<Polyline Points="{Binding Points}" Stroke="Black"></Polyline>

private PointCollection points = new PointCollection();

  public MyCustomClass()
        {            
            InitializeComponent();
            AddChart();
        }

        public PointCollection Points
        {
            get { return points; }
        }

private void AddChart()
        {
            for (int i = 0; i < 1000; i++)
            {
                double y =  Math.Sin(i);
                Points.Add(new Point(y, i));
            }
            NotifyPropertyChanged("Points"); 
        }