本文和大家重點(diǎn)學(xué)習(xí)一下Blackberry開發(fā)平臺的永久存儲-PersistentStore，主要包括BlackberrySDK5.0版本支持三種存儲方式，PersistentStore存儲對數(shù)據(jù)類型和對象的要求等內(nèi)容，相信通過本文的學(xué)習(xí)你對Blackberry開發(fā)平臺的永久存儲-PersistentStore的概念一定會有深入的了解。

Blackberry開發(fā)平臺的永久存儲-PersistentStore

BlackberrySDK5.0版本支持三種存儲方式：

◆RMS-RecordStore
◆PersistentStore-persistentstoreforRIMlet
◆SQLLiteforRIMlet

RMS方式的存儲是基于byte數(shù)組的存儲，對象需要先序列化，再存儲。SQLLite是數(shù)據(jù)庫方式存儲，支持SQL語句，這是5.0SDK的新特性。Blackberry最成熟，最流行的存儲方式是PersistentStore，可以直接存儲對象。本文詳細(xì)介紹PersistentStore的方式。

BlackBerry開發(fā)平臺中PersistentStore存儲對數(shù)據(jù)類型和對象的要求：

◆被存儲對象只包含基本數(shù)據(jù)類型-int,String,long,boolean,byte,等等
◆被存儲類必須要執(zhí)行Persistable接口
◆PersistentStore以Key-Valuepair的方式進(jìn)行數(shù)據(jù)存儲，key必須是一個long值，value的類型是Object.下面來看一個例子：

1.創(chuàng)建存儲數(shù)據(jù)類，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類執(zhí)行了Persistable接口，這個接口沒有任何要執(zhí)行的函數(shù)。MyData的instancevariable都是基本類型，也可以有方法。

2.存儲數(shù)據(jù)

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的存儲，需要一個ID，對應(yīng)一個PersistentObject，存取數(shù)據(jù)時都要用到，一個ID只對應(yīng)一個PersistentObject。存儲第一步需要從PersistentStore中用ID獲取PersistentObject，再調(diào)用PersistentObject.setContents(Object)接口填入存儲對象，這步其實(shí)還沒有保存數(shù)據(jù)，需要調(diào)用PersistentObject.commit()保存數(shù)據(jù)。

3.獲取數(shù)據(jù)

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()+"");  
}  
}  
 

獲取數(shù)據(jù)第一步用ID獲取對應(yīng)的持久對象PersistentObject，在調(diào)用PersistentObject.getContents()獲取數(shù)據(jù)對象，獲取的對象類為Object，需要轉(zhuǎn)換成實(shí)際的類型，比如myData=(MyData)dataStore.getContents()。

如下是BlackBerry開發(fā)平臺中PersistentStore的完整例子代碼，可以拷貝到Eclipse里運(yùn)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();  
}  
}  
}