本篇博文主要实现简单的创建数据库以及实现CRUD操作。
首先，我们建立一个Android Project，命名为db
用SQLiteOpenHelper类中的getWritableDatabase()和getReadableDatabase()都可以获取一个操作数据库的SQLiteDatabase实例，其中getReadableDatabase()方法中会调用getWritableDatabase()方法。
区别：其中，getWritableDatabase() 方法以读写方式打开数据库，一旦数据库的磁盘空间满了，数据库就只能读而不能写，倘若使用的是getWritableDatabase() 方法就会出错。getReadableDatabase()方法则是先以读写方式打开数据库，如果数据库的磁盘空间满了，就会打开失败，当打开失败后会继续尝试以只读方式打开数据库；如果此时数据库空间出现了空余，则会成功获取一个操作数据库的SQLiteDatabase对象。
我们首先建立一个类（继承SQLiteOpenHelper）DBOpenHelper.java：
package cn.itcast.service;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
public class DBOpenHelper extends SQLiteOpenHelper {
//构造函数，调用父类的SQLiteOpenHelper的构造函数
public DBOpenHelper(Context context) {
super(context, "itcast.db", null, 1);
//<包>/databases/
}
@Override
public void onCreate(SQLiteDatabase db) {//是在数据库每一次被创建的时候调用的
db.execSQL("CREATE TABLE person(personid integer primary key autoincrement, name varchar(20), phone VARCHAR(12) NULL)");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {//在数据库的版本发生变化时会被调用
db.execSQL("ALTER TABLE person ADD amount integer");
}
}
onCreate()方法在初次生成数据库时才会被调用，在onCreate()方法里可以生成数据库表结构及添加一些应用使用到的初始化数据。
onUpgrade()方法在数据库的版本发生变化时会被调用，一般在软件升级时才需改变版本号，而数据库的版本是由程序员控制的。
然后，我们建立一个测试类，来实现调用DBOpenHelper中的方法来创建数据库DBTest.java：
package cn.itcast.test;
public class DBTest extends AndroidTestCase {
public void testCreateDB() throws Exception{
DBOpenHelper dbOpenHelper = new DBOpenHelper(getContext());
dbOpenHelper.getWritableDatabase();
}
}关于测试需要在AndroidManifest.xml中配置几条语句，这点不要忘了。
运行测试发现在File Explorer视图中的/data/data/cn.itcast.db/databases目录下有个itcast.db的文件，就是我们创建的数据库了。
我们用Person来做例子
首先，用建立一个javabean：Person.java
package cn.itcast.domain;
public class Person {
private Integer id;
private String name;
private String phone;
private Integer amount;
public Person(){}
public Person(String name, String phone, Integer amount) {
this.name = name;
this.phone = phone;
this.amount = amount;
}
public Person(Integer id, String name, String phone, Integer amount) {
this.id = id;
this.name = name;
this.phone = phone;
this.amount = amount;
}
public Integer getAmount() {
return amount;
}
public void setAmount(Integer amount) {
this.amount = amount;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPhone() {
return phone;
}
public void setPhone(String phone) {
this.phone = phone;
}
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + ", phone=" + phone
+ ", amount=" + amount + "]";
}
}
然后，我们需要编写业务层的类，PersonService.java
package cn.itcast.service;
import java.util.ArrayList;
import java.util.List;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import cn.itcast.domain.Person;
public class PersonService {
private DBOpenHelper dbOpenHelper;
public PersonService(Context context) {
this.dbOpenHelper = new DBOpenHelper(context);
}
/**
* 添加记录
* @param person
*/
public void save(Person person){
SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
db.execSQL("insert into person(name, phone, amount) values(?,?,?)",
new Object[]{person.getName(), person.getPhone(), person.getAmount()});
}
/**
* 删除记录
* @param id 记录ID
*/
public void delete(Integer id){
SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
db.execSQL("delete from person where personid=?", new Object[]{id});
}
/**
* 更新记录
* @param person
*/
public void update(Person person){
SQLiteDatabase db = dbOpenHelper.getWritableDatabase();
db.execSQL("update person set name=?,phone=?,amount=? where personid=?",
new Object[]{person.getName(), person.getPhone(), person.getAmount(), person.getId()});
}
/**
* 查询记录
* @param id 记录ID
* @return
*/
public Person find(Integer id){
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
Cursor cursor = db.rawQuery("select * from person where personid=?", new String[]{id.toString()});
if(cursor.moveToFirst()){
