WPF treeview item background over entire row

Question 1

Use snoop to understand the visual tree you are trying to modify. This way it will take 2-3 minutes to actually know what you need to modify. ( google )

My bet is that you need to use something like this:

<TreeView>
<TreeView.ItemContainerStyle>
<Style BasedOn="{StaticResource {x:Type TreeViewItem}}" TargetType="TreeViewItem">
                    <Setter Property="Background" Value="Purple" />
</TreeView.ItemContainerStyle>
</TreeView>

you will also need to add triggers if you want background colo depending on items.

Question 2

Thanks for your solution! Here's is a preview what I've done so far:

preview

<TreeView Grid.Row="1"  Name="treeView" Margin="5">
    <TreeView.ItemContainerStyle>
        <Style TargetType="{x:Type TreeViewItem}">
            <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
            <Setter Property="KeyboardNavigation.AcceptsReturn" Value="True" />
            <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />
            <!-- Style for the selected item -->
            <Setter Property="BorderThickness" Value="1"/>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type TreeViewItem}">
                        <ControlTemplate.Resources>
                            <Conv:LeftMarginMultiplierConverter Length="19" x:Key="lengthConverter" />
                        </ControlTemplate.Resources>
                        <StackPanel>
                            <Border 
                                x:Name="Bd"
                                Background="{TemplateBinding Background}"
                                BorderBrush="{TemplateBinding BorderBrush}"
                                BorderThickness="{TemplateBinding BorderThickness}"
                                Padding="{TemplateBinding Padding}">
                                <Grid Margin="{Binding Converter={StaticResource lengthConverter}, RelativeSource={RelativeSource TemplatedParent}}">
                                    <Grid.ColumnDefinitions>
                                        <ColumnDefinition Width="19" />
                                        <ColumnDefinition/>
                                    </Grid.ColumnDefinitions>
                                    <ToggleButton 
                                        Grid.Column="0" 
                                        x:Name="Expander"
                                        Style="{StaticResource ExpandCollapseToggleStyle}"
                                        IsChecked="{Binding Path=IsExpanded, RelativeSource={RelativeSource TemplatedParent}}"
                                        ClickMode="Press"/>
                                    <ContentPresenter x:Name="PART_Header" Grid.Column="1" VerticalAlignment="Stretch" HorizontalAlignment="Stretch" ContentSource="Header" />
                                </Grid>
                            </Border>
                            <ItemsPresenter x:Name="ItemsHost" />
                        </StackPanel>
                        <ControlTemplate.Triggers>
                            <Trigger Property="IsExpanded" Value="false">
                                <Setter TargetName="ItemsHost" Property="Visibility" Value="Collapsed"/>
                            </Trigger>
                            <Trigger Property="HasItems" Value="false">
                                <Setter TargetName="Expander" Property="Visibility" Value="Hidden"/>
                            </Trigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="HasHeader" Value="false"/>
                                    <Condition Property="Width" Value="Auto"/>
                                </MultiTrigger.Conditions>
                                <Setter TargetName="PART_Header" Property="MinWidth" Value="75"/>
                            </MultiTrigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="HasHeader" Value="false"/>
                                    <Condition Property="Height" Value="Auto"/>
                                </MultiTrigger.Conditions>
                                <Setter TargetName="PART_Header" Property="MinHeight" Value="19"/>
                            </MultiTrigger>
                            <Trigger Property="IsSelected" Value="true">
                                <!--<Setter TargetName="Bd" Property="Background" Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>-->
                                <Setter TargetName="Bd" Property="Background" Value="#FFF7D280"/>
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.HighlightTextBrushKey}}"/>
                            </Trigger>
                            <MultiTrigger>
                                <MultiTrigger.Conditions>
                                    <Condition Property="IsSelected" Value="true"/>
                                    <Condition Property="IsSelectionActive" Value="false"/>
                                </MultiTrigger.Conditions>
                                <!--<Setter TargetName="Bd" Property="Background" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>-->
                                <Setter TargetName="Bd" Property="Background" Value="#FFDADADA"/>
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
                            </MultiTrigger>
                            <Trigger Property="IsEnabled" Value="false">
                                <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                            </Trigger>
                        </ControlTemplate.Triggers>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
            <Style.Triggers>
                <!-- Selected and has focus -->
                <Trigger Property="IsSelected" Value="True">
                    <Setter Property="BorderBrush" Value="{StaticResource HT_Background_Orange}"/>
                </Trigger>
                <!-- Mouse over -->
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="Background" Value="#FFFDE8BA"/>
                    <!--<Setter Property="Background">
                        <Setter.Value>
                            <LinearGradientBrush EndPoint="0,1" StartPoint="0,0">
                                <GradientStop Color="#FFFAFBFD" Offset="0"/>
                                <GradientStop Color="#fadfa3" Offset="1"/>
                            </LinearGradientBrush>
                        </Setter.Value>
                    </Setter>-->
                    <Setter Property="BorderBrush" Value="#f59246"/>
                </Trigger>
                <!-- Selected but does not have the focus -->
                <MultiTrigger>
                    <MultiTrigger.Conditions>
                        <Condition Property="IsSelected" Value="True"/>
                        <Condition Property="IsSelectionActive" Value="False"/>
                    </MultiTrigger.Conditions>
                    <Setter Property="BorderBrush" Value="#f59246"/>
                </MultiTrigger>
            </Style.Triggers>
            <Style.Resources>
                <Style TargetType="Border">
                    <Setter Property="CornerRadius" Value="0"/>
                </Style>
            </Style.Resources>
        </Style>
    </TreeView.ItemContainerStyle>
    <TreeView.ItemTemplate>
        <HierarchicalDataTemplate DataType="{x:Type local:FileSystemObjectInfo}" ItemsSource="{Binding Path=Children}">
            <StackPanel Orientation="Horizontal">
                <Image
                    Source="{Binding Path=ImageSource, UpdateSourceTrigger=PropertyChanged}" 
                    Margin="0,1,8,1"
                    Height="24"
                    Width="24"/>
                <TextBlock
                    Text="{Binding Path=FileSystemInfo.Name}"
                    VerticalAlignment="Center"/>
            </StackPanel>
        </HierarchicalDataTemplate>
    </TreeView.ItemTemplate>
    <TreeView.Resources>

