Dependency injection in iOS Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is dependency injection in simple terms?

Dependency injection means giving an object what it needs instead of letting it create those things itself. It helps keep code clean and easy to change.

beginner

Why is dependency injection useful in iOS Swift apps?

It makes testing easier because you can swap real parts with fake ones. It also helps organize code so parts don’t depend too much on each other.

intermediate

What are the common ways to do dependency injection in Swift?

You can inject dependencies through initializer methods, by setting properties after creating an object, or by using a dependency container that provides needed parts.

beginner

Show a simple Swift example of initializer injection.

```swift
protocol Service {
  func doWork()
}

class RealService: Service {
  func doWork() { print("Working") }
}

class Client {
  let service: Service
  init(service: Service) {
    self.service = service
  }
  func start() {
    service.doWork()
  }
}

let service = RealService()
let client = Client(service: service)
client.start() // prints "Working"
```

intermediate

What problem does dependency injection solve compared to creating dependencies inside a class?

It avoids tight coupling, so classes don’t depend on specific implementations. This makes code easier to change, test, and reuse.

What is the main goal of dependency injection?

A To make objects create their own dependencies

B To give objects their dependencies from outside

C To hide dependencies inside methods

D To remove all dependencies

Dependency injection means providing dependencies from outside, not creating them inside.

Which of these is NOT a common way to inject dependencies in Swift?

A Method injection

B Property injection

C Inheritance injection

D Initializer injection

Inheritance injection is not a standard term or method for dependency injection.

Why does dependency injection help with testing?

A It hides bugs automatically

B It makes code run faster

C It removes the need for tests

D It allows replacing real parts with fake ones easily

Dependency injection lets you swap real dependencies with mocks or fakes for testing.

In the example: `init(service: Service)`, what is happening?

A Dependency is injected via initializer

B Dependency is created inside the class

C Dependency is ignored

D Dependency is deleted

The service is passed into the class through the initializer, which is initializer injection.

What does tight coupling mean in code?

A Classes depend too much on specific implementations

B Classes are independent and flexible

C Classes have no dependencies

D Classes are loosely connected

Tight coupling means classes rely heavily on specific details, making changes harder.

Explain dependency injection and why it is helpful in iOS Swift development.

Think about how giving objects what they need from outside helps keep code clean.

Describe how you would use initializer injection in a Swift class with a simple example.

Remember the example with a service protocol and a client class.