Customize default tooltips

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

View

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage x:Class="MauiSample.Axes.NamedLabels.View"
             xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:lvc="clr-namespace:LiveChartsCore.SkiaSharpView.Maui;assembly=LiveChartsCore.SkiaSharpView.Maui"
             xmlns:vms="clr-namespace:ViewModelsSamples.Axes.NamedLabels;assembly=ViewModelsSamples"
             >
    <ContentPage.BindingContext>
        <vms:ViewModel/>
    </ContentPage.BindingContext>
	<ContentPage.Content>
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="*"/>
            </Grid.RowDefinitions>

            <lvc:CartesianChart
                Series="{Binding Series}"
                XAxes="{Binding XAxes}"
                YAxes="{Binding YAxes}"
                TooltipPosition="Left"
                TooltipBackgroundPaint="{Binding TooltipBackgroundPaint}"
                TooltipTextPaint="{Binding TooltipTextPaint}"
                TooltipTextSize="16">
            </lvc:CartesianChart>

        </Grid>
    </ContentPage.Content>
</ContentPage>

View model

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

    public SolidColorPaint TooltipTextPaint { get; set; } = // mark
        new SolidColorPaint // mark
        { // mark
            Color = new SKColor(242, 244, 195), // mark
            SKTypeface = SKTypeface.FromFamilyName("Courier New") // mark
        }; // mark

    public SolidColorPaint TooltipBackgroundPaint { get; set; } = // mark
        new SolidColorPaint(new SKColor(72, 0, 50)); // mark
}

Customize tooltip format

You can define the text the tooltip will display for a given point, using the YToolTipLabelFormatter, XToolTipLabelFormatter or ToolTipLabelFormatter properties, these properties are of type Func<ChartPoint, string> it means that both are a function, that takes a point as parameter and return a string, the point will be injected by LiveCharts in this function to get a string out of it when it requires to build the text for a point in a tooltip, the injected point will be different as the user moves the pointer over the user interface.

By default the library already defines a default formatter for every series, all the series have a different formatters, but generally the default value uses the Series.Name and the ChartPoint.Coordinate.PrimaryValue properties, the following code snippet illustrates how to build a custom tooltip formatter.

Lets take the example of the next series:"

public ISeries[] Series { get; set; } = [
    new LineSeries<double>
    {
        Values = [2, 1, 3, 5, 3, 4, 6],
        Fill = null,
        GeometrySize = 20,
    },
    new LineSeries<int, StarGeometry>
    {
        Values = [4, 2, 5, 2, 4, 5, 3],
        Fill = null,
        GeometrySize = 20
    }
];

By default the tooltip will be:

We can add format to the tooltip:

public ISeries[] Series { get; set; } = [
    new LineSeries<double>
    {
        Values = [2, 1, 3, 5, 3, 4, 6],
        Fill = null,
        GeometrySize = 20,
        YToolTipLabelFormatter = point => point.Model.ToString("N2") // mark
    },
    new LineSeries<int, StarGeometry>
    {
        Values = [4, 2, 5, 2, 4, 5, 3],
        Fill = null,
        GeometrySize = 20,
        YToolTipLabelFormatter = point => point.Model.ToString("N2") // mark
    }
];

We used the Model property of the point, the Model property is just the item in the Values collection, for example in the next case, the Model property is of type City.

public ISeries[] Series { get; set; } = [
    new LineSeries<City>
    {
        Values = [new() { Population = 4 }, new() { Population = 2}],
        YToolTipLabelFormatter = point => point.Model.Population.ToString("N2") // mark
    }
];

// ...

public class City
{
    public double Population { get; set; }
}

We can also show a label for the X coordinate, the default tooltip uses the X label as the header in the tooltip.

new LineSeries<double>
{
    Values = [2, 1, 3, 5, 3, 4, 6],
    Fill = null,
    GeometrySize = 20,
    XToolTipLabelFormatter = point => point.Index.ToString(), // mark
    YToolTipLabelFormatter = point => point.Model.ToString("C2")
};

When the series is "Stacked" (PieSeries, StackedColumn or StackedRow) we can find information about the stacked data in the StackedValue property, for example:

public ISeries[] Series { get; set; } = [
    new StackedColumnSeries<double>
    {
        Values = [2, 1, 3, 5, 3, 4, 6],
        YToolTipLabelFormatter =
            point => $"{point.Model} / {point.StackedValue!.Total} ({point.StackedValue.Share:P2})"
    },
    new StackedColumnSeries<int>
    {
        Values = [4, 2, 5, 2, 4, 5, 3],
        YToolTipLabelFormatter =
            point => $"{point.Model} / {point.StackedValue!.Total} ({point.StackedValue.Share:P2})"
    }
];

Will result in:

Tooltip control from scratch

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

CustomTooltip.cs

using System;
using System.Collections.Generic;
using LiveChartsCore;
using LiveChartsCore.Drawing;
using LiveChartsCore.Kernel;
using LiveChartsCore.Kernel.Sketches;
using LiveChartsCore.SkiaSharpView.Drawing;
using LiveChartsCore.SkiaSharpView.Drawing.Geometries;
using LiveChartsCore.SkiaSharpView.Drawing.Layouts;
using LiveChartsCore.SkiaSharpView.Painting;
using SkiaSharp;

namespace ViewModelsSamples.General.TemplatedTooltips;

public class CustomTooltip : IChartTooltip
{
    private Container<RoundedRectangleGeometry>? _container;
    private StackLayout? _layout;

    public void Show(IEnumerable<ChartPoint> foundPoints, Chart chart)
    {
        if (_container is null || _layout is null)
        {
            _container = new Container<RoundedRectangleGeometry>
            {
                Content = _layout = new StackLayout
                {
                    Padding = new(10),
                    Orientation = ContainerOrientation.Vertical,
                    HorizontalAlignment = Align.Middle,
                    VerticalAlignment = Align.Middle
                }
            };

