Question

I’m trying to bind some XAML code to a property in my ViewModel.

<Grid Visibility="{Binding HasMovies, Converter={StaticResources VisibilityConverter}}">
...
</Grid>

My ViewModel is setup like this:

private bool _hasMovies;
        public bool HasMovies
        {
            get { return _hasMovies; }
            set { _hasMovies = value; RaisePropertyChanged("HasMovies"); }
        }

In the constructor of the ViewModel, I set the HasMovies link:

MovieListViewModel()
{
   HasMovies = CP.Connection.HasMovies;
}

in CP:

public bool HasMovies
        {
            get { return MovieList != null && MovieList.Count > 0; }
        }

private ObservableCollection<Movie> _movies;
        public ObservableCollection<Movie> MovieList
        {
            get { return _movies; }
            set
            {
                _movies = value;
                RaisePropertyChanged("MovieList");
                RaisePropertyChanged("HasMovies");
                _movies.CollectionChanged += MovieListChanged;
            }
        }

        private void MovieListChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            RaisePropertyChanged("HasMovies");
        }

What am I doing wrong? How should I change this binding so that it reflects the current state of CP.Connection.HasMovies?

Answer 1

Either directly expose the object in the ViewModel and bind directly through that (so that the value is not just copied once which is what happens now) or subscribe to the PropertyChanged event and set HasMovies to the new value every time it changes in your source object.

e.g.

CP.Connection.PropertyChanged += (s,e) =>
    {
        if (e.PropertyName = "HasMovies") this.HasMovies = CP.Connection.HasMovies;
    };