Data Storage and Persistence

Data Storage and Persistence

Data storage and persistence in Android involve techniques for saving and managing data in a way that it remains available across app sessions, system restarts, or even when the app is removed. Here’s a breakdown of key concepts and methods:

SharedPreferences

Purpose:

• SharedPreferences is used to store simple data such as user preferences or settings in key-value pairs.

Characteristics:

• Simplicity: Ideal for storing primitive data types (e.g., String, int, boolean).
• Private Storage: Data is private to the app and stored in XML files.

Use Cases:

• User settings (e.g., theme preferences, login state).
• Simple app configurations.

Implementation:

• Use SharedPreferences to save and retrieve data using SharedPreferences.Editor.

Internal and External Storage

Internal Storage:

• Purpose: Internal storage is used to store files privately within the app’s internal storage directory. Other apps cannot access these files.
• Characteristics: Secure and private to the app.
• Use Cases: Sensitive data, app-specific files (e.g., cached images, user-generated files).
• Implementation: Use file I/O APIs to write to and read from internal storage.

External Storage:

• Purpose: External storage is used to store files that can be accessed by other apps or the user. This includes both shared and non-shared storage.
• Characteristics: Files can be accessed by other apps and the user; however, sensitive data should be avoided here.
• Use Cases: Media files (e.g., photos, music), shared documents.
• Implementation: Requires permissions for access. Use File APIs to write to and read from external storage.

SQLite and Room Database

SQLite:

• Purpose: SQLite is a lightweight, relational database engine used for storing structured data in tables.
• Characteristics: Provides powerful query capabilities but requires manual management of database schema and queries.
• Use Cases: Complex data structures, relationships, or when performing complex queries.
• Implementation: Use SQLiteOpenHelper to manage database creation, version management, and CRUD operations.

Room Database:

• Purpose: Room is an abstraction layer over SQLite that simplifies database operations and provides compile-time checks.
• Characteristics: Eases the use of SQLite by using annotated classes and DAOs (Data Access Objects) to handle database operations.
• Use Cases: Efficient database management, avoiding boilerplate code, handling database migrations.
• Implementation: Define Entity classes, DAO interfaces, and a RoomDatabase abstract class. Use Room’s annotations to perform operations.