styles - WPF: Alternating colors on a ItemsControl?

Question

How do I get alternating colors on a ItemsControl? I have AlternationCount set to 2, but the ItemsControl.AlternationIndex property always returns 0.

        <ItemsControl ItemsSource="{Binding}" AlternationCount="2">
            <ItemsControl.Resources>
                <Style x:Key="FooBar" TargetType="Grid">
                    <Style.Triggers>
                        <Trigger Property="ItemsControl.AlternationIndex" Value="0">
                            <Setter Property="Background" Value="Blue"/>
                        </Trigger>
                        <Trigger Property="ItemsControl.AlternationIndex" Value="1">
                            <Setter Property="Background" Value="Red"/>
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </ItemsControl.Resources>
            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <Grid Margin="0,0,0,10" Style="{StaticResource FooBar}">
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="25" />
                            <ColumnDefinition Width="100" />
                            <ColumnDefinition Width="100" />
                            <ColumnDefinition Width="100" />
                            <ColumnDefinition Width="100" />
                            <ColumnDefinition Width="100" />
                            <ColumnDefinition Width="100" />
                            <ColumnDefinition Width="*" />
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions >
                            <RowDefinition Height="Auto" />
                            <!--<RowDefinition Height="Auto" />-->
                        </Grid.RowDefinitions>

                        <CheckBox IsChecked="{Binding Checked, UpdateSourceTrigger=PropertyChanged}" VerticalAlignment="Center" />
                        <Label Grid.Column="1" Content="{Binding CompanyName}" />
                        <Label Grid.Column="2" Content="{Binding TradeKey}" />
                        <Label Grid.Column="3" Content="{Binding TradeDate}" ContentStringFormat="d" />
                        <Label Grid.Column="4" Content="{Binding Cusip}" />
                        <Label Grid.Column="5" Content="{Binding IssueName}" />
                        <Label Grid.Column="6" Content="{Binding TotalUnits}" ContentStringFormat="N0" />

                        <!--<Expander Grid.Row="0" Grid.Column="7" Grid.ColumnSpan="7" IsExpanded="True">
                            <Expander.Header>
                                <StackPanel Orientation="Horizontal">
                                    <Label Content="Allocations"/>
                                    <Button Content="Edit" Name="cmdEdit" Click="cmdEdit_Click"  />
                                </StackPanel>
                            </Expander.Header>-->
                        <DataGrid Grid.Column="7" IsReadOnly="True" ItemsSource="{Binding Territories}" AutoGenerateColumns="False" CanUserAddRows="False" CanUserDeleteRows="False">
                            <DataGrid.Columns>
                                <DataGridTextColumn Header="Rep on Ticket" Binding="{Binding TradeCustomer.RepNameNotes}" />
                                <DataGridTextColumn Header="Rep # on Ticket" Binding="{Binding TradeCustomer.RepNumberNotes}" />
                                <DataGridTextColumn Header="State" Binding="{Binding TradeCustomer.AccountStateKey}" />
                                <DataGridTextColumn Header="Qty. on Ticket" Binding="{Binding TradeCustomer.Quantity, StringFormat=N0}" />

                                <DataGridTextColumn Header="Zip Code" Binding="{Binding ZipCode}" />
                                <DataGridTextColumn Header="State" Binding="{Binding State}" />
                                <DataGridTextColumn Header="Territory" Binding="{Binding Territory}" />

                            </DataGrid.Columns>

                        </DataGrid>
                        <!--</Expander>-->

                    </Grid>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <VirtualizingStackPanel />
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>
            <ItemsControl.Template>
                <ControlTemplate>
                    <Border BorderThickness="{TemplateBinding Border.BorderThickness}" Padding="{TemplateBinding Control.Padding}" BorderBrush="{TemplateBinding Border.BorderBrush}" Background="{TemplateBinding Panel.Background}" SnapsToDevicePixels="True">
                        <ScrollViewer Padding="{TemplateBinding Control.Padding}" Focusable="False">
                            <ItemsPresenter SnapsToDevicePixels="{TemplateBinding UIElement.SnapsToDevicePixels}" />
                        </ScrollViewer>
                    </Border>
                </ControlTemplate>
            </ItemsControl.Template>
        </ItemsControl>

Answer 1

Check here http://www.codeproject.com/Articles/35886/WPF-ItemsControl-with-alternating-items-and-hover-.aspx

You have to change your code like this to get it working

    <ItemsControl ItemsSource="{Binding DataList}" AlternationCount="2">
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Grid x:Name="FooBar" Margin="0,0,0,10">                    
                   ----------------------------
                   ----------------------------
                </Grid>
                <DataTemplate.Triggers>
                    <Trigger Property="ItemsControl.AlternationIndex" Value="0">
                        <Setter Property="Background" Value="Blue" TargetName="FooBar"/>
                    </Trigger>
                    <Trigger Property="ItemsControl.AlternationIndex" Value="1">
                        <Setter Property="Background" Value="Red" TargetName="FooBar"/>
                    </Trigger>
                </DataTemplate.Triggers>
            </DataTemplate>
        </ItemsControl.ItemTemplate>