Add Point On Click

View model

using System.Collections.ObjectModel;
using CommunityToolkit.Mvvm.ComponentModel;
using LiveChartsCore;
using LiveChartsCore.Defaults;
using LiveChartsCore.SkiaSharpView;

namespace ViewModelsSamples.Events.AddPointOnClick;

public partial class ViewModel : ObservableObject
{
    public ViewModel()
    {
        var data = new ObservableCollection<ObservablePoint>
        {
            new(0, 5),
            new(3, 8),
            new(7, 9)
        };

        Data = data;

        SeriesCollection = new ISeries[]
        {
            new LineSeries<ObservablePoint>
            {
                Values = data,
                Fill = null,
                DataPadding = new LiveChartsCore.Drawing.LvcPoint(5, 5)
            }
        };
    }

    public ObservableCollection<ObservablePoint> Data { get; set; }

    public ISeries[] SeriesCollection { get; set; }
}

XAML

<UserControl
    x:Class="UnoWinUISample.Events.AddPointOnClick.View"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:lvc="using:LiveChartsCore.SkiaSharpView.WinUI"
    xmlns:vms="using:ViewModelsSamples.Events.AddPointOnClick"
    mc:Ignorable="d">

    <UserControl.DataContext>
        <vms:ViewModel/>
    </UserControl.DataContext>
    <lvc:CartesianChart
        x:Name="chart"
        Series="{Binding SeriesCollection}"
        PointerPressed="Chart_PointerPressed"
        TooltipPosition="Hidden">
    </lvc:CartesianChart>
</UserControl>

View code behind

using LiveChartsCore.Defaults;
using LiveChartsCore.Drawing;
using ViewModelsSamples.Events.AddPointOnClick;
using Microsoft.UI.Xaml.Controls;

namespace UnoWinUISample.Events.AddPointOnClick;

public sealed partial class View : UserControl
{
    public View()
    {
        InitializeComponent();
    }

    private void Chart_PointerPressed(object sender, Microsoft.UI.Xaml.Input.PointerRoutedEventArgs e)
    {
        var viewModel = (ViewModel)DataContext;

        // gets the point in the UI coordinates.
        var p = e.GetCurrentPoint(chart);

        // scales the UI coordinates to the corresponding data in the chart.
        var dataCoordinates = chart.ScalePixelsToData(new LvcPointD(p.Position.X, p.Position.Y));

        // finally add the new point to the data in our chart.
        viewModel?.Data.Add(new ObservablePoint(dataCoordinates.X, dataCoordinates.Y));

        // You can also get all the points or visual elements in a given location.
        var points = chart.GetPointsAt(new LvcPoint((float)p.Position.X, (float)p.Position.Y));
        var visuals = chart.GetVisualsAt(new LvcPoint((float)p.Position.X, (float)p.Position.Y));
    }
}