I want to know what is use of onCreate() and onUpgrade() method of SQLiteOpenHelper.
And when the onCreate() and onUpgrade() method is called.?
onUpgrade() callbacks are invoked when the database is actually opened, for example by a call to
getWritableDatabase(). The database is not opened when the database helper object itself is created.
onCreate() is only run when the database file did not exist and was just created. If
onCreate() returns successfully (doesn't throw an exception), the database is assumed to be created with the requested version number. As an implication, you should not catch
onUpgrade() is only called when the database file exists but the stored version number is lower than requested in constructor. The
onUpgrade() should update the table schema to the requested version.
When changing the table schema in code (
onCreate()), you should make sure the database is updated. Two main approaches:
Delete the old database file so that
onCreate() is run again. This is often preferred at development time where you have control over the installed versions and data loss is not an issue. Some ways to to delete the database file:
Uninstall the application. Use the application manager or
adb uninstall your.package.name from shell.
Clear application data. Use the application manager.
Increment the database version so that
onUpgrade() is invoked. This is slightly more complicated as more code is needed.
For development time schema upgrades where data loss is not an issue, you can just use
execSQL("DROP TABLE IF EXISTS <tablename>") in to remove your existing tables and call
onCreate() to recreate the database.
For released versions, you should implement data migration in
onUpgrade() so your users don't lose their data.