Android开发—数据库应用—访问数据表（SQLite OpenHelper） —添加检索操作（Retrieve）

/* (程序头部注释开始)
* 程序的版权和版本声明部分
* Copyright (c) 2011, 烟台大学计算机学院学生
* All rights reserved.
* 文件名称：数据库应用—添加检索操作（Retrieve）

* 作 者： 雷恒鑫
* 完成日期： 2012 年 08 月 14 日
* 版 本 号： V1.0
* 对任务及求解方法的描述部分
* 输入描述：
* 问题描述：
* 程序输出：

* 程序头部的注释结束

*/

 

 

以前用过的“db.rawQuery”语句可以用来直接做SQL查询（程序如下），

public Cursor getall() {         return db.rawQuery("SELECT * FROM notes", null);        }  

并返回查询结果的指针，如果想实现检索功能，可以再程序中使用更具弹性的“query”方法，来替换直接执行“SQL”语句的“rawQuery”方法。

 

修改后的“DummyDbAdapter.java”文件如下：

package com.demo.android.dummynote;import android.content.Context;import android.database.Cursor;import android.database.SQLException;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;import android.database.sqlite.SQLiteDatabase.CursorFactory;public class NotesDbAdapter {private static final String DATABASE_NAME = "notes.db";private static final int DATABASE_VERSION = 1;private static final String DATABASE_TABLE = "notes";private static final String DATABASE_CREATE = "creat table notes("+ "_id INTEGER PRIMARY KEY," + "note TEXT," + "created INTEGER,"+ "modified INTEGER" + ");";private static class DatabaseHelper extends SQLiteOpenHelper {public DatabaseHelper(Context context) {super(context, DATABASE_NAME, null, DATABASE_VERSION);// TODO Auto-generated constructor stub}@Overridepublic void onCreate(SQLiteDatabase db) {// TODO Auto-generated method stubdb.execSQL(DATABASE_CREATE);}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {// TODO Auto-generated method stubdb.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);onCreate(db);}}private Context mCtx = null;private DatabaseHelper dbHelper;private SQLiteDatabase db;public NotesDbAdapter(Context ctx) {this.mCtx = ctx;}public NotesDbAdapter open() throws SQLException {dbHelper = new DatabaseHelper(mCtx);db = dbHelper.getWritableDatabase();return this;}public void close() {dbHelper.close();}private static final String KEY_ROWID = "_id";static final String KEY_NOTE = "note";private static final String KEY_CREATED = "created";String[] strCols = new String[]{KEY_ROWID,KEY_NOTE,KEY_CREATED,};// get all entriespublic Cursor getall() {return db.query(DATABASE_TABLE, //Which table to SelectstrCols, //Which columns to returnnull, //WHERE clausenull, //WHERE argumentsnull, //GROUP BY clausenull, //HAVING clausenull);//Order-by clause}}

重构：

由于“”字件符串只会在“”语句中使用一次，因此为了省下内存空间，而少声明一个“”变量，即将“”与“”两段和写在一起，在其他程序中碰到次状况，也可以这样处理。

修改后的“DummyDbAdapter.java”文件如下：

package com.demo.android.dummynote;import android.content.Context;import android.database.Cursor;import android.database.SQLException;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;import android.database.sqlite.SQLiteDatabase.CursorFactory;public class NotesDbAdapter {private static final String DATABASE_NAME = "notes.db";private static final int DATABASE_VERSION = 1;private static final String DATABASE_TABLE = "notes";private static final String DATABASE_CREATE = "creat table notes("+ "_id INTEGER PRIMARY KEY," + "note TEXT," + "created INTEGER,"+ "modified INTEGER" + ");";private static class DatabaseHelper extends SQLiteOpenHelper {public DatabaseHelper(Context context) {super(context, DATABASE_NAME, null, DATABASE_VERSION);// TODO Auto-generated constructor stub}@Overridepublic void onCreate(SQLiteDatabase db) {// TODO Auto-generated method stubdb.execSQL(DATABASE_CREATE);}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {// TODO Auto-generated method stubdb.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE);onCreate(db);}}private Context mCtx = null;private DatabaseHelper dbHelper;private SQLiteDatabase db;public NotesDbAdapter(Context ctx) {this.mCtx = ctx;}public NotesDbAdapter open() throws SQLException {dbHelper = new DatabaseHelper(mCtx);db = dbHelper.getWritableDatabase();return this;}public void close() {dbHelper.close();}private static final String KEY_ROWID = "_id";static final String KEY_NOTE = "note";private static final String KEY_CREATED = "created";// get all entriespublic Cursor getall() {return db.query(DATABASE_TABLE, //Which table to Selectnew String[]{KEY_ROWID,KEY_NOTE,KEY_CREATED}, //Which columns to returnnull, //WHERE clausenull, //WHERE argumentsnull, //GROUP BY clausenull, //HAVING clausenull);//Order-by clause}}