Updating Viewmodel from Event - PropertyChangedEventHandler is null?

Question

I have a property in my WPF app that I am trying to bind to the UI. When I update the property directly inside the viewmodel it works as I expect it to. However, when I try to update this property from inside another class using an Event, the binding doesn't seem to work. Under closer inspection I think this is happening because PropertyChangedEventHandler is null when this happens.

My property inside the ViewModel:

public int BeatNumber
        {
            get
            {
                return beatNumber;
            }
            set
            {
                if (beatNumber != value)
                {
                    this.beatNumber = value;
                    RaisePropertyChanged(() => BeatNumber);
                }
            }
        }

Event inside ViewModel:

public event EventHandler GetHtmlDone = delegate { };


public void GetHTML(string url)
{
    BeatNumber++;
}

Notification Object:

public class NotificationObject : INotifyPropertyChanged
    {
        protected void RaisePropertyChanged<T>(Expression<Func<T>> action)
        {
            var propertyName = GetPropertyName(action);
            RaisePropertyChanged(propertyName);
        }

        private static string GetPropertyName<T>(Expression<Func<T>> action)
        {
            var expression = (MemberExpression)action.Body;
            var propertyName = expression.Member.Name;
            return propertyName;
        }

        private void RaisePropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }



        public event PropertyChangedEventHandler PropertyChanged;
    }

How do I get this binding to update when my event is called from another class?

Answer 1

Solve it by using Commands instead of calling methods from Events.

See ICommand interface for more information