How did you implement the Dependency Injection mechanism in your projects?

In my iOS projects, I have implemented Dependency Injection (DI) to improve code modularity and testability. I usually used constructor injection, where dependencies are passed through the class initializer. For example, if I have a ViewModel class that depends on an APIService, I pass this service via the initializer:

class APIService {
    func fetchData() { /* ... */ }
}

class ViewModel {
    private let apiService: APIService

    init(apiService: APIService) {
        self.apiService = apiService
    }

    func loadData() {
        apiService.fetchData()
    }
}

// Usage
let service = APIService()
let viewModel = ViewModel(apiService: service)

I also used Property Injection, where dependencies are set through properties, and sometimes employed a Service Locator for centralized dependency management, but I tried to avoid it due to testing difficulties. In large projects, I used DI containers, such as Swinject, for automatic dependency resolution.