MvxAlertViewController.cs

public abstract class MvxAlertViewController<TViewModel> : MvxViewController<TViewModel>, IMvxAlertViewController
  where TViewModel : class, IMvxViewModel
{
  private const string ContentViewControllerKey = "contentViewController";

  private MvxIosViewPresenter _viewPresenter;
  private UIAlertController _alertController;

  public override string Title
  {
    get => _alertController.Title;
    set => _alertController.Title = value;
  }

  public string Message
  {
    get => _alertController.Message;
    set => _alertController.Message = value;
  }

  protected UITextField AddTextField()
  {
    if (_alertController.PreferredStyle != UIAlertControllerStyle.Alert)
    {
      return null;
    }

    var textField = default(UITextField);

    _alertController.AddTextField(view => textField = view);

    return textField;
  }

  protected UIAlertAction AddAction(ICommand command, string title, UIAlertActionStyle style, bool isPreferred)
  {
    var alertAction = UIAlertAction.Create(title, style, async _ =>
    {
      command.SafeExecute();

      await _viewPresenter.CloseModalViewController(_alertController, new MvxModalPresentationAttribute())
        .ConfigureAwait(false);
    });

    _alertController.AddAction(alertAction);

    if (isPreferred)
    {
      _alertController.PreferredAction = alertAction;
    }

    return alertAction;
  }

  public UIAlertController Wrap(MvxAlertPresentationAttribute attribute, MvxIosViewPresenter viewPresenter)
  {
    _viewPresenter = viewPresenter;

    _alertController = UIAlertController.Create(
      attribute.Title,
      attribute.Message,
      attribute.PreferredStyle
    );

    _alertController.SetValueForKey(this, new NSString(ContentViewControllerKey));

    var preferredContentSize = new CGSize(1, 1);

    PreferredContentSize = preferredContentSize;
    _alertController.PreferredContentSize = preferredContentSize;

    return _alertController;
  }
}