Scrollable Charts

View model

using System;
using System.Linq;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using LiveChartsCore;
using LiveChartsCore.Defaults;
using LiveChartsCore.Kernel.Events;
using LiveChartsCore.Kernel.Sketches;

namespace ViewModelsSamples.General.Scrollable;

public partial class ViewModel : ObservableObject
{
    private static double _defaultMin = 0;
    private static double _defaultMax = 100;
    private bool _isDown = false;

    public ObservablePoint[] Values { get; } = Fetch();

    [ObservableProperty]
    public partial double MinX { get; set; }

    [ObservableProperty]
    public partial double MaxX { get; set; }

    [ObservableProperty]
    public partial double MinXThumb { get; set; } = _defaultMin;

    [ObservableProperty]
    public partial double MaxXThumb { get; set; } = _defaultMax;

    [RelayCommand]
    public void ChartUpdated(ChartCommandArgs args)
    {
        var cartesianChart = (CartesianChartEngine)args.Chart.CoreChart;
        var x = cartesianChart.XAxes.First();

        // when the main chart is updated, we need to update the scroll bar thumb limits
        // this will sync the scroll bar with the main chart when the user is zooming or panning

        MinXThumb = x.MinLimit ?? _defaultMin;
        MaxXThumb = x.MaxLimit ?? _defaultMax;
    }

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

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

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

        var currentRange = MaxXThumb - MinXThumb;

        var min = positionInData.X - currentRange / 2;
        var max = positionInData.X + currentRange / 2;

        // optional, use the data bounds as limits for the thumb
        if (min < Values[0].X)
        {
            min = Values[0].X ?? _defaultMin;
            max = min + currentRange;
        }
        if (max > Values[^1].X)
        {
            max = Values[^1].X ?? _defaultMax;
            min = max - currentRange;
        }

        // update the scroll bar thumb when the user is dragging the chart
        MinXThumb = min;
        MaxXThumb = max;

        // update the chart visible range
        MinX = min;
        MaxX = max;
    }

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

    private static ObservablePoint[] Fetch()
    {
        var trend = 1000;
        var r = new Random();

        var values = new ObservablePoint[500];

        for (var i = 0; i < 500; i++)
            values[i] = new ObservablePoint(i, trend += r.Next(-20, 20));

        return values;
    }
}

XAML

<UserControl
    x:Class="AvaloniaSample.General.Scrollable.View"
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:lvc="using:LiveChartsCore.SkiaSharpView.Avalonia"
    xmlns:vms="using:ViewModelsSamples.General.Scrollable"
    x:DataType="vms:ViewModel">

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

    <Grid RowDefinitions="*, 100">

        <!--
        We use the DrawMargin property to align both charts,
        both charts have a left margin of 100 and a right margin of 50
        -->

        <lvc:CartesianChart
            Grid.Row="0"
            DrawMargin="{lvc:Margin '100, Auto, 50, Auto'}"
            ZoomMode="X"
            UpdateStartedCommand="{Binding ChartUpdatedCommand}">

            <lvc:CartesianChart.Series>
                <lvc:XamlLineSeries
                    Values="{Binding Values}"
                    GeometryStroke="{x:Null}"
                    GeometryFill="{x:Null}"
                    DataPadding="{lvc:Point '0,1'}"/>
            </lvc:CartesianChart.Series>

            <lvc:CartesianChart.XAxes>
                <lvc:XamlAxis
                    MinLimit="{Binding MinX}"
                    MaxLimit="{Binding MaxX}"/>
            </lvc:CartesianChart.XAxes>

        </lvc:CartesianChart>

        <lvc:CartesianChart
            Grid.Row="1"
            DrawMargin="{lvc:Margin '100, Auto, 50, Auto'}"
            PointerPressedCommand="{Binding PointerDownCommand}"
            PointerMoveCommand="{Binding PointerMoveCommand}"
            PointerReleasedCommand="{Binding PointerUpCommand}"
            TooltipPosition="Hidden">

            <lvc:CartesianChart.Series>
                <lvc:XamlLineSeries
                    Values="{Binding Values}"
                    GeometryStroke="{x:Null}"
                    GeometryFill="{x:Null}"
                    DataPadding="{lvc:Point '0,1'}"/>
            </lvc:CartesianChart.Series>

            <lvc:CartesianChart.XAxes>
                <lvc:XamlAxis IsVisible="False"/>
            </lvc:CartesianChart.XAxes>

            <lvc:CartesianChart.YAxes>
                <lvc:XamlAxis IsVisible="False"/>
            </lvc:CartesianChart.YAxes>

            <lvc:CartesianChart.Sections>
                <lvc:XamlRectangularSection
                    Xi="{Binding MinXThumb}"
                    Xj="{Binding MaxXThumb}"
                    Fill="{lvc:SolidColorPaint Color='#64FFCDD2'}"/>
            </lvc:CartesianChart.Sections>
        </lvc:CartesianChart>
    </Grid>

</UserControl>

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