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-valuepair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

publicstaticfinallongID=0x5d8a91784555e0f8L;  
 
publicvoidrecoverDataFromStore(){  
 
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BlackBerry开发平台中PersistentStore的完整例子代码，可以拷贝到Eclipse里运行：

importnet.rim.device.api.ui.UiApplication;  
publicclassMyAppextendsUiApplication{  
publicstaticvoidmain(String[]args){  
MyAppapp=newMyApp();  
app.enterEventDispatcher();  
}  
 
publicMyApp(){  
MyScreenmyScreen=newMyScreen();  
pushScreen(myScreen);  
}  
}  
 
importnet.rim.device.api.util.Persistable;  
publicclassMyDataimplementsPersistable{  
 
privateStringm_userName;  
privateStringm_company;  
privateStringm_title;  
privateintm_age;  
 
publicMyData(){}  
 
publicvoidsetUserName(StringuserName){  
m_userName=userName;  
}  
 
publicStringgetUserName(){  
returnm_userName;  
}  
 
publicvoidsetCompany(Stringcompany){  
m_company=company;  
}  
 
publicStringgetCompany(){  
returnm_company;  
}  
 
publicvoidsetTitle(Stringtitle){  
m_title=title;  
}  
 
publicStringgetTitle(){  
returnm_title;  
}  
 
publicvoidsetAge(intage){  
m_age=age;  
}  
 
publicintgetAge(){  
returnm_age;  
}  
}  
 
importnet.rim.device.api.system.PersistentObject;  
importnet.rim.device.api.system.PersistentStore;  
importnet.rim.device.api.ui.Field;  
importnet.rim.device.api.ui.FieldChangeListener;  
importnet.rim.device.api.ui.component.BasicEditField;  
importnet.rim.device.api.ui.component.ButtonField;  
importnet.rim.device.api.ui.component.LabelField;  
importnet.rim.device.api.ui.container.MainScreen;  
 
publicclassMyScreenextendsMainScreenimplementsFieldChangeListener{  
 
publicstaticfinallongID=0x5d8a91784555e0f8L;  
 
privatePersistentObjectdataStore;  
 
privateBasicEditFielduserNameField;  
privateBasicEditFieldcompanyField;  
privateBasicEditFieldtitleField;  
privateBasicEditFieldageField;  
privateButtonFieldsaveButton;  
 
privateMyDatamyData;  
 
publicMyScreen(){  
super();  
setTitle("PersistDataTest");  
initialize();  
addToWindow();  
recoverDataFromStore();  
}  
 
privatevoidinitialize(){  
userNameField=newBasicEditField("UserName:","",20,BasicEditField.FILTER_DEFAULT);  
companyField=newBasicEditField("CompanyName:","",20,BasicEditField.FILTER_DEFAULT);  
titleField=newBasicEditField("Title:","",20,BasicEditField.FILTER_DEFAULT);  
ageField=newBasicEditField("Age:","",20,BasicEditField.FILTER_NUMERIC);  
saveButton=newButtonField("save");  
saveButton.setChangeListener(this);  
}  
 
privatevoidaddToWindow(){  
add(userNameField);  
add(titleField);  
add(companyField);  
add(ageField);  
add(saveButton);  
}  
 
publicvoidsaveData(){  
 
if(myData==null){  
myData=newMyData();  
}  
 
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();  
}  
}  
}  
 
publicvoidrecoverDataFromStore(){  
 
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()+"");  
}  
}  
 
publicvoidfieldChanged(Fieldfield,intcontext){  
if(field==saveButton){  
saveData();  
}  
}  
}