WPF datagrid tooltip for hidden text

c#part

 public class TrimmedTextBlockVisibilityConverter : IValueConverter
    {

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (value == null) return Visibility.Collapsed;

            FrameworkElement textBlock = (FrameworkElement)value;

            textBlock.Measure(new System.Windows.Size(Double.PositiveInfinity, Double.PositiveInfinity));

            if (((FrameworkElement)value).ActualWidth < ((FrameworkElement)value).DesiredSize.Width)
                return Visibility.Visible;
            else
                return Visibility.Collapsed;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

xamlpart

    <DataGrid.Resources>
                <Style TargetType="{x:Type DataGridCell}">
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="{x:Type DataGridCell}">
                                <TextBlock Text="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Content.Text}" TextTrimming="CharacterEllipsis">
                                    <TextBlock.ToolTip>
                                        <ToolTip Visibility="{Binding RelativeSource={RelativeSource Self}, Path=PlacementTarget, Converter={StaticResource TrimToVisConverter}}">
                                            <ToolTip.Content>
                                                <TextBlock Text="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Content.Text}"/>
                                            </ToolTip.Content>
                                        </ToolTip>
                                    </TextBlock.ToolTip>
                 </TextBlock>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </DataGrid.Resources>