int personid = cursor.getInt(cursor.getColumnIndex("personid"));
int amount = cursor.getInt(cursor.getColumnIndex("amount"));
String name = cursor.getString(cursor.getColumnIndex("name"));
String phone = cursor.getString(cursor.getColumnIndex("phone"));
return new Person(personid, name, phone, amount);
}
cursor.close();
return null;
}
/**
* 分页获取记录
* @param offset 跳过前面多少条记录
* @param maxResult 每页获取多少条记录
* @return
*/
public List<Person> getScrollData(int offset, int maxResult){
List<Person> persons = new ArrayList<Person>();
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
Cursor cursor = db.rawQuery("select * from person order by personid asc limit ?,?",
new String[]{String.valueOf(offset), String.valueOf(maxResult)});
while(cursor.moveToNext()){
int personid = cursor.getInt(cursor.getColumnIndex("personid"));
int amount = cursor.getInt(cursor.getColumnIndex("amount"));
String name = cursor.getString(cursor.getColumnIndex("name"));
String phone = cursor.getString(cursor.getColumnIndex("phone"));
persons.add(new Person(personid, name, phone, amount));
}
cursor.close();
return persons;
}
/**
* 分页获取记录
* @param offset 跳过前面多少条记录
* @param maxResult 每页获取多少条记录
* @return
*/
public Cursor getCursorScrollData(int offset, int maxResult){
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
Cursor cursor = db.rawQuery("select personid as _id,name,phone,amount from person order by personid asc limit ?,?",
new String[]{String.valueOf(offset), String.valueOf(maxResult)});
return cursor;
}
/**
* 获取记录总数
* @return
*/
public long getCount(){
SQLiteDatabase db = dbOpenHelper.getReadableDatabase();
Cursor cursor = db.rawQuery("select count(*) from person", null);
cursor.moveToFirst();
long result = cursor.getLong(0);
cursor.close();
return result;
}
}
然后，我们就需要执行测试了PersonServiceTest.java:
package cn.itcast.test;
import java.util.List;
import cn.itcast.domain.Person;
import cn.itcast.service.DBOpenHelper;
import cn.itcast.service.PersonService;
import android.test.AndroidTestCase;
import android.util.Log;
public class PersonServiceTest extends AndroidTestCase {
private static final String TAG = "PersonServiceTest";
public void testCreateDB() throws Exception{
DBOpenHelper dbOpenHelper = new DBOpenHelper(getContext());
dbOpenHelper.getWritableDatabase();
}
public void testSave() throws Exception{
PersonService service = new PersonService(this.getContext());
for(int i = 0 ; i < 20 ; i++){
Person person = new Person("zhangxx"+ i, "136765765"+ i, 100);
service.save(person);
}
}
public void testDelete() throws Exception{
PersonService service = new PersonService(this.getContext());
service.delete(21);
}
public void testUpdate() throws Exception{
PersonService service = new PersonService(this.getContext());
Person person = service.find(1);
person.setName("zhangxiaoxiao");
service.update(person);
}
public void testFind() throws Exception{
PersonService service = new PersonService(this.getContext());
Person person = service.find(1);
Log.i(TAG, person.toString());
}
public void testScrollData() throws Exception{
PersonService service = new PersonService(this.getContext());
List<Person> persons = service.getScrollData(0, 5);
for(Person person : persons){
Log.i(TAG, person.toString());
}
}
public void testCount() throws Exception{
PersonService service = new PersonService(this.getContext());
long result = service.getCount();
Log.i(TAG, result+"");
}
public void testUpdateAmount() throws Exception{
PersonService service = new PersonService(this.getContext());
Person person1 = service.find(1);
Person person2 = service.find(2);
person1.setAmount(100);
person2.setAmount(50);
service.update(person1);
service.update(person2);
}
}
可以在找到itcast.db之后，通过下载：SQLite Explorer来打开查看
Android开发系列（九）：创建数据库以及完成简单的CRUD操作
原文地址：http://blog.csdn.net/u010800530/article/details/39270925
