Customize default legends

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

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="XamarinSample.Axes.Multiple.View"
             xmlns:lvc="clr-namespace:LiveChartsCore.SkiaSharpView.Xamarin.Forms;assembly=LiveChartsCore.SkiaSharpView.XamarinForms"
             xmlns:vms="clr-namespace:ViewModelsSamples.Axes.Multiple;assembly=ViewModelsSamples">
    <ContentPage.BindingContext>
        <vms:ViewModel/>
    </ContentPage.BindingContext>
    <lvc:CartesianChart
            Series="{Binding Series}"
            YAxes="{Binding YAxes}"
            LegendPosition="Bottom"
            LegendBackgroundPaint="{Binding LegendTextPaint}"
            LegendTextPaint="{Binding LegendTextPaint}"
            LegendTextSize="16">
    </lvc:CartesianChart>
</ContentPage>

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

Tooltip 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 tooltip 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.Sketches;
using LiveChartsCore.Measure;
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>, IImageControl
{
    private static readonly int s_zIndex = 10050;
    private StackPanel<RoundedRectangleGeometry, SkiaSharpDrawingContext>? _stackPanel;
    private readonly SolidColorPaint _backgroundPaint = new(new SKColor(28, 49, 58)) { ZIndex = s_zIndex };
    private readonly SolidColorPaint _fontPaint = new(new SKColor(230, 230, 230)) { ZIndex = s_zIndex + 1 };

    public LvcSize Size { get; set; }

    public void Draw(Chart<SkiaSharpDrawingContext> chart)
    {
        if (chart.LegendPosition == LegendPosition.Hidden) return;

        Measure(chart);
        if (_stackPanel is null) return;
        var actualChartSize = chart.ControlSize;

        if (chart.LegendPosition == LegendPosition.Top)
        {
            chart.Canvas.StartPoint = new LvcPoint(0, Size.Height);
            _stackPanel.X = actualChartSize.Width * 0.5f - Size.Width * 0.5f;
            _stackPanel.Y = -Size.Height;
        }
        if (chart.LegendPosition == LegendPosition.Bottom)
        {
            _stackPanel.X = actualChartSize.Width * 0.5f - Size.Width * 0.5f;
            _stackPanel.Y = actualChartSize.Height;
        }
        if (chart.LegendPosition == LegendPosition.Left)
        {
            chart.Canvas.StartPoint = new LvcPoint(Size.Width, 0);
            _stackPanel.X = -Size.Width;
            _stackPanel.Y = actualChartSize.Height * 0.5f - Size.Height * 0.5f;
        }
        if (chart.LegendPosition == LegendPosition.Right)
        {
            _stackPanel.X = actualChartSize.Width;
            _stackPanel.Y = actualChartSize.Height * 0.5f - Size.Height * 0.5f;
        }

        chart.AddVisual(_stackPanel);
    }

    public void Measure(IChart chart)
    {
        var skiaChart = (Chart<SkiaSharpDrawingContext>)chart;
        BuildLayout(skiaChart);
        if (_stackPanel is null) return;
        Size = _stackPanel.Measure(skiaChart, null, null);
    }

    private void BuildLayout(Chart<SkiaSharpDrawingContext> chart)
    {
        _stackPanel ??= new StackPanel<RoundedRectangleGeometry, SkiaSharpDrawingContext>
        {
            Padding = new Padding(15),
            Orientation = ContainerOrientation.Vertical,
            HorizontalAlignment = Align.Start,
            VerticalAlignment = Align.Middle,
            BackgroundPaint = _backgroundPaint
        };

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

        foreach (var series in chart.ChartSeries)
        {
            var sketch = series.GetMiniatresSketch();
            var relativePanel = sketch.AsDrawnControl();

            var label = new LabelVisual
            {
                Text = series.Name ?? string.Empty,
                Paint = _fontPaint,
                TextSize = 15,
                Padding = new Padding(8, 0, 0, 0),
                VerticalAlignment = Align.Start,
                HorizontalAlignment = Align.Start
            };

            var sp = new StackPanel<RoundedRectangleGeometry, SkiaSharpDrawingContext>
            {
                Padding = new Padding(0, 4),
                VerticalAlignment = Align.Middle,
                HorizontalAlignment = Align.Middle,
                Children =
                {
                    relativePanel,
                    label
                }
            };

            _ = _stackPanel?.Children.Add(sp);
        }
    }
}

View

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="XamarinSample.General.TemplatedLegends.View"
             xmlns:lvc="clr-namespace:LiveChartsCore.SkiaSharpView.Xamarin.Forms;assembly=LiveChartsCore.SkiaSharpView.XamarinForms"
             xmlns:vms="clr-namespace:ViewModelsSamples.General.TemplatedLegends;assembly=ViewModelsSamples"
             xmlns:core="clr-namespace:LiveChartsCore;assembly=LiveChartsCore">

    <ContentPage.BindingContext>
        <vms:ViewModel/>
    </ContentPage.BindingContext>

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <lvc:CartesianChart Grid.Row="0" Series="{Binding Series}" LegendPosition="Bottom">
            <!-- mark -untilCloses CartesianChart.Legend -->
            <lvc:CartesianChart.Legend>
                <vms:CustomLegend></vms:CustomLegend>
            </lvc:CartesianChart.Legend>
        </lvc:CartesianChart>
    </Grid>
</ContentPage>