WPF TreeViewItem Style

Question

I am stuck on a very basic problem. I have a Treeview and I want the TreevieeItems to have a custom style.

For Example I want to change the height and set the background to a gradient.

I read something about ControlTemplates but I couldn't find any usefull resources.

EDIT

Thats what I have so far

<Style x:Key="myTreeViewItemStyle" TargetType="TreeViewItem">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type TreeViewItem}">

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

Answer 1

Here is the complete template from MSDN

    <!--=================================================================
      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>
    <Style x:Key="TreeViewItemFocusVisual">
      <Setter Property="Control.Template">
        <Setter.Value>
          <ControlTemplate>
            <Border>
              <Rectangle Margin="0,0,0,0"
                 StrokeThickness="5"
                 Stroke="Black"
                 StrokeDashArray="1 2"
                 Opacity="0"/>
           </Border>
         </ControlTemplate>
       </Setter.Value>
     </Setter>
   </Style>
   <Style x:Key="{x:Type TreeViewItem}"
     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}"
                  IsChecked="{Binding Path=IsExpanded,
                              RelativeSource={RelativeSource TemplatedParent}}"
                  ClickMode="Press"/>
          <Border Name="Bd"
              Grid.Column="1"
              Background="{TemplateBinding Background}"
              BorderBrush="{TemplateBinding BorderBrush}"
              BorderThickness="{TemplateBinding BorderThickness}"
              Padding="{TemplateBinding Padding}">
            <ContentPresenter x:Name="PART_Header"
                      ContentSource="Header"
                      HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"/>
          </Border>
          <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>
          <Trigger Property="IsSelected"
               Value="true">
            <Setter TargetName="Bd"
                Property="Background"
                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 TargetName="Bd"
                Property="Background"
                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>

EDIT:

I am stuck on a very basic problem. I have a Treeview and I want the TreevieeItems to have a custom style.

Check the above example, that's a custom style.

For Example I want to change the height and set the background to a gradient.

Change the property in the style to a gradient:

<Style TargetType="{x:Type TreeViewItem}">
        <Setter Property="Background" >
            <Setter.Value>
                <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                    <GradientStop Color="Black" Offset="0"/>
                    <GradientStop Color="White" Offset="1"/>
                </LinearGradientBrush>
            </Setter.Value>
        </Setter>
    </Style>

I read something about ControlTemplates but I couldn't find any usefull resources.

You can find most of controltemplates at MSDN or just by googling them.