Android development-Database Application-SQLite OpenHelper-Retrieve)

/* (Start of program header annotation)
* Copyright and version Declaration of the program
* Copyright (c) 2011, a student from the computer College of Yantai University
* All rights reserved.
* File name: Database Application-Retrieve)
* Author: Lei hengxin
* Completion date: January 1, August 14, 2012
* Version No.: V1.0
* Description of tasks and Solutions
* Input description:
* Problem description:
* Program output:
* End the comment in the program Header
*/
 
 
The previously used "db. rawQuery" statement can be used for SQL queries directly (the program is as follows ),
[Java]
Public Cursor getall (){
Return db. rawQuery ("SELECT * FROM notes", null );

}
Return the query result pointer. If you want to implement the search function, you can use the more flexible "query" method in the program to replace the "rawQuery" method that runs the "SQL" statement directly.
 
The modified "DummyDbAdapter. java" file is as follows:
[Java]
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
}
 
@ Override
Public void onCreate (SQLiteDatabase db ){
// TODO Auto-generated method stub
Db.exe cSQL (DATABASE_CREATE );
 
}
 
@ Override
Public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion ){
// TODO Auto-generated method stub
Db.exe cSQL ("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 entries
Public Cursor getall (){
Return db. query (DATABASE_TABLE, // Which table to Select
StrCols, // Which columns to return
Null, // WHERE clause
Null, // WHERE arguments
Null, // group by clause
Null, // HAVING clause
Null); // Order-by clause
 
}
}

Refactoring:
Because the "" symbol string is used only once in the "" statement, a "" variable is rarely declared to save memory space, the two sections "" and "" will be written together. You can also handle the situation in other programs.
The modified "DummyDbAdapter. java" file is as follows:
[Java]
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
}
 
@ Override
Public void onCreate (SQLiteDatabase db ){
// TODO Auto-generated method stub
Db.exe cSQL (DATABASE_CREATE );
 
}
 
@ Override
Public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion ){
// TODO Auto-generated method stub
Db.exe cSQL ("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 entries
Public Cursor getall (){
Return db. query (DATABASE_TABLE, // Which table to Select
New String [] {KEY_ROWID, KEY_NOTE, KEY_CREATED}, // Which columns to return
Null, // WHERE clause
Null, // WHERE arguments
Null, // group by clause
Null, // HAVING clause
Null); // Order-by clause
 
}
}

Author: leihengxin