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SOLID - Architecture and Architectural Decisions Rivu Chakraborty 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] https://topmate.io/rivu

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● India’s first GDE (Google Developer Expert) for Kotlin ● More than 12 years in the Industry ● Mobile Architect @ JioCinema ● Previously ○ Byju’s ○ Paytm ○ Gojek ○ Meesho ● Author (wrote multiple Kotlin books) ● Speaker ● Community Person ● Entrepreneur (?) 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Who am I? 󰞦

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SOLID

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SOLID Single Responsibility

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does Single Responsibility Mean 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] One class/function/object should focus on a single thing

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does Single Responsibility Mean 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Let’s say you have a viewmodel, and along with maintaining the state, the viewmodel is doing business logic. Is it Single Responsibility?

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does Single Responsibility Mean 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] There’s a Repository in our app, which is fetching data from the server and saving it in the local database while passing it onto the presentation layer (VM). Is it Single Responsibility?

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SOLID Open-closed principle

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] classes, modules, and functions should be open for extension but closed for modification.

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] You have chat app. You only had text chat till now, you’re adding support for image sharing. So you add a flag (isImage) in your Chat class. Is it following OCP?

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Same example, you added an enum on MediaType instead of the boolean flag Is it following OCP?

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Same example, you added an enum on MediaType instead of the boolean flag. To add various data (like image url etc), you have to keep editing the Message class. Is it following OCP?

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] In the same chat app, you’re now adding Emoji 😃 support in Text Messages You Edited the TextMessage Class to do this. Is it following OCP?

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SOLID Liskov Substitution Principle

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Objects of a superclass shall be replaceable with objects of its subclasses without breaking the application

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Same Example. You have chat app. You only had text chat till now, you’re adding support for various other types of messages. Instead of creating enum/flags. You decided to extend the existing Message class. Is it following Liskov Substitution?

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SOLID Interface Segregation

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] No code should be forced to depend on methods it does not use. In other words, child classes should not be forced to implement/extend super class methods that it doesn’t require.

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Same Example. You have chat app. You only had text chat till now, you’re adding support for various other types of messages. You decided to better create an interface. Interface code in next slide.

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] interface IMessage { fun getMessageText(): String fun getMessageType(): MessageType fun getMediaUrl(): Url fun getMediaPreviewBase64(): Base64 fun getAudioVideoCodec(): Codec } //Is it following Interface Segregation?

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SOLID Dependency Inversion

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] What Does it Mean? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] A class that uses a dependency, should not create it

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Dependency Inversion / Inversion of Control 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] It’s not only Dependency Injection

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Dependency Inversion / Inversion of Control 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Dependency Injection ● Constructor Injection ● Service Locator

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Dependency Injection 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Injecting a Dependency to a class / object at creation time, without any additional code in the class

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Dependency Injection 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Injecting a Dependency to a class / object at creation time, without any additional code in the class ● It’s mostly done with Annotation processors in Java / JVM

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Dependency Injection 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Injecting a Dependency to a class / object at creation time, without any additional code in the class ● It’s mostly done with Annotation processors in Java / JVM ● Example: Dagger / Hilt / Spring DI etc / Kotlin-Inject

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Constructor Injection 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Done with passing parameters in the constructor

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Constructor Injection 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Done with passing parameters in the constructor ● It’s also a type of Service Locator

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Constructor Injection 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Done with passing parameters in the constructor ● It’s also a type of Service Locator ● Vanilla implementation of Dependency Inversion is often done with Constructor Injection

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Service Locator 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Where a class has to request for a Dependency, but doesn’t directly create it

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Service Locator 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Where a class has to request for a Dependency, but doesn’t directly create it ● Example is Koin, where it uses Delegation to create dependencies

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🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] Which one is Better? 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] ● Dependency Injection ● Constructor Injection ● Service Locator

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Thank You Rivu Chakraborty 🌐https://www.rivu.dev/ youtube.com/@rivutalks @rivuchakraborty @[email protected] https://topmate.io/rivu