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c#wpftemplatescontroltemplateexpander

Why doesn't my Expander expand when I set its template?


I'm trying to change the colour of an Expander's expand button, and it seems the only way to do that is to change its control template, as there is no property to set that.

So, I've used Show Me The Template to grab the template for the Aero theme. I've then set that template on my Expander, with no other changes. It looks fine, but clicking on the button no longer causes it to expand.

Can anybody explain why this is happening? I expect it is something simple, but I'm still learning WPF and haven't been able to figure it out. Thank you.

Here is the complete code:

<Expander Header="Test">
  <Expander.Template>
    <ControlTemplate TargetType="Expander" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:s="clr-namespace:System;assembly=mscorlib" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
      <Border BorderThickness="{TemplateBinding Border.BorderThickness}" CornerRadius="3,3,3,3" BorderBrush="{TemplateBinding Border.BorderBrush}" Background="{TemplateBinding Panel.Background}" SnapsToDevicePixels="True">
        <DockPanel>
          <ToggleButton IsChecked="False" Content="{TemplateBinding HeaderedContentControl.Header}" ContentTemplate="{TemplateBinding HeaderedContentControl.HeaderTemplate}" Foreground="{TemplateBinding TextElement.Foreground}" FontFamily="{TemplateBinding TextElement.FontFamily}" FontSize="{TemplateBinding TextElement.FontSize}" FontStretch="{TemplateBinding TextElement.FontStretch}" FontStyle="{TemplateBinding TextElement.FontStyle}" FontWeight="{TemplateBinding TextElement.FontWeight}" HorizontalContentAlignment="{TemplateBinding Control.HorizontalContentAlignment}" VerticalContentAlignment="{TemplateBinding Control.VerticalContentAlignment}" Padding="{TemplateBinding Control.Padding}" Name="HeaderSite" MinWidth="0" MinHeight="0" Margin="1,1,1,1" DockPanel.Dock="Top">
            <ToggleButton.Style>
              <Style TargetType="ToggleButton">
                <Style.Resources>
                  <ResourceDictionary />
                </Style.Resources>
                <Setter Property="Control.Template">
                  <Setter.Value>
                    <ControlTemplate TargetType="ToggleButton">
                      <Border Padding="{TemplateBinding Control.Padding}">
                        <Grid Background="#00FFFFFF" SnapsToDevicePixels="False">
                          <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="19" />
                            <ColumnDefinition Width="*" />
                          </Grid.ColumnDefinitions>
                          <Ellipse Stroke="#FFA9A9A9" Name="circle" Width="19" Height="19" HorizontalAlignment="Center" VerticalAlignment="Center" />
                          <Path Data="M1,1.5L4.5,5 8,1.5" Stroke="#FF666666" StrokeThickness="2" Name="arrow" HorizontalAlignment="Center" VerticalAlignment="Center" SnapsToDevicePixels="False" />
                          <ContentPresenter RecognizesAccessKey="True" Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" Margin="4,0,0,0" HorizontalAlignment="Left" VerticalAlignment="Center" SnapsToDevicePixels="True" Grid.Column="1" />
                        </Grid>
                      </Border>
                      <ControlTemplate.Triggers>
                        <Trigger Property="ToggleButton.IsChecked">
                          <Setter TargetName="arrow" Property="Path.Data">
                            <Setter.Value>
                              <StreamGeometry>M1,4.5L4.5,1 8,4.5</StreamGeometry>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                        <Trigger Property="UIElement.IsMouseOver">
                          <Setter TargetName="circle" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF3C7FB1</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="arrow" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF222222</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                        <Trigger Property="ButtonBase.IsPressed">
                          <Setter TargetName="circle" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF526C7B</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="circle" Property="Shape.StrokeThickness">
                            <Setter.Value>
                              <s:Double>1.5</s:Double>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="arrow" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF003366</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                      </ControlTemplate.Triggers>
                    </ControlTemplate>
                  </Setter.Value>
                </Setter>
