Android_unit_6

6.1 Content Providers

Content Providers are one of the fundamental components of Android that allow applications to share data with each other. They provide a standard interface to access and manage data stored in a central repository.
A Content Provider acts as a mediator between the application and the data source, which can be a SQLite database, a file, or even a remote server. The Content Provider provides a set of methods to query, insert, update, and delete data in a consistent way, regardless of the underlying data source.

To use a Content Provider in your application, you need to follow these steps:

1. Define the Content Provider

To define a Content Provider, you need to create a class that extends the android.content.ContentProvider class and implement its abstract methods. The most important methods are query(), insert(), update(), and delete(), which define how the data is accessed and manipulated.

2. Register the Content Provider

To use the Content Provider in your application, you need to register it in the AndroidManifest.xml file.

3. Access the Content Provider

To access the data provided by the Content Provider, you need to use a ContentResolver object. The ContentResolver object provides a set of methods to query, insert, update, and delete data using the Content Provider.

6.2 SQLite Programming

SQLite is a lightweight relational database management system (RDBMS) that is used by Android to manage local data storage. It provides a simple and efficient way to store structured data in an application.
In Android, SQLite is implemented as a part of the Android framework, so developers do not need to download or install it separately. The Android framework provides several classes and interfaces to work with SQLite databases.
Here's an overview of SQLite programming in Android:

1. Creating a database: To create a new SQLite database in Android, you need to create a subclass of the SQLiteOpenHelper class. This class provides methods to create and upgrade the database.

2. Defining a table: To define a table in the database, you need to create a SQL statement that describes the table's structure. You can define the columns, data types, primary key, foreign key constraints, etc. The SQL statement is executed using the SQLiteDatabase object.

3. Inserting data: To insert data into a table, you need to create a ContentValues object that contains the data to be inserted. You then call the insert() method of the SQLiteDatabase object, passing in the table name and the ContentValues object.

4. Querying data: To query data from a table, you need to create a SQL SELECT statement that specifies the columns to be returned and the selection criteria. You can execute the SQL statement using the SQLiteDatabase object's query() method, which returns a Cursor object containing the results.

5. Updating data: To update data in a table, you need to create a ContentValues object that contains the new values for the columns to be updated. You then call the update() method of the SQLiteDatabase object, passing in the table name, the ContentValues object, and the selection criteria.

6. Deleting data: To delete data from a table, you need to create a SQL DELETE statement that specifies the selection criteria. You can execute the SQL statement using the SQLiteDatabase object's delete() method, passing in the table name and the selection criteria.

6.3 SQLiteOpenHelper

SQLiteOpenHelper is a helper class provided by Android to manage the creation and upgrade of an SQLite database. It provides a set of methods to create, upgrade, and open a database. It also provides a way to execute SQL statements on the database.

SQLiteOpenHelper is an abstract class provided by the Android framework to manage database creation and version management in SQLite databases. It provides a set of methods that can be overridden to create and upgrade the database schema.

To use SQLiteOpenHelper, you need to create a subclass of it and implement the onCreate() and onUpgrade() methods. The onCreate() method is called when the database is first created and is used to define the database schema, including the tables, columns, and indexes. The onUpgrade() method is called when the database schema needs to be upgraded, typically when the app is upgraded to a new version that requires a different database schema.

Here's an example of how to create a subclass of SQLiteOpenHelper:

public class MyDatabaseHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "mydatabase.db";
private static final int DATABASE_VERSION = 1;

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

@Override
public void onCreate(SQLiteDatabase db) {
// Define the database schema here
db.execSQL("CREATE TABLE mytable (_id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, age INTEGER);");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// Upgrade the database schema here
db.execSQL("DROP TABLE IF EXISTS mytable;");
onCreate(db); }}

6.4 SQLiteDatabse

SQLiteDatabase is a class provided by the Android framework that provides a set of methods to interact with SQLite databases. It is used to perform database operations such as insert, update, delete, and query.
To use SQLiteDatabase, you need to obtain an instance of it by calling the getWritableDatabase() or getReadableDatabase() method on an instance of SQLiteOpenHelper.
SQLiteDatabase is a class in the Android framework that provides a set of methods to interact with SQLite databases. SQLite is a lightweight, embedded, relational database engine that is built into Android.
To use SQLiteDatabase , you need to create an instance of it by calling either getWritableDatabase() or getReadableDatabase() on an instance of SQLiteOpenHelper . getWritableDatabase() returns a SQLiteDatabase object that allows you to perform write operations on the database, while getReadableDatabase() returns a SQLiteDatabase object that allows you to perform read operations on the database.
SQLiteDatabase provides methods for executing SQL statements, inserting, updating, and deleting rows in tables, and querying the database.

6.5 Cursor

In Android, a Cursor is an interface that provides random read-write access to the result set returned by a database query. It's commonly used with SQLite databases to read data from tables.
When you query a database using SQLiteDatabase.query() or SQLiteDatabase.rawQuery(), a Cursor object is returned that represents the result set of the query. The Cursor provides methods for navigating the result set, retrieving individual column values, and getting metadata about the result set, such as the number of rows and columns.

Some of the most commonly used methods in Cursor include:

• moveToFirst(),moveToLast(),moveToNext(),moveToPrevious(): Move the cursor to the first, last, next, or previous row in the result set, respectively.
• getColumnIndex(), getColumnIndexOrThrow(): Get the index of a column by name. getColumnIndex() returns -1 if the column doesn't exist, while getColumnIndexOrThrow() throws an IllegalArgumentException.
• getString(), getInt(), getLong(), getDouble(), getBlob(): Get the value of a column in the current row as a String, int, long, double, or byte array, respectively.
• getCount(): Get the number of rows in the result set.
• close(): Close the Cursor and release any resources associated with it.

6.6 Searching for content

In Android, you can use Content Providers to search for content across multiple applications and data sources. Content Providers are a powerful mechanism for sharing data between applications and allow you to perform queries and access data from different sources using a unified API.

To search for content, you can use the ContentResolver class, which is the primary interface for accessing a Content Provider. ContentResolver provides a set of methods for querying the Content Provider and retrieving results.