Ask for local notification permissions in AppDelegate

AppDelegate.cs

// Check for permissions
if (UIDevice.CurrentDevice.CheckSystemVersion (10, 0)) {
    // Ask the user for permission to get notifications on iOS 10.0+
    UNUserNotificationCenter.Current.RequestAuthorization (
        UNAuthorizationOptions.Alert | UNAuthorizationOptions.Badge | UNAuthorizationOptions.Sound,
        (approved, error) => {
            if (approved) {
                UNUserNotificationCenter.Current.Delegate = new UserNotificationCenterDelegate ();
            }
        });
} else if (UIDevice.CurrentDevice.CheckSystemVersion (8, 0)) {
    // Ask the user for permission to get notifications on iOS 8.0+
    var settings = UIUserNotificationSettings.GetSettingsForTypes (
        UIUserNotificationType.Alert | UIUserNotificationType.Badge | UIUserNotificationType.Sound,
        new NSSet ());

    UIApplication.SharedApplication.RegisterUserNotificationSettings (settings);
}

UserNotificationCenterDelegate.cs

using UserNotifications;

namespace LocalNotifications.iOS.Notifications
{
    public class UserNotificationCenterDelegate : UNUserNotificationCenterDelegate
    {
        public UserNotificationCenterDelegate()
        {
        }
    }
}