            _container.Geometry.Fill = new SolidColorPaint(new SKColor(28, 49, 58));
            _container.Animate(new Animation(EasingFunctions.BounceOut, TimeSpan.FromMilliseconds(500)));

            var drawTask = chart.Canvas.AddGeometry(_container);
            drawTask.ZIndex = 10100;
        }

        _container.Opacity = 1;
        _container.ScaleTransform = new LvcPoint(1, 1);

        foreach (var child in _layout.Children.ToArray())
            _ = _layout.Children.Remove(child);

        foreach (var point in foundPoints)
        {
            var series = point.Context.Series;
            var miniature = (IDrawnElement<SkiaSharpDrawingContext>)series.GetMiniatureGeometry(point);

            var label = new LabelGeometry
            {
                Text = point.Coordinate.PrimaryValue.ToString("C2"),
                Paint = new SolidColorPaint(new SKColor(230, 230, 230)),
                TextSize = 15,
                Padding = new Padding(8, 0, 0, 0),
                VerticalAlign = Align.Start,
                HorizontalAlign = Align.Start
            };

            var sp = new StackLayout
            {
                Padding = new Padding(0, 4),
                VerticalAlignment = Align.Middle,
                HorizontalAlignment = Align.Middle,
                Children =
                {
                    miniature,
                    label
                }
            };

            _layout.Children.Add(sp);
        }

        var size = _container.Measure();
        var location = foundPoints.GetTooltipLocation(size, chart);

        _container.X = location.X;
        _container.Y = location.Y;

        chart.Canvas.Invalidate();
    }

    public void Hide(Chart chart)
    {
        if (chart is null || _container is null) return;

        _container.Opacity = 0f;
        _container.ScaleTransform = new LvcPoint(0f, 0f);

        chart.Canvas.Invalidate();
    }
}

View

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage x:Class="MauiSample.General.TemplatedTooltips.View"
             xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:lvc="clr-namespace:LiveChartsCore.SkiaSharpView.Maui;assembly=LiveChartsCore.SkiaSharpView.Maui"
             xmlns:vms="clr-namespace:ViewModelsSamples.General.TemplatedTooltips;assembly=ViewModelsSamples"
             >

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

    <ContentPage.Content>
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="*"/>
            </Grid.RowDefinitions>
            
            <lvc:CartesianChart
                Grid.Row="0"
                Series="{Binding Series}">
                <!-- mark -untilCloses CartesianChart.Tooltip -->
                <lvc:CartesianChart.Tooltip>
                    <vms:CustomTooltip></vms:CustomTooltip>
                </lvc:CartesianChart.Tooltip>
            </lvc:CartesianChart>
        </Grid>
    </ContentPage.Content>
</ContentPage>

Override Series.FindPointsInPosition

Depending on the series type and FindingStrategy, LiveCharts decides the logic to show points on tooltips and also the points passed to any pointer event in the library (like Hover, HoverLeft or PointerDown), lets take as an example the default behavior of the ColumnSeries<T>, it selects all the points that share the same X coordinate:

But for this example, we want to override this behavior, instead we only need the tooltip to display the exact column where the pointer is in:

When the FindingStrategy, is not enough, we can override the logic to determine whether a given point is inside a drawn ChartPoint. This method will be used by the library to resolve the points to show in a tooltip, or the points passed in any pointer event:

using System.Collections.Generic;
using System.Linq;
using LiveChartsCore;
using LiveChartsCore.Drawing;
using LiveChartsCore.Kernel;
using LiveChartsCore.Kernel.Drawing;
using LiveChartsCore.Measure;
using LiveChartsCore.SkiaSharpView;

namespace ViewModelsSamples.Events.OverrideFind;

public class ViewModel
{
    public ISeries[] Series { get; set; } = [
        new CustomColumnSeries<int> { Values = [9, 5, 7, 3, 7, 3] },
        new CustomColumnSeries<int> { Values = [8, 2, 3, 2, 5, 2] }
    ];

    public class CustomColumnSeries<T> : ColumnSeries<T>
    {
        protected override IEnumerable<ChartPoint> FindPointsInPosition(
            Chart chart, LvcPoint pointerPosition, FindingStrategy strategy, FindPointFor findPointFor)
        {
            return Fetch(chart).Where(point =>
            {
                var ha = (RectangleHoverArea?)point.Context.HoverArea;
                if (ha is null) return false;

                var isInsideX = ha.X <= pointerPosition.X && pointerPosition.X <= ha.X + ha.Width;
                var isInsideY = ha.Y <= pointerPosition.Y && pointerPosition.Y <= ha.Y + ha.Height;

                return findPointFor == FindPointFor.HoverEvent
                    ? isInsideX
                    : isInsideY;
            });
        }
    }
}