        <!-- Brushes for the selected item -->
        <LinearGradientBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" EndPoint="0,1" StartPoint="0,0">
            <GradientStop Color="#FFFDF2DA" Offset="0"/>
            <GradientStop Color="#FFF7D280" Offset="1"/>
        </LinearGradientBrush>
        <LinearGradientBrush x:Key="{x:Static SystemColors.ControlBrushKey}" EndPoint="0,1" StartPoint="0,0">
            <GradientStop Color="White" Offset="0"/>
            <GradientStop Color="#FFE2E2E2" Offset="1"/>
        </LinearGradientBrush>
        <SolidColorBrush x:Key="{x:Static SystemColors.HighlightTextBrushKey}" Color="Black" />
        <SolidColorBrush x:Key="{x:Static SystemColors.ControlTextBrushKey}" Color="Black" />
    </TreeView.Resources>
</TreeView>

public class LeftMarginMultiplierConverter : IValueConverter
{
    public double Length { get; set; }

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        TreeViewItem item = value as TreeViewItem;
        if (item == null)
            return new Thickness(0);

        return new Thickness(Length * item.GetDepth(), 0, 0, 0);
    }

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

public static class TreeViewItemExtensions
{
    public static int GetDepth(this TreeViewItem item)
    {
        TreeViewItem parent;
        while ((parent = GetParent(item)) != null)
        {
            return GetDepth(parent) + 1;
        }
        return 0;
    }

    private static TreeViewItem GetParent(TreeViewItem item)
    {
        DependencyObject parent = item != null ? VisualTreeHelper.GetParent(item) : null;
        while (parent != null && !(parent is TreeViewItem || parent is TreeView))
        {
            parent = VisualTreeHelper.GetParent(parent);
        }
        return parent as TreeViewItem;
    }
}

<Style x:Key="ExpandCollapseToggleStyle" TargetType="ToggleButton">
    <Setter Property="Focusable" Value="False"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="ToggleButton">
                <Grid
                Width="15"
                Height="13"
                Background="Transparent">
                    <Path 
                    x:Name="ExpandPath"
                    HorizontalAlignment="Left" 
                    VerticalAlignment="Center" 
                    Margin="1,1,1,1"
                    Fill="{StaticResource GlyphBrush}"
                    Data="M 4 0 L 8 4 L 4 8 Z"/>
                </Grid>
                <ControlTemplate.Triggers>
                    <Trigger Property="IsChecked" Value="True">
                        <Setter Property="Data" TargetName="ExpandPath" Value="M 0 4 L 8 4 L 4 8 Z"/>
                    </Trigger>
                </ControlTemplate.Triggers>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

If you have any questions, let me know!

Regards

Question 3

Completing Dominic Jonas's solution, using GetChildOfType method from How to get children of a WPF container by type?:

public class LeftMarginMultiplierConverter : IValueConverter
    {
        public int Length { get; set; }
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            Thickness thickness = new Thickness(0, 0, 0, 0);
            if (value != null)
            {
                TreeViewItem treeViewItem = (TreeViewItem)value;
                ItemsControl parent = ItemsControl.ItemsControlFromItemContainer(treeViewItem);
                if (parent != null)
                {
                    if (parent.GetType() == typeof(TreeView))
                    {
                        thickness = new Thickness(System.Convert.ToDouble(Length), 5, 5, 5);
                    }
                    else if (parent.GetType() == typeof(TreeViewItem))
                    {
                        Grid grid = (Grid) Helper.GetChildOfType<Grid>(parent);
                        if(grid != null)
                            thickness = new Thickness(System.Convert.ToDouble(grid.Margin.Left + Length), 5, 5, 5);
                    }
                }
            }
            return thickness;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
    public static class Helper
    {
        public static T GetChildOfType<T>(this DependencyObject depObj) where T : DependencyObject
        {
            if (depObj == null) return null;

            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(depObj); i++)
            {
                var child = VisualTreeHelper.GetChild(depObj, i);

                var result = (child as T) ?? GetChildOfType<T>(child);
                if (result != null) return result;
            }
            return null;
        }
    }

And Highlight mouse over in only single row: How can I make WPF Trigger for IsMouseOver on TreeViewItem NOT affect all parents of the moused-over control?