I have edited the standard GroupBox template as I wanted to customize it. Apart from other customizations, I wanted the GroupBox header to be Horizantally aligned in the Center instead of Left or Right. The alignment of the Header is not a problem however, the real problem is the OpacityMask defined for the Border controls. The opacity mask sets the transparent space behind the groupbox header where the borders are not drawn. I haven't able to figure it out how to place the transparent space / gap behind the groupbox header when I set the header to the center.
Here is how my XAML looks like: (Please navigate to the section beginning with "Border.OpacityMask" which sets the transparent gap in the border around the header)
<ControlTemplate x:Key="GroupBoxControlTemplate1" TargetType="{x:Type GroupBox}">
<Grid SnapsToDevicePixels="True">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="6"/>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="6"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
<RowDefinition Height="6"/>
</Grid.RowDefinitions>
<Border Background="{TemplateBinding Background}" BorderBrush="Transparent"
BorderThickness="{TemplateBinding BorderThickness}"
CornerRadius="4" Grid.Column="1 " Grid.ColumnSpan="4"
Grid.Row="1" Grid.RowSpan="3" HorizontalAlignment="Stretch"/>
<Border x:Name="Header" Grid.Column="2" Grid.RowSpan="2" HorizontalAlignment="Left"
Padding="3,1,3,0" VerticalAlignment="Stretch">
<Border.Effect>
<DropShadowEffect BlurRadius="10" Direction="334"/>
</Border.Effect>
<ContentPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"
Content="{TemplateBinding Header}"
ContentSource="Header"
ContentStringFormat="{TemplateBinding HeaderStringFormat}"
ContentTemplate="{TemplateBinding HeaderTemplate}"
RecognizesAccessKey="True" Height="Auto"
VerticalAlignment="Center"
HorizontalAlignment="Center"
OpacityMask="#FF3844BD" Margin="0,1,0,0">
</ContentPresenter>
</Border>
<ContentPresenter Margin="{TemplateBinding Padding}"
SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"
Content="{TemplateBinding Content}"
ContentStringFormat="{TemplateBinding ContentStringFormat}"
ContentTemplate="{TemplateBinding ContentTemplate}"
Grid.Column="1" Grid.ColumnSpan="2" Grid.Row="2"/>
<Border BorderBrush="White" BorderThickness="{TemplateBinding BorderThickness}"
CornerRadius="4" Grid.ColumnSpan="3" Grid.Row="1" Grid.RowSpan="3" RenderTransformOrigin="0.5,0.5" Margin="0">
<Border.OpacityMask>
<MultiBinding ConverterParameter="7" UpdateSourceTrigger="Default">
<MultiBinding.Converter>
<BorderGapMaskConverter/>
</MultiBinding.Converter>
<Binding Path="ActualWidth" ElementName="Header"/>
<Binding Path="ActualWidth" RelativeSource="{RelativeSource Self}"/>
<Binding Path="ActualHeight" RelativeSource="{RelativeSource Self}"/>
</MultiBinding>
</Border.OpacityMask>
<Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="4">
<Border BorderBrush="White" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="4"/>
</Border>
</Border>
</Grid>
Many thanks for your help in advance.
-Wajahat
I had to do something similar some time ago, I wanted to create a GroupBox with two headers (one on the left and one on the right). I just used Reflector to get the code for BorderGapMaskConverter, and modified it to create my own converter. You could probably do the same here.
EDIT: I modified my converter to make it work for a centered header.
