ILegendItemProvider Interface

An interface that a point or segment colorizer should implement to specify legend items.

Namespace: DevExpress.XamarinForms.Charts

Assembly: DevExpress.XamarinForms.Charts.dll

NuGet Package: DevExpress.XamarinForms.Charts

Declaration

public interface ILegendItemProvider

Related API Members

The following members return ILegendItemProvider objects:

• ICustomPointColorizer.GetLegendItemProvider()
• IIndexBasedCustomPointColorizer.GetLegendItemProvider()
• IRangeCustomPointColorizer.GetLegendItemProvider()
• IStackedCustomPointColorizer.GetLegendItemProvider()
• IWeightedCustomPointColorizer.GetLegendItemProvider()

Remarks

A colorizer class that implements the ILegendItemProvider interface should implement the following methods:

• GetLegendItemCount - returns the number of items in a legend.
• GetLegendItem - returns a CustomLegendItem object that specifies text and marker color for each item in a legend.

Example

In this example, the bar chart visualizes GDP values for the G20 and colors data points according to which part of the world the country belongs.

1. Create a data source – a list of objects each of which stores a country’s name, GDP value, and the part of the world (region) where the country is located.

2. Create a class (ColorizerByRegion, in this example) that implements the IIndexBasedCustomPointColorizer interface. Specify a color for each region and implement the IIndexBasedCustomPointColorizer.GetColor method that returns a color for each data point depending on the Region data member’s value.
   This class should also implement the IIndexBasedCustomPointColorizer.GetLegendItemProvider method and the ILegendItemProvider interface to specify legend items that show region colors.

   C#

   using Xamarin.Forms;
   using System.Collections.Generic;
   using DevExpress.XamarinForms.Charts;
   
   namespace ColorizerExample {
       public class ViewModel {
           CountryStatisticsData data = new CountryStatisticsData();
           public List<CountryStatistics> CountryStatisticsData => this.data.SeriesData;
       }
   
       public class CountryStatisticsData {
           readonly List<CountryStatistics> data = new List<CountryStatistics> {
               new CountryStatistics("Argentina", 16011.6728032264, "America"),
               new CountryStatistics("Australia", 38159.6336533223, "Australia"),
               new CountryStatistics("Brazil", 11210.3908053823, "America"),
               new CountryStatistics("Canada", 39050.1673163719, "America"),
               new CountryStatistics("China", 7599, "Asia"),
               new CountryStatistics("France", 34123.1966249035, "Europe"),
               new CountryStatistics("Germany", 37402.2677660974, "Europe"),
               new CountryStatistics("India", 3425.4489267524, "Asia"),
               new CountryStatistics("Indonesia", 4325.2533282173, "Asia"),
               new CountryStatistics("Italy", 31954.1751781228, "Europe"),
               new CountryStatistics("Japan", 33732.8682226596, "Asia"),
               new CountryStatistics("Mexico", 14563.884253986, "America"),
               new CountryStatistics("Russia", 19891.3528339013, "Europe"),
               new CountryStatistics("Saudi Arabia", 22713.4852913284, "Asia"),
               new CountryStatistics("South Africa", 10565.1840563081, "Africa"),
               new CountryStatistics("South Korea", 29101.0711400706, "Asia"),
               new CountryStatistics("Turkey", 15686.860167575, "Africa"),
               new CountryStatistics("United Kingdom", 35686.1997705521, "Europe"),
               new CountryStatistics("Spain", 32230.3585974199, "Europe"),
               new CountryStatistics("USA", 47153.0094273427, "America"),
           };
           public List<CountryStatistics> SeriesData => this.data;
       }
   
       public class CountryStatistics {
           public string Country { get; private set; }
           public double Gdp { get; private set; }
           public string Region { get; private set; }
   
           public CountryStatistics(string country, double gdp, string region) {
               Country = country;
               Gdp = gdp;
               Region = region;
           }
       }
   
       public class ColorizerByRegion : IIndexBasedCustomPointColorizer, ILegendItemProvider {
           private CountryStatisticsData data = new CountryStatisticsData();
           private Dictionary<string, Color> colors = new Dictionary<string, Color> {
               {"Africa", Color.FromHex("5b9bd5")},
               {"America",  Color.FromHex("ed7d31")},
               {"Asia", Color.FromHex("a5a5a5")},
               {"Australia", Color.FromHex("ffc000")},
               {"Europe", Color.FromHex("4472c4")}
           };
           private List<string> regions = new List<string> {
               "Africa", "America", "Asia", "Australia", "Europe"
           };
   
           public Color GetColor(int index) {
               return colors[data.SeriesData[index].Region];
           }
   
           public CustomLegendItem GetLegendItem(int index) {
               return new CustomLegendItem(regions[index], colors[regions[index]]);
           }
   
           public int GetLegendItemCount() {
               return regions.Count;
           }
   
           public ILegendItemProvider GetLegendItemProvider() {
               return this;
           }
       }
   }
   

3. Assign a ColorizerByRegion object to the BarSeries.PointColorizer property.

   XAML

   <ContentPage
       xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
       xmlns:dxc="http://schemas.devexpress.com/xamarin/2014/forms/charts"
       x:Class="ColorizerExample.MainPage"
       xmlns:local="clr-namespace:ColorizerExample">
       <ContentPage.BindingContext>
           <local:ViewModel/>
       </ContentPage.BindingContext>
       <dxc:ChartView Rotated="True">
           <dxc:ChartView.Series>
               <dxc:BarSeries PointColorizer="{local:ColorizerByRegion}">
                   <!-- Bind the series to the data source. -->
                   <dxc:BarSeries.Data>
                       <dxc:SeriesDataAdapter DataSource="{Binding CountryStatisticsData}"
                                              ArgumentDataMember="Country">
                           <dxc:ValueDataMember Type="Value" Member="Gdp"/>
                       </dxc:SeriesDataAdapter>
                   </dxc:BarSeries.Data>
               </dxc:BarSeries>
           </dxc:ChartView.Series>
   
           <!-- Specify axis and legend settings here. -->
       </dxc:ChartView>
   </ContentPage>
   

   View Example