Trackball

Trackball feature displays the tooltip for the data points that are closer to the point where you touch on the chart area. This feature, especially, can be used instead of data label feature when you cannot show data labels for all data points due to space constraint. To enable this feature, add an instance of ChartTrackballBehavior to the ChartBehaviors collection property of SfChart. Trackball will be activated once you long-press anywhere on the chart area. Once it is activated, it will appear in the UI and move based on your touch movement until you stop touching on the chart.

You can use the following properties to show/hide the line and labels.

  • ShowLabel – Shows/hides trackball label. Default value is true.

  • ShowLine – Shows/hides the trackball line. Default value is true.

<chart:SfChart>
...

	<chart:SfChart.ChartBehaviors>

		<chart:ChartTrackballBehavior ShowLabel="True" ShowLine="True"/>

	</chart:SfChart.ChartBehaviors>

</chart:SfChart>
SfChart chart = new SfChart();
...

ChartTrackballBehavior trackballBehavior = new ChartTrackballBehavior();

trackballBehavior.ShowLabel = true;

trackballBehavior.ShowLine = true;

chart.ChartBehaviors.Add(trackballBehavior);

Trackball support in Xamarin.Forms Chart

Label Display Mode

TrackballLabelDisplayMode property is used to specify whether to display label for all the data points along the vertical line or display only single label. Following are the two options you can set to this property,

  • FloatAllPoints – Displays label for all the data points along the vertical line.
  • NearestPoint – Displays label for single data point that is nearer to the touch contact position.
  • GroupAllPoints – Displays label for all the data points grouped and positioned at the top of the chart area.
<chart:ChartTrackballBehavior LabelDisplayMode="NearestPoint" ShowLine="False"/>
ChartTrackballBehavior trackballBehavior = new ChartTrackballBehavior();

trackballBehavior.ShowLine = false;

trackballBehavior.LabelDisplayMode = TrackballLabelDisplayMode.NearestPoint;

In the following screenshot, trackball label is shown for only single data point,

Label display mode support for trackball in Xamarin.Forms Chart

Activation mode

The ActivationMode property is used to restrict the visibility of trackball based on the touch actions. The default value of this property is ChartTrackballActivationMode.LongPress.

The ChartTrackballActivationMode enum contains the following values:

  • LongPress – Activates trackball only when performing the long press action.
  • TouchMove – Activates trackball only when performing touch move action.
  • None – Hides the visibility of trackball when setting activation mode to None. It will be activated when calling the Show method.

NOTE

The default value of ActivationMode property is ChartTrackballActivationMode.LongPress for Android and iOS platform and default value for MacOS and UWP platform is ChartTrackballActivationMode.TouchMove.

Customizing appearance

Customize Trackball Labels

The LabelStyle property provides options to customize the trackball labels.

  • BorderColor – used to change the label border color.
  • BackgroundColor – used to change the label background color.
  • BorderThickness – used to change label border thickness.
  • TextColor – used to change the text color.
  • Font – used to change label font size, family and weight.
<chart:SfChart>
...

	<chart:SfChart.ChartBehaviors>

		<chart:ChartTrackballBehavior>

			<chart:ChartTrackballBehavior.LabelStyle>

				<chart:ChartTrackballLabelStyle BorderColor="Maroon" BackgroundColor="Aqua" BorderThickness="2" TextColor="Red" Font="Italic,18"/>

			</chart:ChartTrackballBehavior.LabelStyle>

		</chart:ChartTrackballBehavior>

	</chart:SfChart.ChartBehaviors>

</chart:SfChart>
SfChart chart = new SfChart();
...

ChartTrackballBehavior trackBallBehavior = new ChartTrackballBehavior();

trackBallBehavior.LabelStyle.BorderColor = Color.Maroon;

trackBallBehavior.LabelStyle.BorderThickness = 2;

trackBallBehavior.LabelStyle.Font = Font.SystemFontOfSize(18, FontAttributes.Italic);

trackBallBehavior.LabelStyle.BackgroundColor = Color.Aqua;

trackBallBehavior.LabelStyle.TextColor = Color.Red;

chart.ChartBehaviors.Add(trackballBehavior);

Customize Trackball Marker

The MarkerStyle property provides options to customize the trackball markers.

Following properties are used to customize the trackball marker.

  • ShowMarker – used to enable / disable the marker. Default value is true.
  • BorderColor – used to change the marker border color.
  • Color – used to change the marker background color.
  • BorderWidth – used to change the width of the marker border.
  • Width – used to change the width of the marker.
  • Height – used to change the height of the marker.
<chart:SfChart HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand">
...

	<chart:SfChart.ChartBehaviors>

		<chart:ChartTrackballBehavior>

			<chart:ChartTrackballBehavior.MarkerStyle>

				<chart:ChartTrackballMarkerStyle BorderColor="Purple" ShowMarker="True" BorderWidth="1" Width="8" Height="8" Color="Green"/>

			</chart:ChartTrackballBehavior.MarkerStyle>

		</chart:ChartTrackballBehavior>

	</chart:SfChart.ChartBehaviors>

</chart:SfChart>
SfChart chart = new SfChart();
...

