Android开发—数据库应用—访问数据表（SQLite OpenHelper） —查询单条记录、修改
/* (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—查询单条记录、修改
* 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“NotesDbAdapter”类中“查询单条记录”与“修改”的程序代码写好，程序如下：
//query single entry public Cursor get(long rowId) throws SQLException { Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NOTE, KEY_CREATED}, KEY_ROWID + "=" + rowId, null, null, null, null, null); if (mCursor != null) { mCursor.moveToFirst(); } return mCursor; } //update public boolean update(long rowId, String note) { ContentValues args = new ContentValues(); args.put(KEY_NOTE, note); return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0; }
完整的“NotesDbAdapter.java”程序如下：
package com.demo.android.dummynote;import java.sql.Date;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;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} // add an entry public long create(String Note) { Date now = new Date(); ContentValues args = new ContentValues(); args.put(KEY_NOTE, Note); args.put(KEY_CREATED, now.getTime()); return db.insert(DATABASE_TABLE, null, args); }//remove an entrypublic boolean delete(long rowID){return db.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowID,null)>0;} //query single entry public Cursor get(long rowId) throws SQLException { Cursor mCursor = db.query(true, DATABASE_TABLE, new String[] {KEY_ROWID, KEY_NOTE, KEY_CREATED}, KEY_ROWID + "=" + rowId, null, null, null, null, null); if (mCursor != null) { mCursor.moveToFirst(); } return mCursor; } //update public boolean update(long rowId, String note) { ContentValues args = new ContentValues(); args.put(KEY_NOTE, note); return db.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0; }}
注意，以上程序 Date now = new Date();有一点小小的错误，编译器提示如下：
构造函数 Date（）未定义；
但是书上Date now = new Date()括号里面却没有参数，大家如果知道是怎么回事，在评论上告诉我一声哈。
顺便把“DummyNote”程序写一下：
package com.demo.android.dummynote;import android.app.ListActivity;import android.database.Cursor;import android.os.Bundle;import android.view.Menu;import android.view.MenuItem;import android.widget.ArrayAdapter;import android.widget.ListAdapter;import android.widget.SimpleCursorAdapter;import android.content.Intent;import android.widget.ListView;///////////////////////////////////////////////////////import android.app.ListActivity;import android.content.Intent;import android.database.Cursor;import android.os.Bundle;import android.util.Log;import android.view.ContextMenu;import android.view.Menu;import android.view.MenuItem;import android.view.View;import android.view.ContextMenu.ContextMenuInfo;import android.widget.AdapterView;import android.widget.ListView;import android.widget.SimpleCursorAdapter;/////////////////////////////////////////////////////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 Cursor mNotesCursor; private void setAdapter(){ mDbHelper = new NotesDbAdapter(this); mDbHelper.open(); fillData(); } private void fillData(){ mNotesCursor = mDbHelper.getall(); startManagingCursor(mNotesCursor); //Create an array to specify the field we want to display in the list String[] from = new String[]{NotesDbAdapter.KEY_NOTE}; //an array of the fields we want to bind those fields to int[] to = new int[]{android.R.id.text1}; //Now create a simple cursor adapter SimpleCursorAdapter adapter = new SimpleCursorAdapter(this, android.R.layout.simple_list_item_1,mNotesCursor,from,to); setListAdapter(adapter); } private int mNoteNumber = 1; protected static final int MENU_INSERT = Menu.FIRST; protected static final int MENU_DELETE = Menu.FIRST+1; protected static final int MENU_MODIFY = Menu.FIRST+1; @Overridepublic boolean onCreateOptionsMenu(Menu menu) {// TODO Auto-generated method stubsuper.onCreateOptionsMenu(menu);menu.add(0, MENU_INSERT, 0, "新增记事");menu.add(0, MENU_DELETE, 0, "删除记事");return super.onCreateOptionsMenu(menu);}@Overridepublic boolean onOptionsItemSelected(MenuItem item) {// TODO Auto-generated method stubswitch(item.getItemId()) { case MENU_INSERT: String noteName = "Note " + mNoteNumber++; mDbHelper.create(noteName); fillData(); return true; case MENU_DELETE: mDbHelper.delete(getListView().getSelectedItemId()); fillData(); return true;}return super.onOptionsItemSelected(item);}}
大家如果知道问题的解决思路别忘了告诉我一声哈。