WPF: Custom +- in TreeView - wpf

Question

It's possible to change the built-in collapse-expand icons of TreeView control (+-) to my own icons?
Thanks in advance!

Answer 1

Unfortunately, you will need to retemplate the TreeViewItem to achieve that. This default style may help get you started. Note the paths that will need to be substituted for your images.
<Style x:Key="TreeViewItemFocusVisual">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<Rectangle/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="ExpandCollapseToggleStyle" TargetType="{x:Type ToggleButton}">
<Setter Property="Focusable" Value="False"/>
<Setter Property="Width" Value="19"/>
<Setter Property="Height" Value="13"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Border Width="19" Height="13" Background="Transparent">
<Border SnapsToDevicePixels="true" Width="9" Height="9"
BorderBrush="#FF7898B5" BorderThickness="1" CornerRadius="1">
<Border.Background>
<LinearGradientBrush EndPoint="1,1" StartPoint="0,0">
<GradientStop Color="White" Offset=".2"/>
<GradientStop Color="#FFC0B7A6" Offset="1"/>
</LinearGradientBrush>
</Border.Background>
<Path x:Name="ExpandPath"
Margin="1,1,1,1"
Fill="Black"
Data="M 0 2 L 0 3 L 2 3 L 2 5 L 3 5 L 3 3 L 5 3 L 5 2 L 3 2 L 3 0 L 2 0 L 2 2 Z"/>
</Border>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="True">
<Setter Property="Data" TargetName="ExpandPath"
Value="M 0 2 L 0 3 L 5 3 L 5 2 Z"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="TreeViewItemStyle1" TargetType="{x:Type TreeViewItem}">
<Setter Property="Background" Value="Transparent"/>
<Setter Property="HorizontalContentAlignment"
Value="{Binding Path=HorizontalContentAlignment,
RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
<Setter Property="VerticalContentAlignment"
Value="{Binding Path=VerticalContentAlignment,
RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}"/>
<Setter Property="Padding" Value="1,0,0,0"/>
<Setter Property="Foreground"
Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
<Setter Property="FocusVisualStyle" Value="{StaticResource TreeViewItemFocusVisual}"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TreeViewItem}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition MinWidth="19" Width="Auto"/>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition/>
</Grid.RowDefinitions>
<ToggleButton x:Name="Expander"
Style="{StaticResource ExpandCollapseToggleStyle}"
ClickMode="Press"
IsChecked="{Binding Path=IsExpanded,
RelativeSource={RelativeSource TemplatedParent}}"/>
<Border Grid.Column="1" x:Name="Bd"
SnapsToDevicePixels="true"
Background="{TemplateBinding Background}"
BorderBrush="{TemplateBinding BorderBrush}"
BorderThickness="{TemplateBinding BorderThickness}"
Padding="{TemplateBinding Padding}">
<ContentPresenter x:Name="PART_Header"
SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"
HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
ContentSource="Header"/>
</Border>
<ItemsPresenter x:Name="ItemsHost" Grid.Column="1" Grid.ColumnSpan="2" Grid.Row="1"/>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsExpanded" Value="false">
<Setter Property="Visibility" TargetName="ItemsHost" Value="Collapsed"/>
</Trigger>
<Trigger Property="HasItems" Value="false">
<Setter Property="Visibility" TargetName="Expander" Value="Hidden"/>
</Trigger>
<Trigger Property="IsSelected" Value="true">
<Setter Property="Background" TargetName="Bd"
Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
<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 Property="Background" TargetName="Bd"
Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>
<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>

Answer 2

Thank you very much, Kent!
Here is the solution for my case:
<Style x:Key="styleTreeViewExpandCollapse" TargetType="{x:Type ToggleButton}">
<Setter Property="OverridesDefaultStyle" Value="True"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ToggleButton}">
<Image x:Name="image" Source="images/img1.ico" />
<ControlTemplate.Triggers>
<Trigger Property="IsChecked" Value="true">
<Setter TargetName="image" Property="Source" Value="images/img2.ico" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style x:Key="styleTreeView" TargetType="{x:Type TreeViewItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TreeViewItem}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition MinWidth="19" Width="Auto"/>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition/>
</Grid.RowDefinitions>
<ToggleButton Grid.Column="0" x:Name="Expander"
Style="{StaticResource styleTreeViewExpandCollapse}"
IsChecked="{Binding Path=IsExpanded,
RelativeSource={RelativeSource TemplatedParent}}"
ClickMode="Press"
Width="16" Height="16"/>
<ContentPresenter Grid.Column="1" x:Name="PART_Header"
ContentSource="Header"
HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"/>
<ItemsPresenter x:Name="ItemsHost"
Grid.Row="1"
Grid.Column="1" Grid.ColumnSpan="2"/>
</Grid>
<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>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Icons img1.ico and img2.ico are an arrows.