android数据持久化之SQLite

简单讲解SQLite关系数据库存储数据的用法
创建DBAdapter辅助类，封装访问数据库的操作
[java]
package com.example.mydatabase;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DBAdapter {
static final String KEY_ROWID = "_id";
static final String KEY_NAME = "name";
static final String KEY_EMAIL = "email";
static final String TAG = "DBAdapter";

static final String DATABASE_NAME = "MyDB";
static final String DATABASE_TABLE = "contacts";
static final int DATABASE_VERSION = 2;

static final String DATABASE_CREATE = "create table contacts (_id integer primary key autoincrement,"
+ "name text not null, email text not null)";
final Context context;
DatabaseHelper DBHelper;
SQLiteDatabase db;

public DBAdapter(Context ctx){
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}

private static class DatabaseHelper extends SQLiteOpenHelper{

public DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
// TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
try{
db.execSQL(DATABASE_CREATE);
}catch (SQLException e){
e.printStackTrace();
}

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
db.execSQL("DROP TABLE IF EXISTS contacts");
onCreate(db);

}

}

public DBAdapter open() throws SQLException{
db = DBHelper.getWritableDatabase();
return this;
}

public void close(){
DBHelper.close();
}

public long insertContact(String name, String email){
ContentValues initiaValues = new ContentValues();
initiaValues.put(KEY_NAME, name);
initiaValues.put(KEY_EMAIL, email);
return db.insert(DATABASE_TABLE, null, initiaValues);
}

public boolean deleteContact(long rowId){
return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0;
}

public Cursor getAllContacts(){
return db.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NAME, KEY_EMAIL}, null, null, null, null, null);
}

public Cursor getContact(long rowId) throws SQLException{
Cursor mCursor = db.query(true, DATABASE_TABLE, new String[]{KEY_ROWID,KEY_NAME,KEY_EMAIL}, KEY_ROWID + "=" + rowId, null, null, null, null, null);
if(mCursor != null){
mCursor.moveToFirst();
}
return mCursor;
}

public boolean updateContact(long rowId, String name, String email){
ContentValues args = new ContentValues();
args.put(KEY_NAME, name);
args.put(KEY_EMAIL, email);
return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0;
}
}

[/java]
主程序文件
[java]
package com.example.mydatabase;

import android.os.Bundle;
import android.app.Activity;
import android.database.Cursor;
import android.view.Menu;
import android.widget.Toast;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DBAdapter db = new DBAdapter(this);

// db.open();
// long id = db.insertContact("gaoxueping", "gaoxueping@china.com");
// id = db.insertContact("andy", "andy@china.com");
// db.close();

db.open();
Cursor c = db.getAllContacts();
if(c.moveToFirst()){
do{
DisplayContact(c);
} while (c.moveToNext());
}
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}

public void DisplayContact(Cursor c){
Toast.makeText(this,
"id: " + c.getString(0) + "\n"
+"name: " + c.getString(1) + "\n"
+"email: " +c.getString(2),
Toast.LENGTH_LONG).show();
}

}

[/java]