AppDelegate.cs

[Register("AppDelegate")]
public class AppDelegate : UIApplicationDelegate
{
  
  private void LoadDependencies()
  {
    // Load dependencies in methods that run once per run of the application
    IDependencyService serviceLocator = DependencyService.Instance;
    
    if (null == serviceLocator.GetService<ILoginPresenter) 
    {
      ILoginPresenter presenter = GetPresenter();
      serviceLocator.AddService(presenter, typeof(ILoginPresenter));
    }
    
    // Load other presenters
    ...
    
  }
  
  private ILoginPresenter GetPresenter()
  {
    // return presenter that supports all features of the current device
    ...
  }
}

// LoginViewController
public partial class LoginViewController : UIViewController
{
  private ILoginPresenter _loginPresenter = null;
  
  public override void ViewDidLoad()
  {
    base.ViewDidLoad();
    
    // Load presenter
    _loginPresenter = DependencyService.Instance.LoadService<ILoginPresenter>();
  }
}