ObservableCollection and DisplayMemberBinding - wpf

Question

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; }
public double ValueX { get; set; }
public int ValueY { get; 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;
}
public double ValueX {
get {
return _value.ValueX;
}
set {
if(Math.Abs(_value.ValueX - value) < Mathematics.EPSILON) return;
_value.ValueX = value;
OnPropertyChanged("ValueX");
}
}
public int ValueY {
get { return _value.ValueY; }
set {
if(_value.ValueX == value) return;
_value.ValueY = value;
OnPropertyChanged("ValueY");
}
}
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?

Answer 1

Since you bind ItemsSource to ObservableCollection<Point> it means that each item is of a Point type which has ValueX and ValueY declared as fields which are not valid binding source. Change them to properties:
public double ValueX { get; private set; }
public double ValueY { get; private set; }
Besides you use Mode=TwoWay for something that is read only. This should be changed to OneWay. If you want to leave TwoWay binding then remove private from the setter but then also you'll need to change GridViewColumn.CellTemplate to be some TextBox instead of using DisplayMemberBinding which is for display only.