I was writing a helper class today for WPF and had a IsDirty flag which was firing a PropertyChanged event. However, when I used this in my UI the element that was bound to this flag was not updating.

After a quick look through my code I noticed the following…

private void OnPropertyChanged(string property)
{
    if (null != PropertyChanged)
        PropertyChanged(null, new PropertyChangedEventArgs(property));
}

I’d mistakenly used null as the first parameter to the PropertyChanged handler. After changing the parameter to this everything started working as expected.

So the moral of the story is – WPF needs both the object raising the notification and the property changed events in order to work its magic.