region service

        private readonly IRegionService _regionService;
            _regionService = new RegionService();
            _regionService.DisplayUserControl += _regionService_DisplayUserControl;

        private void _regionService_DisplayUserControl(object sender, UserControl e)
        {
            CloseUserControl();
            // Add new user control to content area
            contentArea.Children.Add(e);
        }

 private void LoadUserControl(string controlName)
        {
            _regionService.LoadUserControl(controlName);
}

 public class RegionService : IRegionService
    {
        public event EventHandler<UserControl> DisplayUserControl;


        public void LoadUserControl(string controlName)
        {
            Type ucType = null;
            UserControl uc = null;

            //if (ShouldLoadUserControl(controlName))
            //{
                // Create a Type from controlName parameter
                ucType = Type.GetType(controlName);
                if (ucType == null)
                {
                    MessageBox.Show("The Control: " + controlName
                                                    + " does not exist.");
                }
                else
                {
                    // Close current user control in content area
                    // NOTE: Optionally add current user control to a list
                    //       so you can restore it when you close the newly added one
                    //CloseUserControl();

                    // Create an instance of this control
                    uc = (UserControl)Activator.CreateInstance(ucType);

                    // Display control in content area
                    DisplayUserControl?.Invoke(this, uc);
                }
            //}
        }
    }

 public interface IRegionService
    {
        event EventHandler<UserControl> DisplayUserControl;
        void LoadUserControl(string controlName);
    }