ObservableCollection and DisplayMemberBinding

ObservableCollection and DisplayMemberBinding

I'm trying to fill ListBox by ObservableCollection. But when i add new
item nothing displayed, only empty item adding. There are fragments of my
code: XAML
<ListView ItemsSource="{Binding Points}" SelectedItem="{Binding Point}">
<ListView.View>
<GridView AllowsColumnReorder="False">
<GridViewColumn Header ="X" Width="100" DisplayMemberBinding = "{Binding
Path=ValueX, Mode=TwoWay}" />
<GridViewColumn Header ="Y" Width="100" DisplayMemberBinding = "{Binding
Path=ValueY, Mode=TwoWay}"/>
</GridView>
</ListView.View>
</ListView>
Window class
var value = new Value();
var viewModel = new ViewModel(value);
DataContext = viewModel;
InitializeComponent();
Value class
private const Point POINT = null;
private readonly ObservableCollection<Point> _points = new
ObservableCollection<Point>();
public Value() {
Point = POINT;
Points = _points;
}
public Point Point { get; set; }
public ObservableCollection<Point> Points { get; private set; }
ViewModel class
private readonly Value _value;
public ViewModel(Value value) {
_value = value;
}
public Point Point {
get { return _value.Point; }
set {
_value.Point = value;
OnPropertyChanged("Point");
}
}
public ObservableCollection<Point> Points {
get { return _value.Points; }
}
private RelayCommand _addCommand;
public ICommand AddCommand {
get {
if (_addCommand == null) {
_addCommand = new RelayCommand(Add);
}
return _addCommand;
}
}
private void Add(object obj) {
Points.Add(new Point(ValueX, ValueY));
ValueX = 0;
ValueY = 0;
}
and Point class
public class Point {
public readonly double ValueX;
public readonly double ValueY;
public Point(double valueX, double valueY) {
ValueX = valueX;
ValueY = valueY;
}
public override string ToString() {
return (ValueX + " " + ValueY);
}
}
When i try to add new item, new item is added but nothing is displayed.
What reason can be here?