Open Child Window in MVVM environment

namespace WindowWithMVVM.LoginUI
{
    using System;
    using System.ComponentModel.DataAnnotations;
    using System.ServiceModel.DomainServices.Client;
    using System.ServiceModel.DomainServices.Client.ApplicationServices;
    using WindowWithMVVM.Web.Resources;

    /// <summary>
    /// This internal entity is used to ease the binding between the UI controls (DataForm and the label displaying a validation error) and the log on credentials entered by the user.
    /// </summary>
    public class LoginInfo : ComplexObject
    {
        private string userName;
        private bool rememberMe;
        private LoginOperation currentLoginOperation;

        /// <summary>
        /// Gets and sets the user name.
        /// </summary>
        [Display(Name = "UserNameLabel", ResourceType = typeof(RegistrationDataResources))]
        [Required]
        public string UserName
        {
            get
            {
                return this.userName;
            }

            set
            {
                if (this.userName != value)
                {
                    this.ValidateProperty("UserName", value);
                    this.userName = value;
                    this.RaisePropertyChanged("UserName");
                }
            }
        }

        /// <summary>
        /// Gets or sets a function that returns the password.
        /// </summary>
        internal Func<string> PasswordAccessor { get; set; }

        /// <summary>
        /// Gets and sets the password.
        /// </summary>
        [Display(Name = "PasswordLabel", ResourceType = typeof(RegistrationDataResources))]
        [Required]
        public string Password
        {
            get
            {
                return (this.PasswordAccessor == null) ? string.Empty : this.PasswordAccessor();
            }
            set
            {
                this.ValidateProperty("Password", value);

                // Do not store the password in a private field as it should not be stored in memory in plain-text.
                // Instead, the supplied PasswordAccessor serves as the backing store for the value.

                this.RaisePropertyChanged("Password");
            }
        }

        /// <summary>
        /// Gets and sets the value indicating whether the user's authentication information should be recorded for future logins.
        /// </summary>
        [Display(Name = "RememberMeLabel", ResourceType = typeof(ApplicationStrings))]
        public bool RememberMe
        {
            get
            {
                return this.rememberMe;
            }

            set
            {
                if (this.rememberMe != value)
                {
                    this.ValidateProperty("RememberMe", value);
                    this.rememberMe = value;
                    this.RaisePropertyChanged("RememberMe");
                }
            }
        }

        /// <summary>
        /// Gets or sets the current login operation.
        /// </summary>
        internal LoginOperation CurrentLoginOperation
        {
            get
            {
                return this.currentLoginOperation;
            }
            set
            {
                if (this.currentLoginOperation != value)
                {
                    if (this.currentLoginOperation != null)
                    {
                        this.currentLoginOperation.Completed -= (s, e) => this.CurrentLoginOperationChanged();
                    }

                    this.currentLoginOperation = value;

                    if (this.currentLoginOperation != null)
                    {
                        this.currentLoginOperation.Completed += (s, e) => this.CurrentLoginOperationChanged();
                    }

                    this.CurrentLoginOperationChanged();
                }
            }
        }

        /// <summary>
        /// Gets a value indicating whether the user is presently being logged in.
        /// </summary>
        [Display(AutoGenerateField = false)]
        public bool IsLoggingIn
        {
            get
            {
                return this.CurrentLoginOperation != null && !this.CurrentLoginOperation.IsComplete;
            }
        }

        /// <summary>
        /// Gets a value indicating whether the user can presently log in.
        /// </summary>
        [Display(AutoGenerateField = false)]
        public bool CanLogIn
        {
            get
            {
                return !this.IsLoggingIn;
            }
        }

        /// <summary>
        /// Raises operation-related property change notifications when the current login operation changes.
        /// </summary>
        private void CurrentLoginOperationChanged()
        {
            this.RaisePropertyChanged("IsLoggingIn");
            this.RaisePropertyChanged("CanLogIn");
        }

        /// <summary>
        /// Creates a new <see cref="LoginParameters"/> instance using the data stored in this entity.
        /// </summary>
        public LoginParameters ToLoginParameters()
        {
            return new LoginParameters(this.UserName, this.Password, this.RememberMe, null);
        }
    }
}