WPF DataGrid How to bold only first row

Question

i'm using a Datagrid in WPF to populate some data. Once i have the data ready for display, i also need the first row, and only the first row to be bold. How can i achieve this?

Preferably i only want to modify my XAML. Worst case, i can make code changes on view-model (MVVM) side. But under no circumstance i am allowed to change the code-behind (ie: the view, so i cant give my DataGrid a x:Name and modify it from the view)

Please note datagrid may or may NOT be populated, so it cannot stop working if we attempt to bold a row that doesn't exist.

Thanks so much. Joe

Answer 1

A simple solution would be to implement a IMultiValueConverter which checks the row index. You would use the DataGrid.CellStyle to apply the converter:

CellFontWeightMultiValueConverter.cs

class CellFontWeightMultiValueConverter : IMultiValueConverter
{
  #region Implementation of IMultiValueConverter

  public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture) =>
    values[0] is MyDataModel item 
    && values[1] is IEnumerable<MyDataModel> items 
    && items.ToList().IndexOf(item) == 0
      ? FontWeights.ExtraBold
      : FontWeights.Normal;

  public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture) =>
    throw new NotSupportedException();

  #endregion
}

MainWindow.xaml

<Window>
  <DataGrid ItemsSource="{Binding MyDataModels}">
    <DataGrid.CellStyle>
      <Style TargetType="DataGridCell">
        <Setter Property="FontWeight">
          <Setter.Value>
            <MultiBinding Converter="{StaticResource CellForegroundMultiValueConverter}">
              <Binding />
              <Binding RelativeSource="{RelativeSource AncestorType=DataGrid}" 
                       Path="DataContext.MyDataModels" />
            </MultiBinding>
          </Setter.Value>
        </Setter>
      </Style>
    </DataGrid.CellStyle>
  </DataGrid>
</Window>