隐藏silverlight数据网格中的超链接按钮

Question

在我的tool.xaml中使用以下代码，我得到以下datagrid

<slData:DataGrid x:Name="Customer" ItemsSource="{Binding ReturnedItemAttributes}" AutoGenerateColumns="False"  HeadersVisibility="None" ScrollViewer.HorizontalScrollBarVisibility="Visible" ScrollViewer.VerticalScrollBarVisibility="Visible" MaxHeight="350" MaxWidth="350">

                    <slData:DataGrid.Resources>
                        <ResourceDictionary>
                            <local:HTTPVisibilityConverter x:Key="httpVisibility"/>
                            <local:VisibilityData x:Key="visibilityValue"/>
                        </ResourceDictionary>
                    </slData:DataGrid.Resources>
                    <slData:DataGrid.Columns>
                        <local:ExtendedDataGridTextColumn Binding="{Binding Path=Key}" FontWeight="Bold"/>                                
                        <local:ExtendedDataGridTextColumn Binding="{Binding Path=Value}" MyVisibility="{Binding Visible, Source={StaticResource visibilityValue}, Converter={StaticResource httpVisibility}, ConverterParameter=Reverse}"/>

                        <local:CustomDataGridTemplateColumn Width="40"  VisibilityBinding="{Binding Visible, Source={StaticResource visibilityValue}, Converter={StaticResource httpVisibility}}">
                            <local:CustomDataGridTemplateColumn.CellTemplate>
                            <DataTemplate>
                                    <HyperlinkButton Content="Pdf Link" Height="23" Name="PdfUrl" Width="76" NavigateUri="{Binding Path=Value, Mode=TwoWay}"    TargetName="_blank" Margin="5,10,10,7" Foreground="Blue" />
                                </DataTemplate>
                            </local:CustomDataGridTemplateColumn.CellTemplate>
                        </local:CustomDataGridTemplateColumn>

                    </slData:DataGrid.Columns>
                </slData:DataGrid>

上面的代码创建了一个datagrid，如下所示。请忽略column1 column2和column3标头。人们只是回答我的问题：

Column1  column2  Column3
    name    John     pdf
    CustomerID   1234   pdf
    Customer_url  http://www.test.com  pdf

我现在只想为customer_url显示cloumn3中的pdf超链接 为所有其他行划行和隐藏。我怎么能实现它。这是MVVM设计模式。以下是我希望数据网格显示的方式：

 Column1  column2  Column3
     name    John     
    CustomerID   1234    
 Customer_url  http://www.test.com  pdf

我的值转换器代码如下：

  public class HTTPVisibilityConverter : IValueConverter
 {
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        bool boolVisbility = (value != null) && value.ToString().StartsWith("http");

        boolVisbility = (parameter != null) ? !boolVisbility : boolVisbility;

        return boolVisbility ? Visibility.Visible : Visibility.Collapsed;
    }

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