Storing and Retrieving Data in Android with SQLite Quiz

Storing and Retrieving Data in Android

• SQLite is a relational database technology used in Android apps, included with the Android system.
• To create a database in Android, a subclass of SQLiteOpenHelper is created, which provides functionality to create a database and calls a function that can be overridden by the derived class.

Creating a Database in Android

• SQLiteOpenHelper constructor accepts four arguments: Context, Name, Factory, and Version.
• The Version number is used to identify if there is an upgrade or downgrade of the database.
• onCreate() method is called when creating the database, and it is passed the SQLiteDatabase reference.
• onUpgrade() method is called when the database is upgraded, and it is passed the SQLiteDatabase, oldVersion, and newVersion.

Writing and Reading Data

• To write data to the database, use getWritableDatabase().
• To read data from the database, use getReadableDatabase().
• The insert function on the SQLiteDatabase class is used to add values to the database, taking three arguments: table name, column name, and ContentValues.
• Running a raw SQL query returns a cursor that points to all the rows found by the query.

Working with Content Providers

• Content Providers are central repositories that store and share application data in Android.
• Content Providers store data in several ways/formats and facilitate secure access and modification by other applications.
• Content Providers have permissions to grant or restrict access to data.

Content URI

• Content URI is a key concept in Content Providers, used to access data from a Content Provider.
• The Content URI consists of: content://, authority, optionalPath, and optionalID.
• The authority signifies the name of the Content Provider, and the optionalPath specifies the type of data provided.

Operations in Content Provider

• Four fundamental operations are possible in Content Provider: Create, Read, Update, and Delete (CRUD operations).
• These operations are used to create, fetch, modify, and delete data from the Content Provider.

Creating a Content Provider

• To create a Content Provider, follow these steps:
  • Create a class that extends the ContentProvider base class.
  • Define a content provider URI address.
  • Create a database to store the application data.
  • Implement the six abstract methods of ContentProvider class.
  • Register the Content Provider in AndroidManifest.xml file using the provider tag.

Six Abstract Methods of ContentProvider Class

• query(): fetches data from the desired table and returns a cursor object.
• insert(): inserts a new row in the database and returns the content URI of the inserted row.
• update(): updates the fields of an existing row and returns the number of rows updated.
• delete(): deletes existing rows and returns the number of rows deleted.
• getType(): returns the MIME type of data to the given Content URI.
• onCreate(): initializes the Content Provider when it is created.