Customize PieChart Series Text, Color and FontSize

Environment

Version	Product	Author
6.6.0	Telerik UI for .NET MAUI Chart	Dobrinka Yordanova

Description

This article described how to customize the text, color, font size of the chart PieSeries.

Solution

For this purpose you have to use the native chart.

1. Chart definition in XAML

<telerik:RadPieChart x:Name="chart" HandlerChanged="chart_HandlerChanged">
    <telerik:RadPieChart.BindingContext>
        <local:ViewModel />
    </telerik:RadPieChart.BindingContext>
    <telerik:RadPieChart.Series>
        <telerik:PieSeries ShowLabels="True"
                    RadiusFactor="0.8"
                    ValueBinding="Value"
                    ItemsSource="{Binding Data}" />
    </telerik:RadPieChart.Series>
</telerik:RadPieChart>

2. The namespace

xmlns:telerik="http://schemas.telerik.com/2022/xaml/maui"

3. DataModel and ViewModel

public class CategoricalData
{
    public object Category { get; set; }
    public double Value { get; set; }
}

public class ViewModel
{
    public ObservableCollection<CategoricalData> Data { get; set; }

    public ViewModel()
    {
        this.Data = GetCategoricalData();
    }

    private static ObservableCollection<CategoricalData> GetCategoricalData()
    {
        var data = new ObservableCollection<CategoricalData>
    {
        new CategoricalData { Category = "Greenings", Value = 52 },
        new CategoricalData { Category = "Perfecto", Value = 19 },
        new CategoricalData { Category = "NearBy", Value = 82 },
        new CategoricalData { Category = "Family", Value = 23 },
        new CategoricalData { Category = "Fresh", Value = 56 },
    };
        return data;
    }
}

4. Subscribe to the Chart.HandlerChanged event to access the native chart and implement the customizations per platform:

private void chart_HandlerChanged(object sender, EventArgs e)
{
    this.UpdateChart();
}

private void UpdateChart()
{
    var platformView = this.chart.Handler.PlatformView;

    // Implementation on Android
#if ANDROID
    var platformChart = (Com.Telerik.Widget.Chart.Visualization.PieChart.RadPieChartView)platformView;
    var platformSeries = (Com.Telerik.Widget.Chart.Visualization.PieChart.PieSeries)platformChart.Series.Get(0);

    platformSeries.LabelFillColor = Android.Graphics.Color.Red;
    platformSeries.LabelTextColor = Android.Graphics.Color.Blue;

// Implementation on MacCatalyst and iOS
#elif IOS || MACCATALYST
    var platformChart = (Telerik.Maui.Controls.Compatibility.ChartRenderer.iOS.TKExtendedChart)platformView;
    var platformSeries = (TelerikUI.TKChartPieSeries)platformChart.Series[0];
    platformSeries.Style.PointLabelStyle.TextColor = UIKit.UIColor.Green;
    platformSeries.Style.PointLabelStyle.TextHidden = false;
    platformSeries.Style.PointLabelStyle.StringFormat = "$ %.0f";

    // Implementation on WInUI
#elif WINDOWS
    var platformChart = (Telerik.UI.Xaml.Controls.Chart.RadPieChart)platformView;
    var platformSeries = (Telerik.UI.Xaml.Controls.Chart.PieSeries)platformChart.Series[0];
    platformSeries.LabelDefinitions.Clear();
    platformSeries.LabelDefinitions.Add(new Telerik.UI.Xaml.Controls.Chart.ChartSeriesLabelDefinition 
    { 

        LabelTemplate = MauiWinUIApplication.Current.Resources["PieLabelTemplate"] as Microsoft.UI.Xaml.DataTemplate
});
#endif
}

5. Define the PieLabelTemplate inside the Platforms/Windows/App.xaml file:

<maui:MauiWinUIApplication
    x:Class="ShellApp.WinUI.App"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:maui="using:Microsoft.Maui"
    xmlns:local="using:ShellApp.WinUI">
    <maui:MauiWinUIApplication.Resources>
        <ResourceDictionary>
            <DataTemplate x:Key="PieLabelTemplate">
                <Grid Background="Red">
                    <TextBlock Text="{Binding DataItem.Value}"
                               Foreground="White"
                               FontWeight="Bold"
                               FontSize="10"
                               Margin="5" />
                </Grid>
            </DataTemplate>
        </ResourceDictionary>
    </maui:MauiWinUIApplication.Resources>
</maui:MauiWinUIApplication>