Scrollable Charts

View model

using System;
using System.Collections.ObjectModel;
using System.Linq;
using CommunityToolkit.Mvvm.Input;
using LiveChartsCore;
using LiveChartsCore.Defaults;
using LiveChartsCore.Kernel.Events;
using LiveChartsCore.Kernel.Sketches;
using LiveChartsCore.SkiaSharpView;
using LiveChartsCore.SkiaSharpView.Drawing;
using LiveChartsCore.SkiaSharpView.Painting;
using SkiaSharp;

namespace ViewModelsSamples.General.Scrollable;

public partial class ViewModel
{
    private bool _isDown = false;
    private readonly ObservableCollection<ObservablePoint> _values = new();

    public ViewModel()
    {
        var trend = 1000;
        var r = new Random();

        for (var i = 0; i < 500; i++)
        {
            _values.Add(new ObservablePoint(i, trend += r.Next(-20, 20)));
        }

        Series = new ISeries[]
        {
            new LineSeries<ObservablePoint>
            {
                Values = _values,
                GeometryStroke = null,
                GeometryFill = null,
                DataPadding = new(0, 1)
            }
        };

        ScrollbarSeries = new ISeries[]
        {
            new LineSeries<ObservablePoint>
            {
                Values = _values,
                GeometryStroke = null,
                GeometryFill = null,
                DataPadding = new(0, 1)
            }
        };

        ScrollableAxes = new[] { new Axis() };

        Thumbs = new[]
        {
            new RectangularSection
            {
                Fill = new SolidColorPaint(new SKColor(255, 205, 210, 100))
            }
        };

        InvisibleX = new[] { new Axis { IsVisible = false } };
        InvisibleY = new[] { new Axis { IsVisible = false } };

        // force the left margin to be 100 and the right margin 50 in both charts, this will
        // align the start and end point of the "draw margin",
        // no matter the size of the labels in the Y axis of both chart.
        var auto = LiveChartsCore.Measure.Margin.Auto;
        Margin = new(100, auto, 50, auto);
    }

    public ISeries[] Series { get; set; }
    public Axis[] ScrollableAxes { get; set; }
    public ISeries[] ScrollbarSeries { get; set; }
    public Axis[] InvisibleX { get; set; }
    public Axis[] InvisibleY { get; set; }
    public LiveChartsCore.Measure.Margin Margin { get; set; }
    public RectangularSection[] Thumbs { get; set; }

    [RelayCommand]
    public void ChartUpdated(ChartCommandArgs args)
    {
        var cartesianChart = (ICartesianChartView<SkiaSharpDrawingContext>)args.Chart;

        var x = cartesianChart.XAxes.First();

        // update the scroll bar thumb when the chart is updated (zoom/pan)
        // this will let the user know the current visible range
        var thumb = Thumbs[0];

        thumb.Xi = x.MinLimit;
        thumb.Xj = x.MaxLimit;
    }

    [RelayCommand]
    public void PointerDown(PointerCommandArgs args)
    {
        _isDown = true;
    }

    [RelayCommand]
    public void PointerMove(PointerCommandArgs args)
    {
        if (!_isDown) return;

        var chart = (ICartesianChartView<SkiaSharpDrawingContext>)args.Chart;
        var positionInData = chart.ScalePixelsToData(args.PointerPosition);

        var thumb = Thumbs[0];
        var currentRange = thumb.Xj - thumb.Xi;

        // update the scroll bar thumb when the user is dragging the chart
        thumb.Xi = positionInData.X - currentRange / 2;
        thumb.Xj = positionInData.X + currentRange / 2;

        // update the chart visible range
        ScrollableAxes[0].MinLimit = thumb.Xi;
        ScrollableAxes[0].MaxLimit = thumb.Xj;
    }

    [RelayCommand]
    public void PointerUp(PointerCommandArgs args)
    {
        _isDown = false;
    }
}

XAML

<UserControl
    x:Class="UnoWinUISample.General.Scrollable.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.General.Scrollable"
    mc:Ignorable="d">

    <UserControl.DataContext>
        <vms:ViewModel/>
    </UserControl.DataContext>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="100"/>
        </Grid.RowDefinitions>

        <lvc:CartesianChart
            Grid.Row="0"
            Series="{Binding Series}"
            XAxes="{Binding ScrollableAxes}"
            ZoomMode="X"
            DrawMargin="{Binding Margin}"
            UpdateStartedCommand="{Binding ChartUpdatedCommand}">
        </lvc:CartesianChart>

        <lvc:CartesianChart
            x:Name="ScrollBarChart"
            Grid.Row="1"
            Series="{Binding ScrollbarSeries}"
            DrawMargin="{Binding Margin}"
            Sections="{Binding Thumbs}"
            XAxes="{Binding InvisibleX}"
            YAxes="{Binding InvisibleY}"
            PointerPressedCommand="{Binding PointerDownCommand}"
            PointerMoveCommand="{Binding PointerMoveCommand}"
            PointerReleasedCommand="{Binding PointerUpCommand}"
            TooltipPosition="Hidden">
        </lvc:CartesianChart>
    </Grid>

</UserControl>

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