              </Style>
            </ToggleButton.Style>
            <ToggleButton.FocusVisualStyle>
              <Style TargetType="IFrameworkInputElement">
                <Style.Resources>
                  <ResourceDictionary />
                </Style.Resources>
                <Setter Property="Control.Template">
                  <Setter.Value>
                    <ControlTemplate>
                      <Border>
                        <Rectangle Stroke="#FF000000" StrokeThickness="1" StrokeDashArray="1 2" Margin="0,0,0,0" SnapsToDevicePixels="True" />
                      </Border>
                    </ControlTemplate>
                  </Setter.Value>
                </Setter>
              </Style>
            </ToggleButton.FocusVisualStyle>
          </ToggleButton>
          <ContentPresenter Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" Name="ExpandSite" Margin="{TemplateBinding Control.Padding}" HorizontalAlignment="{TemplateBinding Control.HorizontalContentAlignment}" VerticalAlignment="{TemplateBinding Control.VerticalContentAlignment}" Visibility="Collapsed" Focusable="False" DockPanel.Dock="Bottom" />
        </DockPanel>
      </Border>
      <ControlTemplate.Triggers>
        <Trigger Property="Expander.IsExpanded">
          <Setter TargetName="ExpandSite" Property="UIElement.Visibility" Value="{x:Static Visibility.Visible}" />
          <Trigger.Value>
            <s:Boolean>True</s:Boolean>
          </Trigger.Value>
        </Trigger>
        <Trigger Property="Expander.ExpandDirection">
          <Setter TargetName="ExpandSite" Property="DockPanel.Dock" Value="{x:Static Dock.Right}" />
          <Setter TargetName="HeaderSite" Property="DockPanel.Dock" Value="{x:Static Dock.Left}" />
          <Setter TargetName="HeaderSite" Property="FrameworkElement.Style">
            <Setter.Value>
              <Style TargetType="ToggleButton">
                <Style.Resources>
                  <ResourceDictionary />
                </Style.Resources>
                <Setter Property="Control.Template">
                  <Setter.Value>
                    <ControlTemplate TargetType="ToggleButton">
                      <Border Padding="{TemplateBinding Control.Padding}">
                        <Grid Background="#00FFFFFF" SnapsToDevicePixels="False">
                          <Grid.RowDefinitions>
                            <RowDefinition Height="19" />
                            <RowDefinition Height="*" />
                          </Grid.RowDefinitions>
                          <Grid>
                            <Grid.LayoutTransform>
                              <TransformGroup>
                                <TransformGroup.Children>
                                  <RotateTransform Angle="-90" />
                                </TransformGroup.Children>
                              </TransformGroup>
                            </Grid.LayoutTransform>
                            <Ellipse Stroke="#FFA9A9A9" Name="circle" Width="19" Height="19" HorizontalAlignment="Center" VerticalAlignment="Center" />
                            <Path Data="M1,1.5L4.5,5 8,1.5" Stroke="#FF666666" StrokeThickness="2" Name="arrow" HorizontalAlignment="Center" VerticalAlignment="Center" SnapsToDevicePixels="False" />
                          </Grid>
                          <ContentPresenter RecognizesAccessKey="True" Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" Margin="0,4,0,0" HorizontalAlignment="Center" VerticalAlignment="Top" SnapsToDevicePixels="True" Grid.Row="1" />
                        </Grid>
                      </Border>
                      <ControlTemplate.Triggers>
                        <Trigger Property="ToggleButton.IsChecked">
                          <Setter TargetName="arrow" Property="Path.Data">
                            <Setter.Value>
                              <StreamGeometry>M1,4.5L4.5,1 8,4.5</StreamGeometry>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                        <Trigger Property="UIElement.IsMouseOver">
                          <Setter TargetName="circle" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF3C7FB1</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="arrow" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF222222</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                        <Trigger Property="ButtonBase.IsPressed">
                          <Setter TargetName="circle" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF526C7B</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="circle" Property="Shape.StrokeThickness">
                            <Setter.Value>
