CaritasPWA/Shared/UserData.cs

using System.ComponentModel;
using System.Runtime.CompilerServices;

namespace CaritasPWA.Shared {
    // The class that stores the user settings
    public class UserData : INotifyPropertyChanged {
        private string firstname;
        private string lastname;

        public string Firstname {
            get => firstname; 
            set {
                firstname = value;
                RaisePropertyChanged();
            }
        }

        public string Lastname {
            get => lastname; 
            set {
                lastname = value;
                RaisePropertyChanged();
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void RaisePropertyChanged([CallerMemberName] string propertyName = null) {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}