Chapter 26:public abstract class SQLiteOpenHelper

public abstract class

SQLiteOpenHelper

extends Object

java.lang.Object
↳	android.database.sqlite.SQLiteOpenHelper

Class Overview

A helper class to manage database creation and version management.
You 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. Transactions are used to make sure the database is always in a sensible state.
This class makes it easy for ContentProvider implementations to defer opening and upgrading the database until first use, to avoid blocking application startup with long-running database upgrades.

Public Constructors

public SQLiteOpenHelper (Context context, String name, SQLiteDatabase.CursorFactory factory, int version)

Since: API Level 1
Create a helper object to create, open, and/or manage a database. This method always returns very quickly. The database is not actually created or opened until one of getWritableDatabase() or getReadableDatabase() is called.

Parameters

context	to use to open or create the database
name	of the database file, or null for an in-memory database
factory	to use for creating cursor objects, or null for the default
version	number of the database (starting at 1); if the database is older, onUpgrade(SQLiteDatabase, int, int) will be used to upgrade the database; if the database is newer, onDowngrade(SQLiteDatabase, int, int) will be used to downgrade the database

public SQLiteOpenHelper (Context context, String name, SQLiteDatabase.CursorFactory factory, int version, DatabaseErrorHandler errorHandler)

Since: API Level 11
Create a helper object to create, open, and/or manage a database. The database is not actually created or opened until one of getWritableDatabase() or getReadableDatabase() is called.
Accepts input param: a concrete instance of DatabaseErrorHandler to be used to handle corruption when sqlite reports database corruption.

Parameters

context	to use to open or create the database
name	of the database file, or null for an in-memory database
factory	to use for creating cursor objects, or null for the default
version	number of the database (starting at 1); if the database is older, onUpgrade(SQLiteDatabase, int, int) will be used to upgrade the database
errorHandler	the DatabaseErrorHandler to be used when sqlite reports database corruption.

Public Methods

public synchronized void close ()

Since: API Level 1
Close any open database object.

public String getDatabaseName ()

Since: API Level 14
Return the name of the SQLite database being opened, as given tp the constructor.

public synchronized SQLiteDatabase getReadableDatabase ()

Since: API Level 1
Create and/or open a database. This will be the same object returned by getWritableDatabase() unless some problem, such as a full disk, requires the database to be opened read-only. In that case, a read-only database object will be returned. If the problem is fixed, a future call to getWritableDatabase() may succeed, in which case the read-only database object will be closed and the read/write object will be returned in the future.
Like getWritableDatabase(), this method may take a long time to return, so you should not call it from the application main thread, including from ContentProvider.onCreate().

Returns

• a database object valid until getWritableDatabase() or close() is called.
  

Throws

SQLiteException	if the database cannot be opened

public synchronized SQLiteDatabase getWritableDatabase ()

Since: API Level 1
Create and/or open a database that will be used for reading and writing. The first time this is called, the database will be opened and onCreate(SQLiteDatabase), onUpgrade(SQLiteDatabase, int, int) and/or onOpen(SQLiteDatabase) will be called.
Once opened successfully, the database is cached, so you can call this method every time you need to write to the database. (Make sure to call close() when you no longer need the database.) Errors such as bad permissions or a full disk may cause this method to fail, but future attempts may succeed if the problem is fixed.
Database upgrade may take a long time, you should not call this method from the application main thread, including from ContentProvider.onCreate().

Returns

• a read/write database object valid until close() is called
  

Throws

SQLiteException	if the database cannot be opened for writing

public abstract void onCreate (SQLiteDatabase db)

Since: API Level 1
Called when the database is created for the first time. This is where the creation of tables and the initial population of the tables should happen.

Parameters

db	The database.

public void onDowngrade (SQLiteDatabase db, int oldVersion, int newVersion)

Since: API Level 11
Called when the database needs to be downgraded. This is stricly similar to onUpgrade() method, but is called whenever current version is newer than requested one. However, this method is not abstract, so it is not mandatory for a customer to implement it. If not overridden, default implementation will reject downgrade and throws SQLiteException

Parameters

db	The database.
oldVersion	The old database version.
newVersion	The new database version.

public void onOpen (SQLiteDatabase db)

Since: API Level 1
Called when the database has been opened. The implementation should check isReadOnly() before updating the database.

Parameters

db	The database.

public abstract void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion)

Since: API Level 1
Called when the database needs to be upgraded. The implementation should use this method to drop tables, add tables, or do anything else it needs to upgrade to the new schema version.
The SQLite ALTER TABLE documentation can be found here. If you add new columns you can use ALTER TABLE to insert them into a live table. If you rename or remove columns you can use ALTER TABLE to rename the old table, then create the new table and then populate the new table with the contents of the old table.

Parameters

db	The database.
oldVersion	The old database version.
newVersion	The new database version.

http://www.vogella.de/articles/AndroidSQLite/article.html

http://developer.android.com/reference/android/database/sqlite/SQLiteOpenHelper.html

http://www.codeproject.com/Articles/26869/Database-Helper-v-2-0-0