                              <s:Double>1.5</s:Double>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="arrow" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF003366</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                      </ControlTemplate.Triggers>
                    </ControlTemplate>
                  </Setter.Value>
                </Setter>
              </Style>
            </Setter.Value>
          </Setter>
          <Trigger.Value>
            <x:Static Member="ExpandDirection.Right" />
          </Trigger.Value>
        </Trigger>
        <Trigger Property="Expander.ExpandDirection">
          <Setter TargetName="ExpandSite" Property="DockPanel.Dock" Value="{x:Static Dock.Top}" />
          <Setter TargetName="HeaderSite" Property="DockPanel.Dock" Value="{x:Static Dock.Bottom}" />
          <Setter TargetName="HeaderSite" Property="FrameworkElement.Style">
            <Setter.Value>
              <Style TargetType="ToggleButton">
                <Style.Resources>
                  <ResourceDictionary />
                </Style.Resources>
                <Setter Property="Control.Template">
                  <Setter.Value>
                    <ControlTemplate TargetType="ToggleButton">
                      <Border Padding="{TemplateBinding Control.Padding}">
                        <Grid Background="#00FFFFFF" SnapsToDevicePixels="False">
                          <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="19" />
                            <ColumnDefinition Width="*" />
                          </Grid.ColumnDefinitions>
                          <Grid>
                            <Grid.LayoutTransform>
                              <TransformGroup>
                                <TransformGroup.Children>
                                  <RotateTransform Angle="180" />
                                </TransformGroup.Children>
                              </TransformGroup>
                            </Grid.LayoutTransform>
                            <Ellipse Stroke="#FFA9A9A9" Name="circle" Width="19" Height="19" HorizontalAlignment="Center" VerticalAlignment="Center" />
                            <Path Data="M1,1.5L4.5,5 8,1.5" Stroke="#FF666666" StrokeThickness="2" Name="arrow" HorizontalAlignment="Center" VerticalAlignment="Center" SnapsToDevicePixels="False" />
                          </Grid>
                          <ContentPresenter RecognizesAccessKey="True" Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" Margin="4,0,0,0" HorizontalAlignment="Left" VerticalAlignment="Center" SnapsToDevicePixels="True" Grid.Column="1" />
                        </Grid>
                      </Border>
                      <ControlTemplate.Triggers>
                        <Trigger Property="ToggleButton.IsChecked">
                          <Setter TargetName="arrow" Property="Path.Data">
                            <Setter.Value>
                              <StreamGeometry>M1,4.5L4.5,1 8,4.5</StreamGeometry>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                        <Trigger Property="UIElement.IsMouseOver">
                          <Setter TargetName="circle" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF3C7FB1</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="arrow" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF222222</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                        <Trigger Property="ButtonBase.IsPressed">
                          <Setter TargetName="circle" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF526C7B</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="circle" Property="Shape.StrokeThickness">
                            <Setter.Value>
                              <s:Double>1.5</s:Double>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="arrow" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF003366</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                      </ControlTemplate.Triggers>
                    </ControlTemplate>
                  </Setter.Value>
                </Setter>
              </Style>
            </Setter.Value>
          </Setter>
          <Trigger.Value>
            <x:Static Member="ExpandDirection.Up" />
          </Trigger.Value>
        </Trigger>
        <Trigger Property="Expander.ExpandDirection">
          <Setter TargetName="ExpandSite" Property="DockPanel.Dock" Value="{x:Static Dock.Left}" />
          <Setter TargetName="HeaderSite" Property="DockPanel.Dock" Value="{x:Static Dock.Right}" />
          <Setter TargetName="HeaderSite" Property="FrameworkElement.Style">
            <Setter.Value>
              <Style TargetType="ToggleButton">
                <Style.Resources>
                  <ResourceDictionary />
                </Style.Resources>