ChartTrackballBehavior trackBallBehavior = new ChartTrackballBehavior();

trackBallBehavior.MarkerStyle.BorderWidth = 1;

trackBallBehavior.MarkerStyle.BorderColor = Color.Purple;

trackBallBehavior.MarkerStyle.Width = 8;

trackBallBehavior.MarkerStyle.Height = 8;

trackBallBehavior.MarkerStyle.Color = Color.Green;

trackBallBehavior.MarkerStyle.ShowMarker = true;

chart.ChartBehaviors.Add(trackballBehavior);

Customize Trackball Line

The LineStyle property provides options to customize the trackball line.

  • ShowLine – used to enable / disable the line. Default value is true.
  • StrokeWidth – used to change the stroke width of the line.
  • StrokeColor – used to change the stroke color of the line.
  • StrokeDashArray – Specifies the dashes to be applied on the line.
<chart:SfChart HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand">
...

	<chart:SfChart.ChartBehaviors>

		<chart:ChartTrackballBehavior>

			<chart:ChartTrackballBehavior.LineStyle>

				<chart:ChartLineStyle StrokeColor="Blue" StrokeWidth="2"/>

			</chart:ChartTrackballBehavior.LineStyle>

		</chart:ChartTrackballBehavior>

	</chart:SfChart.ChartBehaviors>

</chart:SfChart>
SfChart chart = new SfChart();
...

ChartTrackballBehavior trackBallBehavior = new ChartTrackballBehavior();

trackBallBehavior.ShowLine = true;

trackBallBehavior.LineStyle.StrokeWidth = 2;

trackBallBehavior.LineStyle.StrokeColor = Color.Blue;

trackBallBehavior.LineStyle.StrokeDashArray = new double[2] { 2, 3 };

chart.ChartBehaviors.Add(trackballBehavior);

Following screenshot illustrates the customization of trackball elements.

Customizing the appearance of trackball label in Xamarin.Forms Chart

Show/hide the trackball label in axis

This feature is used to highlight the respective axis label when the trackball is moving across the axis. ChartAxis.ShowTrackballInfo property is used show/hide the trackball label of the axis. ChartAxis.TrackballLabelStyle property is used to customize its appearance. Default value of ChartAxis.ShowTrackballInfo is False.

<chart:SfChart.PrimaryAxis >

    <chart:CategoryAxis ShowTrackballInfo = "true" />

</chart:SfChart.PrimaryAxis >
chart.PrimaryAxis.ShowTrackballInfo = true;

Showing and hiding the trackball label for axis in Xamarin.Forms Chart

Axis label alignment

The position of trackball’s axis label can be changed using the AxisLabelAlignment property of ChartTrackballAxisLabelStyle. The following options are available in AxisLabelAlignment.

  • Far - The label will be positioned below the tick in vertical axis and right of the tick in horizontal axis.
  • Near - The label will be positioned above the tick in vertical axis and left of the tick in horizontal axis.
  • Center - The label will be positioned at the center of tick. This is the default value.

The following code snippet and screenshot demonstrate the placement of label at the left to tick line.

<chart:SfChart>
 ...
<chart:CategoryAxis.TrackballLabelStyle>

    <chart:ChartTrackballAxisLabelStyle AxisLabelAlignment="Near"/>

</chart:CategoryAxis.TrackballLabelStyle>
 ...
</chart:SfChart>
primaryAxis.TrackballLabelStyle.AxisLabelAlignment = ChartLabelAlignment.Near;

Label alignment support for trackball axis label in Xamarin.Forms Chart

Show/hide the series label

This feature is used to show/hide the trackball label of the series by using CartesianSeries.ShowTrackballInfo property. Default value of CartesianSeries.ShowTrackballInfo property is True.

<chart:SfChart>
...

    <chart:LineSeries ItemsSource ="{Binding Data}" XBindingPath="Year"
    YBindingPath="Value" ShowTrackballInfo = "false" />

</chart:SfChart>
SfChart chart = new SfChart();
...

LineSeries lineSeries = new LineSeries()
{
    ItemsSource = Data,
    XBindingPath = "Year",
    YBindingPath = "Value",
    ShowTrackballInfo = false

};
chart.Series.Add(lineSeries);

Showing and hiding the trackball label for series in Xamarin.Forms Chart

Label Template

You can customize the appearance of the Trackball label with your own template by using TrackballLabelTemplate property of ChartSeries.

