Customize default legends

You can quickly change the position, the font, the text size or the background color:

<UserControl x:Class="UnoWinUISample.Axes.Multiple.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.Axes.Multiple"
            mc:Ignorable="d">
    <UserControl.DataContext>
        <vms:ViewModel/>
    </UserControl.DataContext>
    <lvc:CartesianChart
            Series="{Binding Series}"
            YAxes="{Binding YAxes}"
            LegendPosition="Left"
            LegendTextPaint="{Binding LegendTextPaint}"
            LegendBackgroundPaint="{Binding LedgendBackgroundPaint}"
            LegendTextSize="16">
    </lvc:CartesianChart>
</UserControl>

View model

[ObservableObject]
public partial class ViewModel
{
    public ISeries[] Series { get; set; } = { ... };
    public Axis[] YAxes { get; set; } = { ... };

    public SolidColorPaint LegendTextPaint { get; set; } = // mark
        new SolidColorPaint // mark
        { // mark
            Color = new SKColor(50, 50, 50), // mark
            SKTypeface = SKTypeface.FromFamilyName("Courier New") // mark
        }; // mark

    public SolidColorPaint LegendBackgroundPaint { get; set; } = // mark
        new SolidColorPaint(new SKColor(240, 240, 240)); // mark
}

Legend control from scratch

You can also create your own legend, the recommended way is to use the LiveCharts API (example bellow) but you can use anything as legend as soon as it implements the IChartLegend<T> interface. At the following example we build a custom control to render legends in our charts using the LiveCharts API.

CustomLegend.cs

using System.Linq;
using LiveChartsCore;
using LiveChartsCore.Drawing;
using LiveChartsCore.Kernel.Events;
using LiveChartsCore.Kernel.Sketches;
using LiveChartsCore.Measure;
using LiveChartsCore.SkiaSharpView;
using LiveChartsCore.SkiaSharpView.Drawing;
using LiveChartsCore.SkiaSharpView.Drawing.Geometries;
using LiveChartsCore.SkiaSharpView.Painting;
using LiveChartsCore.SkiaSharpView.VisualElements;
using LiveChartsCore.VisualElements;
using SkiaSharp;

namespace ViewModelsSamples.General.TemplatedLegends;

public class CustomLegend : IChartLegend<SkiaSharpDrawingContext>
{
    private static readonly int s_zIndex = 10050;
    private readonly StackPanel<RoundedRectangleGeometry, SkiaSharpDrawingContext> _stackPanel = new();
    private readonly SolidColorPaint _fontPaint = new(new SKColor(30, 20, 30))
    {
        SKTypeface = SKTypeface.FromFamilyName("Arial", SKFontStyle.Bold),
        ZIndex = s_zIndex + 1
    };

    public void Draw(Chart<SkiaSharpDrawingContext> chart)
    {
        var legendPosition = chart.GetLegendPosition();

        _stackPanel.X = legendPosition.X;
        _stackPanel.Y = legendPosition.Y;

        chart.AddVisual(_stackPanel);
        if (chart.LegendPosition == LegendPosition.Hidden) chart.RemoveVisual(_stackPanel);
    }

    public LvcSize Measure(Chart<SkiaSharpDrawingContext> chart)
    {
        _stackPanel.Orientation = ContainerOrientation.Vertical;
        _stackPanel.MaxWidth = double.MaxValue;
        _stackPanel.MaxHeight = chart.ControlSize.Height;

        // clear the previous elements.
        foreach (var visual in _stackPanel.Children.ToArray())
        {
            _ = _stackPanel.Children.Remove(visual);
            chart.RemoveVisual(visual);
        }

        var theme = LiveCharts.DefaultSettings.GetTheme<SkiaSharpDrawingContext>();

        foreach (var series in chart.Series.Where(x => x.IsVisibleAtLegend))
        {
            var panel = new StackPanel<RectangleGeometry, SkiaSharpDrawingContext>
            {
                Padding = new Padding(12, 6),
                VerticalAlignment = Align.Middle,
                HorizontalAlignment = Align.Middle,
                Children =
                {
                    new SVGVisual
                    {
                        Path = SKPath.ParseSvgPathData(SVGPoints.Star),
                        Width = 25,
                        Height = 25,
                        ClippingMode = ClipMode.None, // required on legends // mark
                        Fill = new SolidColorPaint(theme.GetSeriesColor(series).AsSKColor())
                        {
                            ZIndex = s_zIndex + 1
                        }
                    },
                    new LabelVisual
                    {
                        Text = series.Name ?? string.Empty,
                        Paint = _fontPaint,
                        TextSize = 15,
                        ClippingMode = ClipMode.None, // required on legends // mark
                        Padding = new Padding(8, 0, 0, 0),
                        VerticalAlignment = Align.Start,
                        HorizontalAlignment = Align.Start
                    }
                }
            };

            panel.PointerDown += GetPointerDownHandler(series);
            _stackPanel.Children.Add(panel);
        }

        return _stackPanel.Measure(chart);
    }

    private static VisualElementHandler<SkiaSharpDrawingContext> GetPointerDownHandler(
        IChartSeries<SkiaSharpDrawingContext> series)
    {
        return (visual, args) =>
        {
            series.IsVisible = !series.IsVisible;
        };
    }
}

View

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

    <UserControl.DataContext>
        <vms:ViewModel/>
    </UserControl.DataContext>
    <Grid>
        <lvc:CartesianChart Series="{Binding Series}" LegendPosition="Right" >
            <!-- mark -untilCloses CartesianChart.Legend -->
            <lvc:CartesianChart.Legend>
                <vms:CustomLegend></vms:CustomLegend>
            </lvc:CartesianChart.Legend>
        </lvc:CartesianChart>
    </Grid>

</UserControl>