                <Setter Property="Control.Template">
                  <Setter.Value>
                    <ControlTemplate TargetType="ToggleButton">
                      <Border Padding="{TemplateBinding Control.Padding}">
                        <Grid Background="#00FFFFFF" SnapsToDevicePixels="False">
                          <Grid.RowDefinitions>
                            <RowDefinition Height="19" />
                            <RowDefinition Height="*" />
                          </Grid.RowDefinitions>
                          <Grid>
                            <Grid.LayoutTransform>
                              <TransformGroup>
                                <TransformGroup.Children>
                                  <RotateTransform Angle="90" />
                                </TransformGroup.Children>
                              </TransformGroup>
                            </Grid.LayoutTransform>
                            <Ellipse Stroke="#FFA9A9A9" Name="circle" Width="19" Height="19" HorizontalAlignment="Center" VerticalAlignment="Center" />
                            <Path Data="M1,1.5L4.5,5 8,1.5" Stroke="#FF666666" StrokeThickness="2" Name="arrow" HorizontalAlignment="Center" VerticalAlignment="Center" SnapsToDevicePixels="False" />
                          </Grid>
                          <ContentPresenter RecognizesAccessKey="True" Content="{TemplateBinding ContentControl.Content}" ContentTemplate="{TemplateBinding ContentControl.ContentTemplate}" ContentStringFormat="{TemplateBinding ContentControl.ContentStringFormat}" Margin="0,4,0,0" HorizontalAlignment="Center" VerticalAlignment="Top" SnapsToDevicePixels="True" Grid.Row="1" />
                        </Grid>
                      </Border>
                      <ControlTemplate.Triggers>
                        <Trigger Property="ToggleButton.IsChecked">
                          <Setter TargetName="arrow" Property="Path.Data">
                            <Setter.Value>
                              <StreamGeometry>M1,4.5L4.5,1 8,4.5</StreamGeometry>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                        <Trigger Property="UIElement.IsMouseOver">
                          <Setter TargetName="circle" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF3C7FB1</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="arrow" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF222222</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                        <Trigger Property="ButtonBase.IsPressed">
                          <Setter TargetName="circle" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF526C7B</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="circle" Property="Shape.StrokeThickness">
                            <Setter.Value>
                              <s:Double>1.5</s:Double>
                            </Setter.Value>
                          </Setter>
                          <Setter TargetName="arrow" Property="Shape.Stroke">
                            <Setter.Value>
                              <SolidColorBrush>#FF003366</SolidColorBrush>
                            </Setter.Value>
                          </Setter>
                          <Trigger.Value>
                            <s:Boolean>True</s:Boolean>
                          </Trigger.Value>
                        </Trigger>
                      </ControlTemplate.Triggers>
                    </ControlTemplate>
                  </Setter.Value>
                </Setter>
              </Style>
            </Setter.Value>
          </Setter>
          <Trigger.Value>
            <x:Static Member="ExpandDirection.Left" />
          </Trigger.Value>
        </Trigger>
        <Trigger Property="UIElement.IsEnabled">
          <Setter Property="TextElement.Foreground">
            <Setter.Value>
              <DynamicResource ResourceKey="{x:Static SystemColors.GrayTextBrushKey}" />
            </Setter.Value>
          </Setter>
          <Trigger.Value>
            <s:Boolean>False</s:Boolean>
          </Trigger.Value>
        </Trigger>
      </ControlTemplate.Triggers>
    </ControlTemplate>
  </Expander.Template>
  Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</Expander>

Solution

  • When I edit a copy of the Expander template in Blend, which should do roughly the same thing as you are doing with ShowMeTheTemplate, the IsChecked property of the ToggleButton named HeaderSite is not False (as it is in your XAML above) but this expression:

    IsChecked="{Binding IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" 
    

    So the toggle state of the button is bound to the IsExpanded property of the control. That's the way the toggle button takes effect.