Can't send an email from the app

Hello guys ! I am trying to send an email from my app. I am trying to do it with the DependencyService. For now I am implementing it for iOS only and I have the following warning : " ConsultantsApp.iOS[486:47185] Warning: Attempt to present on whose view is not in the window hierarchy! " . This is the code from my class:

public class IMailSender : UIViewController, MailSender
{

    MFMailComposeViewController mailController;

    public IMailSender()
    {

    }

    public void sendMail (string subject)
    {
        if (MFMailComposeViewController.CanSendMail) {
            mailController = new MFMailComposeViewController ();
            mailController.SetToRecipients (new string[]{"stefan@edenofapps.com"});
            mailController.SetSubject (subject);
            mailController.SetMessageBody ("this is a test", false);
            mailController.Finished += ( object s, MFComposeResultEventArgs args) => {
                Console.WriteLine (args.Result.ToString ());
                BeginInvokeOnMainThread (() => {
                    args.Controller.DismissViewController (true, null);
                });
            };
    };
        if (MFMailComposeViewController.CanSendMail) {
            this.PresentViewController (mailController, true, null);
        } else {
            new UIAlertView("Mail not supported", "Can't send mail from this device", null, "OK");
        }
    }
}

And this is my AppDelegate class:

    public override bool FinishedLaunching(UIApplication app, NSDictionary options)
    {
        Forms.Init();

        window = new UIWindow(UIScreen.MainScreen.Bounds);

        window.RootViewController = App.GetMainPage().CreateViewController();

        window.MakeKeyAndVisible();

        return true;
    }

}

Thanks in advance !