Android开发—数据库应用—访问数据表（SQLite OpenHelper）

/* (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—访问数据表（SQLite OpenHelper）

* 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

*/

在“DummyNote”项目的“src/com/demo/android/dummynote”目录下新建一个“NotesDbAdapter.java”文件，程序的主框架如下：

package com.demo.android.dummynote;

import android.content.Context;
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
		}
		@Override
		public void onCreate(SQLiteDatabase db) {
			// TODO Auto-generated method stub
			db.execSQL(DATABASE_CREATE);
			
		}
		@Override
		public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
			// TODO Auto-generated method stub
			db.execSQL("DROP TABLE IF EXISTS "+DATABASE_TABLE);
			onCreate(db);
		}
}
}

对“NotesDbAdapter”类进行加工：

在“NotesDbAdapter.java”文件里继续添加代码：

package com.demo.android.dummynote;

import android.content.Context;
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
		}
		@Override
		public void onCreate(SQLiteDatabase db) {
			// TODO Auto-generated method stub
			db.execSQL(DATABASE_CREATE);
			
		}
		@Override
		public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
			// TODO Auto-generated method stub
			db.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();
}
}

在打开“DummyNote.java”文件，修改“setAdapter”函数如下：

private NotesDbAdapter mDbHelper;
    private void setAdapter(){
    	mDbHelper = new NotesDbAdapter(this);
    	mDbHelper.open();
    	ListAdapter adapter = new ArrayAdapter<String>(this,
    			android.R.layout.simple_list_item_1,note_array);
    	setListAdapter(adapter);
    }

完整的“DummyNote.java”文件如下：

package com.demo.android.dummynote;

import android.app.ListActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;

public class DummyNote extends ListActivity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //Tell the list view which view to display when the list is empty
        getListView().setEmptyView(findViewById(R.id.empty));
        setAdapter();
    }
    private String[] note_array = {
    		"gasolin",
    		"crota",
    		"louk",
    		"magicion"
    }; 
    private NotesDbAdapter mDbHelper;
    private void setAdapter(){
    	mDbHelper = new NotesDbAdapter(this);
    	mDbHelper.open();
    	ListAdapter adapter = new ArrayAdapter<String>(this,
    			android.R.layout.simple_list_item_1,note_array);
    	setListAdapter(adapter);
    }
}

验证： 使用“adb shell”命令，进入“cddata/data/com.deno.android.dummynote/databases”目录后，执行“sqlite3 notes.db”命令，查看“notes”数据表是否已经创建。

从上面的结果看，“notes”数据表以经正确创建了，我们可以通过“sqlite>”互动模式来尝试在“notes”数据表中增加几条数据：

查看新增内容是否正确（用SELECT”语句）：

可以看到，数据分成3列，分别为“_id”、“note”、“created”。每个字段中确实都有填入数值。