# Codable & JSON Parsing (iOS)

> Codable protocol, JSONEncoder, JSONDecoder, custom keys, nested JSON, date strategies

- 20 interview questions
- Mid-Level
- [Interview Questions: iOS](https://sharpskill.dev/en/technologies/ios/interview-questions.md)

## 1. What is the Codable protocol in Swift?

**Answer**

Codable is a typealias combining Encodable and Decodable. It enables serialization and deserialization of Swift structures to/from JSON or other formats. It's the standard mechanism for handling JSON in iOS without external frameworks.

## 2. What is the difference between Encodable and Decodable?

**Answer**

Encodable serializes a Swift instance into JSON data (object to JSON). Decodable performs the reverse operation, converting JSON into a Swift instance. These protocols are orthogonal: a struct can implement one, the other, or both as needed.

## 3. What is the purpose of the CodingKeys enum during JSON decoding?

**Answer**

CodingKeys maps Swift properties to actual JSON keys. It handles naming mismatches between Swift code (camelCase) and JSON (snake_case). Without CodingKeys, property names must exactly match JSON keys.

## 17 more questions available

- How to create a JSONDecoder instance to decode JSON?
- What does JSONEncoder.encode() return after successful serialization?

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## Other iOS interview topics

- [Swift Basics](https://sharpskill.dev/en/technologies/ios/interview-questions/swift-basics.md): 25 questions, Junior
- [Swift Language Essentials](https://sharpskill.dev/en/technologies/ios/interview-questions/swift-language-essentials.md): 15 questions, Junior
- [UIKit Fundamentals](https://sharpskill.dev/en/technologies/ios/interview-questions/uikit-fundamentals.md): 18 questions, Junior
- [UIViewController Lifecycle](https://sharpskill.dev/en/technologies/ios/interview-questions/uiviewcontroller-lifecycle.md): 20 questions, Junior
- [UserDefaults & Keychain](https://sharpskill.dev/en/technologies/ios/interview-questions/userdefaults-keychain.md): 20 questions, Junior
- [Application Lifecycle](https://sharpskill.dev/en/technologies/ios/interview-questions/app-lifecycle.md): 20 questions, Junior
- [Auto Layout & Constraints](https://sharpskill.dev/en/technologies/ios/interview-questions/auto-layout-constraints.md): 24 questions, Mid-Level
- [UITableView & UICollectionView](https://sharpskill.dev/en/technologies/ios/interview-questions/uitableview-uicollectionview.md): 25 questions, Mid-Level
- [SwiftUI Basics](https://sharpskill.dev/en/technologies/ios/interview-questions/swiftui-basics.md): 18 questions, Mid-Level
- [SwiftUI State Management](https://sharpskill.dev/en/technologies/ios/interview-questions/swiftui-state-management.md): 22 questions, Mid-Level
- [SwiftUI Navigation](https://sharpskill.dev/en/technologies/ios/interview-questions/swiftui-navigation.md): 18 questions, Mid-Level
- [Networking & URLSession](https://sharpskill.dev/en/technologies/ios/interview-questions/networking-urlsession.md): 20 questions, Mid-Level
- [Core Data](https://sharpskill.dev/en/technologies/ios/interview-questions/core-data.md): 22 questions, Mid-Level
- [Protocol Oriented Programming](https://sharpskill.dev/en/technologies/ios/interview-questions/protocol-oriented-programming.md): 20 questions, Mid-Level
- [MVVM Architecture](https://sharpskill.dev/en/technologies/ios/interview-questions/mvvm-architecture.md): 20 questions, Mid-Level
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- [Unit Testing & XCTest](https://sharpskill.dev/en/technologies/ios/interview-questions/unit-testing-xctest.md): 20 questions, Mid-Level
- [UI Testing](https://sharpskill.dev/en/technologies/ios/interview-questions/ui-testing.md): 18 questions, Mid-Level
- [Xcode & Build System](https://sharpskill.dev/en/technologies/ios/interview-questions/xcode-build-system.md): 16 questions, Mid-Level
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- [Combine Framework](https://sharpskill.dev/en/technologies/ios/interview-questions/combine-framework.md): 24 questions, Senior
- [Concurrency & async/await](https://sharpskill.dev/en/technologies/ios/interview-questions/concurrency-async-await.md): 26 questions, Senior
- [iOS Design Patterns](https://sharpskill.dev/en/technologies/ios/interview-questions/ios-design-patterns.md): 24 questions, Senior
- [Performance Optimization](https://sharpskill.dev/en/technologies/ios/interview-questions/performance-optimization.md): 22 questions, Senior
- [Security & Encryption](https://sharpskill.dev/en/technologies/ios/interview-questions/security-encryption.md): 20 questions, Senior
- [SwiftUI Advanced](https://sharpskill.dev/en/technologies/ios/interview-questions/swiftui-advanced.md): 22 questions, Senior
- [iOS Application Architecture](https://sharpskill.dev/en/technologies/ios/interview-questions/ios-app-architecture.md): 22 questions, Senior

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