Dependency Injection in Swift

What is the use of dependency injection? | Sun 6 May 18

3 min readMay 18, 2018

Dependency Injection in Swift you can avoid Singleton Pattern and make more testable code with loose coupling.

Initially, I also don’t know about Dependency Injection when I have followed some standard coding pattern then I realize should I need to go Dependency Injection. At the beginning stage no one perfect by the working on real-life projects and facing problems then we learn the new things.

Then I have started adding Dependency Injection inside my projects then I got understanding its pretty easy to use. Most of the place I have stared avoiding Singleton Pattern.

What is the use of dependency injection?

By using dependency injection we can make more testable, more simple code we can write. Only we need to pass dependency through object initialization. Every class has its own responsibility for injecting dependency through the object.

Let’s see the without dependency injection code -

This is the normal singleton class which we are using here.

class DataManager{
    
    static let shared = DataManager()
    var delegate: ResponseHandler?
    
    private init(){}
    
    func requestForData(){
        //Code Process
        ...
    }
}

How to use this class

class ViewController: UIViewController, ResponseHandler {
  
  override func viewDidLoad() {
    super.viewDidLoad()    DataManager.shared.delegate = self
    DataManager.shared.requestForData()
  }}

With the use of Dependency Injection

class DataManager{
    
    private var delegate: ResponseHandler    //injecting here dependency
    init(delegate: ResponseHandler) {
         self.delegate = delegate
    }
    
    func requestForData(){
        //Code Process
        ...
    }
}

How to use this class

class HomeViewController: UIViewController, ResponseHandler {
  
  //Use the class with self-executing closure
  lazy var dataManager: DataManager = {
       let manager = DataManager(delegate: self)
       return manager
  }()  override func viewDidLoad() {
    super.viewDidLoad()
  }}

Passing dependency through the another ViewController

Now we have done small changes in current class.

class HomeViewController: UIViewController, ResponseHandler {
   
   var dataManager: DataManager?   override func viewDidLoad() {
     super.viewDidLoad()
   }}

coming this class from the another ViewController -

class ViewController: UIViewController{
  //MARK: - Navigation
  func moveToHomeController(){
     guard let homeView =
     self.storyboard?.instantiateViewController(withIdentifier:
                      "HomeViewController") as? HomeViewController
          else { print("View controller not found")
               return
          }
   //Passing here dependency 
   homeView.dataManager = DataManager(delegate: homeView.self)
   navigationController?.pushViewController(homeView, animated:   
   true)
  }
}

or through Segue

class ViewController: UIViewController{
    //MARK: - Navigation   
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
     if segue.identifier == homeViewControllerIdentifier,
     let homeView = segue.destination as? HomeViewController {
         homeView.dataManager = DataManager(delegate: homeView.self)
      }
    }
}

Dependency with Method injection

class APIManager{   func requestUserDetails(_ request: Request, database: DataManager, track: TrackDetails) -> ResponseManager? {
       ...
   }
}

Conclusion

Here we got understanding for Dependency Injection for manage more testable and distributed inside your code. In this part, we have covered how to pass single dependency to multiple dependency injections.
One more important thing I have covered in this part for pass dependency through the one view controller to another view controller. It’s pretty easy to use inside your code.

We also got one more thing here how to get confirm protocol delegate inside your code.

Thanks for reading 🙌🏼

If you having any query regarding this tutorial ? Twitter me: @Anand