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MainWindow.xaml

<Window x:Class="WpfApp39.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp39"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="600">
    <Window.Resources>

        <Style TargetType="{x:Type Line}" x:Key="DataGridRow.Line">
            <Setter Property="Visibility" Value="Collapsed" />
            <Setter Property="Stroke" Value="Red" />
            <Setter Property="StrokeThickness" Value="2" />
            <Setter Property="VerticalAlignment" Value="Center" />
        </Style>

        <Style TargetType="{x:Type DataGridRow}" x:Key="dataGridRowStyle">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type DataGridRow}">
                        <Border x:Name="DGR_Border" BorderBrush="{TemplateBinding BorderBrush}"
                                        BorderThickness="{TemplateBinding BorderThickness}" 
                                        Background="{TemplateBinding Background}"
                                        SnapsToDevicePixels="True">
                            <SelectiveScrollingGrid>
                                <SelectiveScrollingGrid.ColumnDefinitions>
                                    <ColumnDefinition Width="Auto"/>
                                    <ColumnDefinition Width="*"/>
                                </SelectiveScrollingGrid.ColumnDefinitions>
                                <SelectiveScrollingGrid.RowDefinitions>
                                    <RowDefinition Height="*"/>
                                    <RowDefinition Height="Auto"/>
                                </SelectiveScrollingGrid.RowDefinitions>

                                <DataGridCellsPresenter x:Name="cellsPresenter" Grid.Column="1" 
                                                        ItemsPanel="{TemplateBinding ItemsPanel}" 
                                                        SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                                <DataGridDetailsPresenter Grid.Column="1" Grid.Row="1" 
                                                          SelectiveScrollingGrid.SelectiveScrollingOrientation="{Binding AreRowDetailsFrozen, ConverterParameter={x:Static SelectiveScrollingOrientation.Vertical}, Converter={x:Static DataGrid.RowDetailsScrollingConverter}, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}" 
                                                          Visibility="{TemplateBinding DetailsVisibility}"/>

                                <!-- DataGridRowの中にLineを配置 -->
                                <Line x:Name="line" Grid.Column="1" Style="{DynamicResource ResourceKey=DataGridRow.Line}"
                                      X2="{Binding ElementName=cellsPresenter,Path=ActualWidth}" />

                                <DataGridRowHeader Grid.RowSpan="2" 
                                                   SelectiveScrollingGrid.SelectiveScrollingOrientation="Vertical" 
                                                   Visibility="{Binding HeadersVisibility, ConverterParameter={x:Static DataGridHeadersVisibility.Row}, Converter={x:Static DataGrid.HeadersVisibilityConverter}, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"/>

                            </SelectiveScrollingGrid>
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>

    </Window.Resources>

    <Grid>
        <DataGrid ItemContainerStyle="{StaticResource ResourceKey=dataGridRowStyle}"
                  ItemsSource="{Binding}" DataContext="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                  HeadersVisibility="All" RowHeaderWidth="30" CanUserResizeColumns="True" >

            <DataGrid.Resources>
                <Style TargetType="{x:Type Line}" x:Key="DataGridRow.Line" BasedOn="{StaticResource ResourceKey=DataGridRow.Line}">
                    <Style.Triggers>

                        <DataTrigger Binding="{Binding}" Value="A" >
                            <Setter Property="Visibility" Value="Visible" />
                        </DataTrigger>

                        <DataTrigger Binding="{Binding}" Value="G" >
                            <Setter Property="Visibility" Value="Visible" />
                            <Setter Property="Stroke" Value="#7F00FF00" />
                        </DataTrigger>

                        <DataTrigger Binding="{Binding}" Value="B" >
                            <Setter Property="Visibility" Value="Visible" />
                            <Setter Property="Stroke" Value="#7F0000FF" />
                            <Setter Property="VerticalAlignment" Value="Bottom" />
                            <Setter Property="Margin" Value="0,0,0,3" />
                            <!--<Setter Property="X1" Value="50" />-->
                        </DataTrigger>

                        <DataTrigger Binding="{Binding RelativeSource={RelativeSource Mode=TemplatedParent},Path=IsMouseOver}" Value="True">
                            <Setter Property="StrokeThickness" Value="5" />
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </DataGrid.Resources>

            <DataGrid.Columns>
                <DataGridTextColumn Header="Column1" IsReadOnly="true" Binding="{Binding Mode=OneWay}" />
                <DataGridTextColumn Header="Column2" IsReadOnly="true" Binding="{Binding Mode=OneWay}" />
                <DataGridTextColumn Header="Column3" IsReadOnly="true" Binding="{Binding Mode=OneWay}" Width="500"/>
                <DataGridTextColumn Header="Column4" IsReadOnly="true" Binding="{Binding Mode=OneWay}" />
                <DataGridTextColumn Header="Column5" IsReadOnly="true" Binding="{Binding Mode=OneWay}" />
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>