LoginRegister ViewModel

namespace SpaceTakeover
{
    public class LoginData : ModelBase
    {

        public override string this[string columnName]
        {
            get { return null; }
        }
        private string username = String.Empty;

        public string Username
        {
            get { return username; }
            set { username = value; NotifyOnPropertyChanged("Username"); }
        }

        private string password = String.Empty;

        public string Password
        {
            get { return password; }
            set { password = value; NotifyOnPropertyChanged("Password"); }
        }
    }
    public class RegistrationData : ModelBase
    {

        public override string this[string columnName]
        {
            get
            {
                string errorString = null;
                if (columnName == "Username")
                {
                    if (String.IsNullOrEmpty(Username) || Username.Length < 3)
                    {
                        errorString = "Username must be at least 3 characters.";
                    }
                }
                if (columnName == "ReEnterPassword")
                {
                    if (ReEnterPassword != Password)
                    {
                        errorString = "Passwords do not match.";
                    }
                }
                if (columnName == "Email")
                {
                    if (!System.Text.RegularExpressions.Regex.IsMatch(Email, @"(\w+@[a-zA-Z_]+?\.[a-zA-Z]{2,6})"))//If email is syntatically valid
                    {
                        errorString = "Email is in an invalid format.";
                    }
                }
                return errorString;
            }
        }

        private string username = String.Empty;

        public string Username
        {
            get { return username; }
            set { username = value; NotifyOnPropertyChanged("Username"); }
        }

        private string password = String.Empty;

        public string Password
        {
            get { return password; }
            set { password = value; NotifyOnPropertyChanged("Password"); }
        }

        private string rePassword = String.Empty;

        public string ReEnterPassword
        {
            get { return rePassword; }
            set { rePassword = value; NotifyOnPropertyChanged("ReEnterPassword"); }
        }

        private string betaKey = String.Empty;

        public string BetaKey
        {
            get { return betaKey; }
            set { betaKey = value; NotifyOnPropertyChanged("BetaKey"); }
        }

        private string email = String.Empty;

        public string Email
        {
            get { return email; }
            set { email = value; NotifyOnPropertyChanged("Email"); }
        }

        private bool registerEnabled = true;

        public bool RegisterEnabled
        {
            get { return registerEnabled; }
            set { registerEnabled = value; NotifyOnPropertyChanged("RegisterEnabled"); }
        }
    }
    public class LoginCommand : CommandBase
    {
        private LoginRegisterClient client;

        public LoginCommand()
        {
            client = new LoginRegisterClient();
            Text = "Login";
        }

        public LoginCommand(LoginRegisterClient remoteClient)
        {
            client = remoteClient;
        }

        public override bool CanExecute(object parameter)
        {
            return parameter is TextBlock;
        }

        public override void Execute(object parameter)
        {
            TextBlock errorBlock = parameter as TextBlock;
            client.LoginCompleted += GenerateLoginCompletedDelegate(errorBlock);
        }
        private EventHandler<LoginCompletedEventArgs> GenerateLoginCompletedDelegate(TextBlock errorBlock)
        {
            return (object sender, LoginCompletedEventArgs e) =>
                {
                    bool loginSuccess = e.Result;
                    if (!loginSuccess)
                    {
                        errorBlock.Text = "Login Failed.";
                    }
                    else
                    {
                        FrameworkElement ctrl = errorBlock;
                        while (!((ctrl = ctrl.Parent as FrameworkElement) is PageSwitcher))
                        {
                            if (ctrl != null)
                            {
                                PageSwitcher ps = ctrl as PageSwitcher;
                                ps.Navigate(new SelectUniversePage());
                            }
                        }
                    }
                };
        }
    }
    public class RegisterCommand : CommandBase
    {
        private LoginRegisterClient client;

        public RegisterCommand()
        {
            client = new LoginRegisterClient();
            Text = "Register";
        }

        public RegisterCommand(LoginRegisterClient remoteClient)
        {
            client = remoteClient;
        }

        public override bool CanExecute(object parameter)
        {
            return parameter is TextBlock;
        }

        public override void Execute(object parameter)
        {
            TextBlock errorBlock = parameter as TextBlock;
            client.RegisterCompleted += GenerateRegistrationCompletedDelegate(errorBlock);
        }
        private EventHandler<RegisterCompletedEventArgs> GenerateRegistrationCompletedDelegate(TextBlock errorBlock)
        {
            return (object sender, RegisterCompletedEventArgs e) =>
                {
                    bool loginSuccess = e.Result;
                    if (!loginSuccess)
                    {
                        errorBlock.Text = "Registration Failed.";
                    }
                    else
                    {
                        FrameworkElement ctrl = errorBlock;
                        while (!((ctrl = ctrl.Parent as FrameworkElement) is PageSwitcher))
                        {
                            if (ctrl != null)
                            {
                                PageSwitcher ps = ctrl as PageSwitcher;
                                ps.Navigate(new SelectUniversePage());
                            }
                        }
                    }
                };
        }
    }
    public class ViewModelLoginRegister
    {
        private LoginRegisterClient client = new LoginRegisterClient();
        public LoginCommand LoginCmd { get; set; }
        public LoginData LoginInfo { get; set; }
        public RegistrationData RegistrationInfo { get; set; }
        public RegisterCommand RegisterCmd { get; set; }
        public ViewModelLoginRegister()
        {
            LoginInfo = new LoginData();
            RegistrationInfo = new RegistrationData();
            LoginCmd = new LoginCommand(client);
            RegisterCmd = new RegisterCommand(client);
        }
    }
}