Binding custom dependency property to custom WPF style

Question

I have an issue when designing a inherited Expander. My intention is to have a progress bar behind the toggle button and text in the default Expander header.

I have this XAML code which gives me the progress bar in the header. It is a custom style.

<Style x:Key="CurrentScanExpanderStyle" TargetType="{x:Type local:ProgressExpander}">
        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
        <Setter Property="Background" Value="Transparent"/>
        <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
        <Setter Property="VerticalContentAlignment" Value="Stretch"/>
        <Setter Property="BorderBrush" Value="Transparent"/>
        <Setter Property="BorderThickness" Value="1"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:ProgressExpander}">
                    <Border SnapsToDevicePixels="true" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="3">
                        <DockPanel>
                            <Grid DockPanel.Dock="Top">
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="*"/>
                                </Grid.ColumnDefinitions>
                                <ProgressBar Name="ProgressBar"/>
                                <ToggleButton FontFamily="{TemplateBinding FontFamily}" FontSize="{TemplateBinding FontSize}" FontStretch="{TemplateBinding FontStretch}" FontStyle="{TemplateBinding FontStyle}" FontWeight="{TemplateBinding FontWeight}" Foreground="{TemplateBinding Foreground}" HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}" Padding="{TemplateBinding Padding}" VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}" FocusVisualStyle="{StaticResource ExpanderHeaderFocusVisual}" Margin="1" MinHeight="0" MinWidth="0" x:Name="HeaderSite" Style="{StaticResource ExpanderDownHeaderStyle}" IsChecked="{Binding Path=IsExpanded, Mode=TwoWay, RelativeSource={RelativeSource TemplatedParent}}" Content="{TemplateBinding Header}" ContentTemplate="{TemplateBinding HeaderTemplate}" ContentTemplateSelector="{TemplateBinding HeaderTemplateSelector}"/>
                            </Grid>
                            <ContentPresenter Focusable="false" Visibility="Collapsed" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" Margin="{TemplateBinding Padding}" x:Name="ExpandSite" VerticalAlignment="{TemplateBinding VerticalContentAlignment}" DockPanel.Dock="Bottom"/>
                        </DockPanel>
                    </Border>
                    <ControlTemplate.Triggers>
                        <!-- Triggers haven't changed from the default -->
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

this works fine but I am having trouble binding my custom dependency property which controls the progress percentage.

    public class ProgressExpander : Expander
{
    static ProgressExpander()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(ProgressExpander), new FrameworkPropertyMetadata(typeof(ProgressExpander)));
    }       



    public int Progress
    {
        get { return (int)GetValue(ProgressProperty); }
        set { SetValue(ProgressProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Progress.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty ProgressProperty =
        DependencyProperty.Register("Progress", typeof(int), typeof(ProgressExpander), new UIPropertyMetadata(0));


}

This is the code inside of the window:

            <local:ProgressExpander Grid.Row="1" Header="Current Scan" ExpandDirection="Down" x:Name="currentScanExpander" Style="{DynamicResource CurrentScanExpanderStyle}">
                <Canvas Background="SkyBlue" 
                        Name="currentScanCanvas"
                        Height="{Binding ElementName=currentScanExpander, Path=ActualWidth}"
                        />
            </local:ProgressExpander>

I'm not sure how to bind this dependency property progress to the progress value in the ProgressBar within the style.

Any help would be appreciated.

Answer 1

In the style, we can use a standard Binding with a RelativeSource to set up the property.

<ProgressBar Name="ProgressBar"
             Value="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Progress}"
             Minimum="0"
             Maximum="100" />

Then, in the window we just add Progress="50" or a binding to somewhere else.

You will also need to set the Button's background to transparent, or change some manner of the layout, in order to see it.