Question

I have a listbox defined in XAML as:

<ListBox x:Name="directoryList"
                 MinHeight="100" 
                 Grid.Row="0"
                 ItemsSource="{Binding Path=SelectedDirectories}"/>

The SelectedDirectories is a property on the lists DataContext of type List<DirectoryInfo>

The class which is the datacontext for the listbox implements INotifyPropertyChanged. When the collection changes the items are added successfully to the list however the display does not update until I force the listbox to redraw by resizing it.

Any ideas why?

EDIT: INotifyPropertyChanged implementation

public class FileScannerPresenter : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        private FileScanner _FileScanner;

        public FileScannerPresenter()
        {
            this._FileScanner = new FileScanner();
        }

        public List<DirectoryInfo> SelectedDirectories
        {
            get
            {
                return _FileScanner.Directories;
            }
        }

        public void AddDirectory(string path)
        {
            this._FileScanner.AddDirectory(path);
            OnPropertyChanged("SelectedDirectories");
        }

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

Answer 1

Try

ObservableCollection<DirectoryInfo> 

instead – you’re triggering a refresh of the entire ListBox for no reason, and you don’t need to make your hosting class implement INotifyPropertyChanged – it could easily just be a property of the window. The key is to never set the property to a new instance. So:

class SomeWindow : Window {
    public ObservableCollection<DirectoryInfo> SelectedDirectories {get; private set;}

    SomeWindow() { SelectedDirectories = new ObservableCollection<DirectoryInfo>(); }

    public void AddDirectory(string path) {
        SelectedDirectories.Add(new DirectoryInfo(path));
    }
}

If you end up using that FileScanner class, you need to implement INotifyCollectionChanged instead – that way, the ListBox knows what to add/remove dynamically.