[WPF] Update button availability

Hi, my view-model implements INotifyDataErrorInfo. My goal is to enable save button only when there are no errors:

public bool CanSave()
        {
            return HasErrors == false;
        }

        public async Task Save()
        {
            //bunch of code...
        }

INotifyDataErrorInfo implementation…

public event EventHandler<DataErrorsChangedEventArgs> ErrorsChanged;

        private void Validate(object value, [CallerMemberName]string propertyName = null)
        {
            var results = new Collection<ValidationResult>();
            var context = new ValidationContext(this) { MemberName = propertyName };
            var isValid = Validator.TryValidateProperty(value, context, results);
            if (isValid)
            {
                if (errors.ContainsKey(propertyName))
                    errors.Remove(propertyName);
                RaiseErrorsChanged(propertyName);
            }
            else
            {
                var grouping = from result in results
                               from property in result.MemberNames
                               group result by property into g
                               select g;

                foreach (var group in grouping)
                {
                    var messages = group.Select(r => r.ErrorMessage).ToList();

                    if (errors.ContainsKey(group.Key))
                        errors[group.Key] = messages;
                    else
                        errors.Add(group.Key, messages);
                    RaiseErrorsChanged(group.Key);
                }
            }
        }

        public IEnumerable GetErrors(string propertyName)
        {
            if (!errors.ContainsKey(propertyName))
                return null;
            return errors[propertyName];
        }

        public bool HasErrors
        {
            get { return errors.Any(); }
        }

        public void RaiseErrorsChanged(string propertyName)
        {
            if (ErrorsChanged != null)
                ErrorsChanged(this, new DataErrorsChangedEventArgs(propertyName));
        }

Using Validate method

 private string lastName;
        [Required]
        [Display(Name = "Sobrenome")]
        public string LastName
        {
            get { return this.lastName; }

            set
            {
                Validate(value);
                this.lastName = value;
                this.NotifyOfPropertyChange();
            }
        }

However, the button is always enabled, even if there are errors. I guess the problem is that I need to update button availability whenever an error is raised, but how can I accomplish that?

[nigel-sampson]

Pretty much everything @mvermef said is correct here.

There’s a little guidance I use when deciding if the Guard should be a method or a property. If your actual method is taking parameters such as Login(string username, string password) then CanLogin(string username, string password) makes sense.

However if the Can* method depends on any other property than the parameters then it should be a property where you can trigger property changed notifications when that property changes.

[mvermef]

excellent!