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How to create custom legend items in WPF Chart?

Platform: WPF |
Control: SfChart

This article describes how to define the custom legend items with view model data. 

 

Custom legend items are achieved by adding required LegendItem count to ChartLegend’s Items property with Item, Series, IconHeight, IconWidth, IconVisibility, Interior and ItemTemplate as per the below code snippet

 

[XAML]

 

<DataTemplate x:Key="itemTemplate"> 
        <StackPanel Margin="10,0,10,0"  Orientation="Horizontal"> 
                    <CheckBox Margin="2" Tag="{Binding}" 
                              IsChecked="True" 
                              Checked="CheckBox_Checked"   
                              Unchecked="CheckBox_Unchecked"/> 
 
                    <Rectangle  Width="{Binding IconWidth}"  
                                Height="{Binding IconHeight}"                                         
                                Fill="{Binding Interior}" Margin="2"/> 
 
                    <TextBlock HorizontalAlignment="Center" 
                               Margin="5,0,0,0" 
                               VerticalAlignment="Center" 
                               Text="{Binding Item.XValue}"> 
 
                    </TextBlock> 
          </StackPanel> 
</DataTemplate> 

 

[C#]

 

          ChartLegend legend = new ChartLegend(); 
 
            foreach (var series in chart.Series) 
            { 
                var data = series.ItemsSource as ObservableCollection<Model>; 
                for (int i = 0; i < data.Count; i++) 
                { 
                    legend.Items.Add(new LegendItem() 
                    { 
                        Item = data[i].XValue.ToString(), 
                        Series = series, 
                        IconHeight = 10, 
                        IconWidth = 10, 
                        IconVisibility = Visibility.Visible, 
                        Interior = series1.ColorModel.GetBrush(i),
                        CheckBoxVisibility = Visibility.Visible
                    }); 
                } 
            } 
 
            legend.ItemTemplate = grid.Resources["itemTemplate"] as DataTemplate; 
            chart.Legend = legend; 

 

        private void CheckBox_Checked(object sender, RoutedEventArgs e) 
        { 
            CheckBox box = sender as CheckBox; 
            LegendItem item = box.Tag as LegendItem; 
 
            UpdateLegend(true, item.Item as Model); 
        } 
 
        private void CheckBox_Unchecked(object sender, RoutedEventArgs e) 
        { 
            CheckBox box = sender as CheckBox; 
            LegendItem item = box.Tag as LegendItem; 
 
            UpdateLegend(false, item.Item as Model); 
        } 
 
        private void UpdateLegend(bool isChecked, Model item) 
        { 
            foreach (PieSeriesExt series in chart.Series) 
            { 
                if (isChecked) 
                    toggleIndexes.Remove(viewModel.Data.IndexOf(item)); 
                else 
                    toggleIndexes.Add(viewModel.Data.IndexOf(item)); 
 
                series.GetType().GetField("ToggledLegendIndex", BindingFlags.NonPublic | 
                    BindingFlags.Instance).SetValue(series, toggleIndexes); 
            } 
 
            UpdateArea(); 
        } 
 
        private void UpdateArea() 
        { 
            MethodInfo info = chart.GetType().GetMethod("UpdateArea", 
                               BindingFlags.NonPublic | BindingFlags.Instance, 
                               null, 
                               new Type[] { typeof(bool) }, 
                               null); 
 
            info?.Invoke(chart, new object[] { true }); 
        } 

Output

Before custom legend toggling


After custom legend togglinng  

Download complete sample here.

 

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Comments
Brent Hoskisson
Sep 15, 2021

You have item.Item as Model. What is Model????

Thanks

Reply

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