<ContentPage.Resources>
    <ResourceDictionary>
       <DataTemplate x:Key="trackballTemplate">
          <StackLayout  Orientation="Horizontal">
             <Label  Text="{Binding Value}" TextColor="White" FontSize ="15" VerticalTextAlignment="Center"/>
             <Image Source ="grain.jpg" WidthRequest="30" HeightRequest="30"/>
          </StackLayout>
       </DataTemplate>
    </ResourceDictionary>
</ContentPage.Resources>

<chart:SfChart.Series>
    <chart:LineSeries TrackballLabelTemplate="{StaticResource trackballTemplate}" ItemsSource="{Binding Data1}" XBindingPath="Name" YBindingPath="Value"/>
    <chart:LineSeries TrackballLabelTemplate="{StaticResource trackballTemplate}" ItemsSource="{Binding Data2}" XBindingPath="Name" YBindingPath="Value"/>
</chart:SfChart.Series>

<chart:SfChart.ChartBehaviors>
    <chart:ChartTrackballBehavior/>
</chart:SfChart.ChartBehaviors>
SfChart chart = new SfChart ();
...

var lineSeries1 = new LineSeries();
lineSeries1.ItemsSource = Data1;
lineSeries1.XBindingPath = "Name";
lineSeries1.YBindingPath = "Value";

var lineSeries2 = new LineSeries();
lineSeries2.ItemsSource = Data2;
lineSeries2.XBindingPath = "Name";
lineSeries2.YBindingPath = "Value";

DataTemplate trackBallTemplate = new DataTemplate(() =>
{
     StackLayout stack = new StackLayout();
     stack.Orientation = StackOrientation.Horizontal;
     Label label = new Label();
     label.SetBinding(Label.TextProperty, "Value");
     label.FontSize = 15;
     label.VerticalTextAlignment = TextAlignment.Center;
     label.TextColor = Color.White;
     Image image = new Image();
     image.Source = "grain.jpg";
     image.WidthRequest = 30;
     image.HeightRequest = 30;
     stack.Children.Add(label);
     stack.Children.Add(image);
     return stack;
});

lineSeries1.TrackballLabelTemplate = trackBallTemplate;
lineSeries2.TrackballLabelTemplate = trackBallTemplate;

chart.Series.Add(lineSeries1);
chart.Series.Add(lineSeries2);

chart.ChartBehaviors.Add(new ChartTrackballBehavior());

Label template support for trackball in Xamarin.Forms Chart

Customize the Axis Label with DataTemplate

Customize the appearance of axis label of trackball using TrackballLabelTemplate property of ChartAxis.

<ContentPage.Resources>
    <ResourceDictionary>
      <DataTemplate x:Key="axisLabelTemplate">
        <Label WidthRequest="50" HeightRequest="20" HorizontalTextAlignment="Center" BackgroundColor="Blue" Text="{Binding }" TextColor="White" FontSize ="15" />
      </DataTemplate>
    </ResourceDictionary>
</ContentPage.Resources>

 <chart:SfChart.PrimaryAxis>
       <chart:CategoryAxis  ShowTrackballInfo="True" TrackballLabelTemplate="{StaticResource axisLabelTemplate}">
        <chart:CategoryAxis.TrackballLabelStyle>
          <chart:ChartTrackballAxisLabelStyle   BackgroundColor="Transparent"/>
        </chart:CategoryAxis.TrackballLabelStyle>  
      </chart:CategoryAxis>  
</chart:SfChart.PrimaryAxis>

<chart:SfChart.ChartBehaviors>
     <chart:ChartTrackballBehavior />
</chart:SfChart.ChartBehaviors>
Chart.PrimaryAxis = new CategoryAxis(); 
Chart.PrimaryAxis.ShowTrackballInfo = true;
Chart.PrimaryAxis.TrackballLabelStyle.BackgroundColor = Color.Transparent;
DataTemplate axisLabelTemplate = new DataTemplate(() =>
{              
     Label label = new Label();
     label.SetBinding(Label.TextProperty, ".");
     label.FontSize = 15;
     label.HorizontalTextAlignment = TextAlignment.Center;
     label.TextColor = Color.White;
     label.BackgroundColor = Color.Blue;                       
     label.WidthRequest = 50;
     label.HeightRequest = 20;           
     return label;
});
Chart.PrimaryAxis.TrackballLabelTemplate = axisLabelTemplate;
Chart.ChartBehaviors.Add(new ChartTrackballBehavior());

Template support for trackball axis label in Xamarin.Forms Chart

Methods

Show method

The Show method is used to activate the trackball at the specified location.

  • c#
  • trackball.Show(pointX, pointY);

    Hide method

    The Hide method is used to hide the trackball programmatically.

  • c#
  • trackball.Hide();

    HitTest method

    The HitTest method is used to check whether the point is in trackball or not.

  • c#
  • [C#]
    
    trackball.HitTest(pointX, pointY);

    Events

    TrackballCreated

    The TrackballCreated event occurs when the trackball moves from one data point to another. This argument contains object of ChartPointsInfo. The following properties are available in ChartPointInfo class to customize the appearance of trackball label based on condition.

    • Label - Gets or sets the text of trackball label.
    • IsVisible - Gets or sets the visibility of trackball.
    • Series - Gets the series of the data point in which trackball is activated.
    • LabelStyle - Customizes the appearance of trackball label.
    • DataPoint - Gets the respective underlying object of the data in which trackball is activated.
    • DataPointIndex - Gets the index of the selected data point.
    • XPosition - Gets the x-position of trackball label.
    • YPosition - Gets the y-position of trackball label.
    • BackgroundColor - Gets the default background color of trackball label.