SQLite数据库的简单应用；

 1 package com.scott.db;
 2 
 3 import android.content.Context;
 4 import android.database.sqlite.SQLiteDatabase;
 5 import android.database.sqlite.SQLiteOpenHelper;
 6 
 7 public class DBHelper extends SQLiteOpenHelper {
 8 
 9     private static final String DATABASE_NAME = "test.db";
10     private static final int DATABASE_VERSION = 1;
11     
12     public DBHelper(Context context) {
13         //CursorFactory设置为null,使用默认值
14         super(context, DATABASE_NAME, null, DATABASE_VERSION);
15     }
16 
17     //数据库第一次被创建时onCreate会被调用
18     @Override
19     public void onCreate(SQLiteDatabase db) {
20         db.execSQL("CREATE TABLE IF NOT EXISTS person" +
21                 "(_id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, age INTEGER, info TEXT)");
22     }
23 
24     //如果DATABASE_VERSION值被改为2,系统发现现有数据库版本不同,即会调用onUpgrade
25     @Override
26     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
27         db.execSQL("ALTER TABLE person ADD COLUMN other STRING");
28     }
29 }

package com.scott.db;

import java.util.ArrayList;
import java.util.List;

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

public class DBManager {
    private DBHelper helper;
    private SQLiteDatabase db;
    
    public DBManager(Context context) {
        helper = new DBHelper(context);
        //因为getWritableDatabase内部调用了mContext.openOrCreateDatabase(mName, 0, mFactory);
        //所以要确保context已初始化,我们可以把实例化DBManager的步骤放在Activity的onCreate里
        db = helper.getWritableDatabase();
    }
    
    /**
     * add persons
     * @param persons
     */
    public void add(List<Person> persons) {
        db.beginTransaction();    //开始事务
        try {
            for (Person person : persons) {
                db.execSQL("INSERT INTO person VALUES(null, ?, ?, ?)", new Object[]{person.name, person.age, person.info});
            }
            db.setTransactionSuccessful();    //设置事务成功完成
        } finally {
            db.endTransaction();    //结束事务
        }
    }
    
    /**
     * update person‘s age
     * @param person
     */
    public void updateAge(Person person) {
        ContentValues cv = new ContentValues();
        cv.put("age", person.age);
        db.update("person", cv, "name = ?", new String[]{person.name});
    }
    
    /**
     * delete old person
     * @param person
     */
    public void deleteOldPerson(Person person) {
        db.delete("person", "age >= ?", new String[]{String.valueOf(person.age)});
    }
    
    /**
     * query all persons, return list
     * @return List<Person>
     */
    public List<Person> query() {
        ArrayList<Person> persons = new ArrayList<Person>();
        Cursor c = queryTheCursor();
        while (c.moveToNext()) {
            Person person = new Person();
            person._id = c.getInt(c.getColumnIndex("_id"));
            person.name = c.getString(c.getColumnIndex("name"));
            person.age = c.getInt(c.getColumnIndex("age"));
            person.info = c.getString(c.getColumnIndex("info"));
            persons.add(person);
        }
        c.close();
        return persons;
    }
    
    /**
     * query all persons, return cursor
     * @return    Cursor
     */
    public Cursor queryTheCursor() {
        Cursor c = db.rawQuery("SELECT * FROM person", null);
        return c;
    }
    
    /**
     * close database
     */
    public void closeDB() {
        db.close();
    }
}