Notes on Solid with Android - Video 2

Introduction

• Presented by: Anil Deshpande
• Focus: Refactoring code in Android, specifically looking beyond the model to the repository.

Recap of Previous Video

• Refactored DAO, model, and app database with the database provider.
• Encouraged viewers to revisit the previous video for context.

Current Focus

• Refactoring the Country Repository.

Country Repository Overview

• Implements iCountryRepository.
• Initial code commented out for filtering countries.

Dispatcher Usage

• All functions currently use withContext(Dispatchers.IO).
• Dispatcher: Controls where the suspend function executes (in this case on IO dispatcher).
• OCP Violation: Using an explicit dispatcher in multiple locations.

Proposed Changes

• Introduce a dispatcher as an argument to the CountryRepository class.
• Create a variable dispatcher of type CoroutineDispatcher to be used throughout the class.

Implementing Filter Criteria

• Current filtering methods are rigid (e.g., filtering by continent or drive side).
• Need for flexibility to add more filters without modifying existing code.

Open/Closed Principle (OCP)

• Code should be open for extension but closed for modification.
• Goal: Introduce new filter criteria without altering existing code.

Strategy Pattern Explained

• Analogy of cooking: Cutting tasks vary based on the object (vegetable, bread, pizza).
• In coding, filtering should vary depending on the criteria (continent, drive side, language).

Implementation Steps

1. Create an Interface:
   • Define a FilterCriteria interface with a suspend fun filter(countries: List<Country>): List<Country>.
2. Implement Filter Criteria Classes:
   • FilterByContinent: Implements filtering by continent.
   • FilterByDriveSide: Implements filtering by drive side.
   • Future filters can be added by creating new classes that implement the FilterCriteria interface.

Updating the Repository

• Enable the filterCountries function in the CountryRepository.
• It will receive a FilterCriteria object, which decides how to filter the list of countries.

Next Steps

• Plan to refactor the ViewModel next.

Conclusion

• Summary of refactoring repository to adhere to SOLID principles.
• Encouragement to engage with the video: like, comment, share, and subscribe.
• Closing remarks: Take care and goodbye.