using a Code Snippet for INotifyPropertyChanged

Question

I found this code snippet for INotifyPropertyChanged

But it shows the code like this :

Answer 1

I'm going to give you the answer you don't want to hear: You shouldn't need to do this at all. Your model should have the (full or auto) properties, and then your ViewModel properties should just have a getter and a setter that returns _model.MyProperty.

Also, you may want to look into CallerMemberName to get rid of that pesky magic string. I'll post some examples if you want me to.

---

For example, I have a DealsUser model class (note how internal logic like generating the email address if it was never explicitly set, is done here):

public class DealsUser : IDealsUser
{
    public DealsUser() : this("GUEST")
    {
    }

    public DealsUser(string username)
    {
        this.Username = username;
        this.IsAdministrator = false;
        this.IsPlanModerator = false;
        this.IsPlanner = false;
    }

    public string Username { get; set; }

    public bool IsAdministrator { get; set; }

    public bool IsPlanModerator { get; set; }

    public bool IsPlanner { get; set; }

    private string _emailAddress;
    public string EmailAddress
    {
        get
        {
            return _emailAddress ?? string.Format(
                "{0}@mycompany.co.za", this.Username);
        }
        set
        {
            _emailAddress = value;
        }
    }

    public override string ToString()
    {
        return this.Username;
    }

And I have a BaseViewModel class with the following event and protected methods (note how we use CallerMemberName to eliminate magic strings):

#region INotifyPropertyChanged Members

public event PropertyChangedEventHandler PropertyChanged;

protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
{
    var eventHandler = this.PropertyChanged;
    if (eventHandler != null)
    {
        eventHandler(this, new PropertyChangedEventArgs(propertyName));
    }
}

protected bool SetProperty(ref T storage, T value,
    [CallerMemberName] string propertyName = null)
{
    if (object.Equals(storage, value))
    {
        return false;
    }

    storage = value;
    this.OnPropertyChanged(propertyName);
    return true;
}

protected bool SetModelProperty(T storage, T value, Action setter,
    [CallerMemberName] string propertyName = null)
{
    if (object.Equals(storage, value))
    {
        return false;
    }

    setter();
    this.OnPropertyChanged(propertyName);
    return true;
}

#endregion

I then inherit from BaseViewModel, I dependency inject the model into my constructor, and I try to keep my ViewModel as lean as possible. Note that I have to use SetModelProperty instead of SetProperty, because you cannot pass a property (e.g. _dealsUser.Username) into a lamba function as a reference variable. Also note that IsPlanner and IsPlanModerator contain extra logic that updates related notifying properties when they change:

public class DealsUserVM : BaseViewModel
{
    private readonly IDealsUser _dealsUser;

    public DealsUserVM()
        : this(new DealsUser())
    {
        // Empty ctor
    }

    public DealsUserVM(IDealsUser dealsUser)
    {
        _dealsUser = dealsUser;
    }

    public IDealsUser Model
    {
        get
        {
            return _dealsUser;
        }
    }

    public string Username
    {
        get { return _dealsUser.Username; }
        set
        {
            SetModelProperty(_dealsUser.Username, value,
                () => { _dealsUser.Username = value; });
        }
    }

    public bool IsAdministrator
    {
        get { return _dealsUser.IsAdministrator; }
        set
        {
            SetModelProperty(_dealsUser.IsAdministrator, value,
                () => { _dealsUser.IsAdministrator = value; });
        }
    }

    public bool IsPlanModerator
    {
        get { return _dealsUser.IsPlanModerator; }
        set
        {
            // If IsPlanModerator has changed (and was updated as a result)
            if (SetModelProperty(_dealsUser.IsPlanModerator, value,
                () => { _dealsUser.IsPlanModerator = value; }))
            {
                // If IsPlanModerator is now TRUE
                if (value)
                {
                    this.IsPlanner = true;
                }
            }
        }
    }

    public bool IsPlanner
    {
        get { return _dealsUser.IsPlanner; }
        set
        {
            // If IsPlanner has changed (and was updated as a result)
            if (SetModelProperty(_dealsUser.IsPlanner, value,
                    () => { _dealsUser.IsPlanner = value; }))
            {
                // If IsPlanner is now FALSE
                if (!value)
                {
                    this.IsPlanModerator = false;
                }
            }
        }
    }

    public string EmailAddress
    {
        get { return _dealsUser.EmailAddress; }
        set
        {
            SetModelProperty(_dealsUser.EmailAddress, value,
                () => { _dealsUser.EmailAddress = value; });
        }
    }

    public override string ToString()
    {
        return _dealsUser.ToString();
    }
}

Hope this helps :-)