Did you properly merge in all the changes from the sample I posted? It sounds like you are not setting the LegendItemTemplate

-Graham

There is no luck, it shows "Series Title".

By the way, I am getting a problem that I have posted in this forum, that when I ask my server to change the data to show, it does not paint any bar, and I have realized that the legend neither changes. I know this because it must show 4 elements when I change my detail option and it continues showing 6 of my default choice.

Looks like there is a bit of a functionality hole there for the auto generated case. I couldn't find a straightforward way to make the series title equal the key for that series.
So you may want to make a feature request. But you can do the below to work around the missing functionality.

<UserControl.Resources>
        <local:TestEmissionsCollection x:Key="data" />
        <igChart:GroupBy 
            x:Key="grouped"
            ItemsSource="{StaticResource data}" 
            GroupMemberPath="Date" 
            KeyMemberPath="Installation" 
            ValueMemberPath="Emission" />
        
        <local:KeyConverter x:Key="keyConverter" />
        
        <DataTemplate x:Key="keyLegendItemTemplate">
            <StackPanel Orientation="Horizontal" Margin="1" Visibility="{Binding Series.Visibility}">
                <ContentPresenter Content="{Binding}" ContentTemplate="{Binding Series.LegendItemBadgeTemplate}" />
                <ContentPresenter Content="{Binding Series.ValueMemberPath, Converter={StaticResource keyConverter}, ConverterParameter='_Emission'}"/>
            </StackPanel>
        </DataTemplate>
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot" Background="White">
        <Grid.ColumnDefinitions>
            <ColumnDefinition />
            <ColumnDefinition Width="Auto" />
        </Grid.ColumnDefinitions>
        <igChart:XamDataChart x:Name="theChart"
                              Legend="{Binding ElementName=legend1}">
            <igChart:XamDataChart.Axes>
                <igChart:CategoryXAxis x:Name="xAxis" 
                                       ItemsSource="{StaticResource grouped}"
                                       Label="{}{Key}"/>
                <igChart:NumericYAxis x:Name="yAxis" />
            </igChart:XamDataChart.Axes>

            <igChart:XamDataChart.Series>
                <igChart:StackedColumnSeries x:Name="stack"
                                             ItemsSource="{StaticResource grouped}"
                                             XAxis="{Binding ElementName=xAxis}"
                                             YAxis="{Binding ElementName=yAxis}"
                                             AutoGenerateSeries="True"
                                             LegendItemTemplate="{StaticResource keyLegendItemTemplate}"
                                             >
                   
                </igChart:StackedColumnSeries>
            </igChart:XamDataChart.Series>
        </igChart:XamDataChart>
        
        <igChart:Legend x:Name="legend1" Grid.Column="1" />
    </Grid>
</UserControl>

And code behind:

 public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();
        }
    }

    public class TestEmissionsCollection
        : ObservableCollection<InstalationEmissionDateInformation>
    {
        public TestEmissionsCollection()
        {
            Add(new InstalationEmissionDateInformation("A", 5, "1/1/2012", 1));
            Add(new InstalationEmissionDateInformation("B", 2, "1/1/2012", 1));
            Add(new InstalationEmissionDateInformation("C", 7, "1/1/2012", 1));
            Add(new InstalationEmissionDateInformation("A", 6, "1/2/2012", 1));
            Add(new InstalationEmissionDateInformation("B", 3, "1/2/2012", 1));
            Add(new InstalationEmissionDateInformation("C", 8, "1/2/2012", 1));
            Add(new InstalationEmissionDateInformation("A", 6, "1/3/2012", 1));
            Add(new InstalationEmissionDateInformation("B", 3, "1/3/2012", 1));
            Add(new InstalationEmissionDateInformation("C", 6, "1/3/2012", 1));
            Add(new InstalationEmissionDateInformation("A", 4, "1/4/2012", 1));
            Add(new InstalationEmissionDateInformation("B", 3, "1/4/2012", 1));
            Add(new InstalationEmissionDateInformation("C", 7, "1/4/2012", 1));
        }
    }

    public class InstalationEmissionDateInformation
    {
        public string Installation { get; set; }
        public Decimal Emission { get; set; }
        public string Date { get; set; }
        public Decimal Assignation { get; set; }

        public InstalationEmissionDateInformation(
            string installation, 
            Decimal emission, 
            string date, 
            Decimal assignation)
        {
            Installation = installation;
            Emission = emission;
            Date = date;
            Assignation = assignation;
        }
    }

    public class KeyConverter
        : IValueConverter
    {

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (value is string && parameter is string)
            {
                var key = (string)value;
                var param = (string)parameter;

                key = key.Replace(param, "");

                return key;
            }

            return "";
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

Hope this helps!
-Graham

My second question, I have this legend and I don't know how to bind the context to my GroupByItems. i want to show the KeyMemberPath name in my legend.

Legend:

<ig:Legend x:Name="xmLegend" 

HorizontalAlignment="Stretch" 

Background="Transparent" Padding="2"

BorderBrush="Transparent" 

Style="{x:Null}" 

VerticalAlignment="Top" 

Margin="2"

Content="{Binding Source={StaticResource grouped},Path= KeyMemberPath}">
</ig:Legend>

Groupby:

<igChart:GroupBy
            x:Key="grouped"
            ItemsSource="{Binding ValuesOfExcessVsEmissions,Mode=TwoWay}"
            GroupMemberPath="Date"
            KeyMemberPath="Name"
            ValueMemberPath="Total"/>

Its not against the pattern, have something in your viewmodel listen to the event and change a visibility property on the viewmodel accordingly. Then have the chart or a splash bind to the visibility property on your viewmodel.

You will have to explain what you mean by the second question in more detail.

Hope this helps!

-Graham