Here's the ControlTemplate
<ControlTemplate TargetType="{x:Type GroupBox}">
<Grid SnapsToDevicePixels="true">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="6"/>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="6"/>
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
<RowDefinition Height="6"/>
</Grid.RowDefinitions>
<Border CornerRadius="4"
Grid.Row="1"
Grid.RowSpan="3"
Grid.Column="0"
Grid.ColumnSpan="5"
BorderThickness="{TemplateBinding BorderThickness}"
BorderBrush="Transparent"
Background="{TemplateBinding Background}"/>
<Border x:Name="Header"
Padding="3,1,3,0"
Grid.Row="0"
Grid.RowSpan="2"
Grid.Column="2">
<ContentPresenter ContentSource="Header"
RecognizesAccessKey="True"
SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
</Border>
<ContentPresenter Grid.Row="2"
Grid.Column="1"
Grid.ColumnSpan="3"
Margin="{TemplateBinding Padding}"
SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
<Border CornerRadius="4"
Grid.Row="1"
Grid.RowSpan="3"
Grid.ColumnSpan="5"
BorderThickness="{TemplateBinding BorderThickness}"
BorderBrush="White">
<Border.OpacityMask>
<MultiBinding Converter="{StaticResource CenterBorderGapMaskConverter}">
<Binding ElementName="Header"
Path="ActualWidth"/>
<Binding RelativeSource="{RelativeSource Self}"
Path="ActualWidth"/>
<Binding RelativeSource="{RelativeSource Self}"
Path="ActualHeight"/>
</MultiBinding>
</Border.OpacityMask>
<Border BorderThickness="{TemplateBinding BorderThickness}"
BorderBrush="{TemplateBinding BorderBrush}"
CornerRadius="3">
<Border BorderThickness="{TemplateBinding BorderThickness}"
BorderBrush="White"
CornerRadius="2"/>
</Border>
</Border>
</Grid>
</ControlTemplate>
And here's the converter:
class CenterBorderGapMaskConverter : IMultiValueConverter
{
// Methods
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
Type type = typeof(double);
if (values == null
|| values.Length != 3
|| values[0] == null
|| values[1] == null
|| values[2] == null
|| !type.IsAssignableFrom(values[0].GetType())
|| !type.IsAssignableFrom(values[1].GetType())
|| !type.IsAssignableFrom(values[2].GetType()))
{
return DependencyProperty.UnsetValue;
}
double pixels = (double)values[0];
double width = (double)values[1];
double height = (double)values[2];
if ((width == 0.0) || (height == 0.0))
{
return null;
}
Grid visual = new Grid();
visual.Width = width;
visual.Height = height;
ColumnDefinition colDefinition1 = new ColumnDefinition();
ColumnDefinition colDefinition2 = new ColumnDefinition();
ColumnDefinition colDefinition3 = new ColumnDefinition();
colDefinition1.Width = new GridLength(1.0, GridUnitType.Star);
colDefinition2.Width = new GridLength(pixels);
colDefinition3.Width = new GridLength(1.0, GridUnitType.Star);
visual.ColumnDefinitions.Add(colDefinition1);
visual.ColumnDefinitions.Add(colDefinition2);
visual.ColumnDefinitions.Add(colDefinition3);
RowDefinition rowDefinition1 = new RowDefinition();
RowDefinition rowDefinition2 = new RowDefinition();
rowDefinition1.Height = new GridLength(height / 2.0);
rowDefinition2.Height = new GridLength(1.0, GridUnitType.Star);
visual.RowDefinitions.Add(rowDefinition1);
visual.RowDefinitions.Add(rowDefinition2);
Rectangle rectangle1 = new Rectangle();
Rectangle rectangle2 = new Rectangle();
Rectangle rectangle3 = new Rectangle();
rectangle1.Fill = Brushes.Black;
rectangle2.Fill = Brushes.Black;
rectangle3.Fill = Brushes.Black;
Grid.SetRowSpan(rectangle1, 2);
Grid.SetRow(rectangle1, 0);
Grid.SetColumn(rectangle1, 0);
Grid.SetRow(rectangle2, 1);
Grid.SetColumn(rectangle2, 1);
Grid.SetRowSpan(rectangle3, 2);
Grid.SetRow(rectangle3, 0);
Grid.SetColumn(rectangle3, 2);
visual.Children.Add(rectangle1);
visual.Children.Add(rectangle2);
visual.Children.Add(rectangle3);
return new VisualBrush(visual);
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
{
return new object[] { Binding.DoNothing };
}
}
来源：https://stackoverflow.com/questions/4235252/wpf-groupbox-header-customization