dynamic create Series ,difficult to create TrackBallInfoTemplate

[Si]

                    Chart.Series.Add(new LineSeries
                    {
                        CategoryBinding = binding,
                        ValueBinding = ...,
                        StrokeThickness = 1,
                        Stroke = ...,
                        ItemsSource = vm.Datas,
                        TrackBallInfoTemplate = // difficult to create
                    }); 

 

TrackBallInfoTemplate is difficult to create, how can i only set a stringformat to use trackballinfo