Slide 14.18: MySQLiteHelper.java (cont.)

MySQLiteHelper.java (Cont.)

It is the interface to global information about an application environment. It allows access to application-specific resources and classes, as well as up-calls for application-level operations such as launching activities, broadcasting and receiving intents, etc.

import android.database.sqlite.SQLiteDatabase;

It exposes methods to manage an SQLite database. SQLiteDatabase has methods to create, delete, execute SQL commands, and perform other common database management tasks.

import android.database.sqlite.SQLiteOpenHelper;

It manages database creation and version management. Developers create a subclass implementing

onCreate(SQLiteDatabase),
onUpgrade(SQLiteDatabase, int, int), and optionally
onOpen(SQLiteDatabase),

and this class takes care of opening the database if it exists, creating it if it does not, and upgrading it as necessary.

import android.util.Log;

It is an API for sending log output. Generally, use the following methods:

Log.e( ), which sends an ERROR log message and log the exception
Log.w( ), which sends a WARN log message and log the exception
Log.d( ), which sends a DEBUG log message and log the exception
Log.i( ), which sends an INFO log message and log the exception
Log.v( ), which sends a VERBOSE log message and log the exception

public class MySQLiteHelper extends SQLiteOpenHelper {

A subclass of SQLiteOpenHelper, such as MySQLiteHelper in this application, is often used to create and upgrade a database.

src/main/java/com/example/wenchen/sqlitedemo/MySQLiteHelper.java

package com.example.wenchen.sqlitedemo;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class MySQLiteHelper extends SQLiteOpenHelper {

  public static final String TABLE_COMMENTS = "comments";
  public static final String COLUMN_ID = "_id";
  public static final String COLUMN_COMMENT = "comment";

  private static final String DATABASE_NAME = "applicationdata";
  private static final int DATABASE_VERSION = 1;

  // create table comments (
  //   _id integer primary key autoincrement,
  //   comment text not null );   
  private static final String TABLE_CREATE = "create table "
    + TABLE_COMMENTS + "( " + COLUMN_ID + " integer primary key autoincrement, "
    + COLUMN_COMMENT + " text not null );";

  public MySQLiteHelper( Context context ) {
    super( context, DATABASE_NAME, null, DATABASE_VERSION );
  }

  @Override
  public void onCreate( SQLiteDatabase database ) {
    database.execSQL(  TABLE_CREATE );
  }

  @Override
  public void onUpgrade( SQLiteDatabase db, int oldVersion, int newVersion ) {
    Log.w( MySQLiteHelper.class.getName( ), "Upgrading database from version "
      + oldVersion + " to " + newVersion + ", which will destroy all old data" );
    db.execSQL( "DROP TABLE IF EXISTS" + TABLE_COMMENTS );
    onCreate( db );
  }
}