SQLite使用方法

Android系统集成了一个轻量级的数据库SQLite，是一个嵌入式的数据库引擎，适用于资源有限的设备适量数据存取

Android提供了SQLiteOpenHelper类，作为访问SQLite的助手类，通常都会继承SQLiteOpenHelper开发子类

SQLiteOpenHelper类提供两个方面的功能：

第一，getReadableDatabase(),getWritableDatabase()可以获得SQLiteDatabse对象，通过该对象可以对数据库进行操作

第二，提供了onCreate()和onUpgrade()两个回调函数，允许我们在创建和升级数据库时，进行自己的操作

例程：

DatabaseHelper.java

import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteDatabase.CursorFactory;import android.database.sqlite.SQLiteOpenHelper;public class DatabaseHelper extends SQLiteOpenHelper {private static final int VERSION  = 1;//在SQLiteOepnHelper的子类当中，必须有该构造函数public DatabaseHelper(Context context, String name, CursorFactory factory,int version) {//必须通过super调用父类当中的构造函数super(context, name, factory, version);// TODO Auto-generated constructor stub}public DatabaseHelper(Context context, String name) {this(context, name, VERSION);// TODO Auto-generated constructor stub}public DatabaseHelper(Context context,String name,int version){this(context,name,null,version);}@Overridepublic void onCreate(SQLiteDatabase db) {// TODO Auto-generated method stubSystem.out.println("create a Database");//execSQL函数用于执行SQL语句，创建一个表名为user,有两列数据id、namedb.execSQL("create table user(id int,name varchar(20))");}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {// TODO Auto-generated method stubSystem.out.println("update a Database");}}

主要Activity

SQLiteActivity.java(五个按钮：创建数据库、更新数据库版本、插入数据、更新数据、查询数据、删除数据)

import android.app.Activity;import android.content.ContentValues;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.os.Bundle;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import com.mars.sqlite.db.DatabaseHelper;public class SQLiteActivity extends Activity {private Button createButton;private Button updateButton;private Button insertButton;private Button updateRecordButton;private Button queryButton;private Button deleteButton; @Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);createButton = (Button)findViewById(R.id.createDatabase);updateButton = (Button)findViewById(R.id.updateDatabase);insertButton = (Button)findViewById(R.id.insert);updateRecordButton = (Button)findViewById(R.id.update);queryButton = (Button)findViewById(R.id.query);deleteButton = (Button)findViewById(R.id.delete);createButton.setOnClickListener(new CreateListener());updateButton.setOnClickListener(new UpdateListener());insertButton.setOnClickListener(new InsertListener());updateRecordButton.setOnClickListener(new UpdateRecordListener());queryButton.setOnClickListener(new QueryListener());deleteButton.setOnClickListener(new DeleteListener());}class CreateListener implements OnClickListener{public void onClick(View v){DatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this, "test_db");//只有调用了DatabaseHelper对象的getReadableDatabase()方法，或者是getWritableDatabase()方法之后，才会创建，或打开一个数据库SQLiteDatabase db = dbHelper.getReadableDatabase();}}class UpdateListener implements OnClickListener{@Overridepublic void onClick(View v) {DatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this, "test_db",2);SQLiteDatabase db = dbHelper.getReadableDatabase();}}//insert into <表名>（key1,key2,..） values（value1，value2） whereclass InsertListener implements OnClickListener{@Overridepublic void onClick(View v) {ContentValues values = new ContentValues();values.put("id",1);values.put("name","wanger");DatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this, "test_db",2);SQLiteDatabase db = dbHelper.getWritableDatabase();db.insert("user", null, values);}}    //updata table_name set XXCOL=XXX where XXCOL=XX...class UpdateRecordListener implements OnClickListener{@Overridepublic void onClick(View v) {DatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this, "test_db",2);SQLiteDatabase db = dbHelper.getWritableDatabase();ContentValues values = new ContentValues();values.put("name", "wangerniang");db.update("user",values,"id = ?",new String[]{"1"});}}class QueryListener implements OnClickListener{@Overridepublic void onClick(View v) {DatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this,"test_db",2);SQLiteDatabase db = dbHelper.getReadableDatabase();Cursor cursor = db.query("user", new String[]{"id","name"}, "id=?", new String[]{"1"}, null, null, null);while(cursor.moveToNext()){String name = cursor.getString(cursor.getColumnIndex("name"));System.out.println("query--->" + name);}}}//delete <table> where <whereClause>class DeleteListener implements OnClickListener{@Overridepublic void onClick(View v) {// TODO Auto-generated method stubDatabaseHelper dbHelper = new DatabaseHelper(SQLiteActivity.this,"test_db",2);SQLiteDatabase db = dbHelper.getWritableDatabase();db.delete("user", "name = ?",new String[]{"wanger"} );}}}

备注:

当更新数据库的版本为2时，后面增改查删操作之前打开数据库就要用版本为2，

如果选择默认（默认版本为1），会报错（不能从版本2降级到版本1）