I’ve been an asp.net developer for some time now and I was excited to jump on to Silverlight when it 2.0
was released a few months ago.  One thing I really struggled with was applying conditional formatting to
the individual cells in the DataGrid control.  Coming from an asp.net background, I carried a lot of
assumptions with me (big mistake).  I thought I could get a hold of the rows or cells collection and have
my way with it, but no such luck.  I stumbled down several paths which all ultimately lead to dead ends. 
After killing hours (maybe days) on trying to figure this out, I had to let it go and move on.  Now a month
later I decided to give it another shot and I finally got it.  The answer was right in front of me all along. 
I knew about the IValueConverter interface, but I didn’t fully understand its capabilities.  I thought it was
only used for converting an object into a text representation or vice versa.  Actually, you can return
anything you want from it.  So you can return a Button, Grid, or whatever.

Another aspect I couldn’t figure out was how to get access to page members from within the Convert
method.  For example, I wanted to render a button in the cell and wire up the button’s click event to a
method in the page.  Sure, you could do this to a certain extent using templates, but then I couldn’t
find a way to change the template conditionally based on a value in the bound data item.

The solution I came up with was to create a delegate along with a class which implemented the
IValueConverter interface and exposed two events.  One for converting and the other for converting
back.  I can then declare this converter in the resources collection and setup a handler in the page
as shown below.

<UserControl.Resources>
    <local:UniversalConverter x:Key="ageConverter" Converting="ConvertAge" />
    <local:UniversalConverter x:Key="nameConverter" Converting="ConvertName" />
</UserControl.Resources>

Here is the markup i used in the “First Name” column of the DataGrid.

<data:DataGridTemplateColumn Header="First Name">
    <data:DataGridTemplateColumn.CellTemplate>
        <DataTemplate>
            <ContentControl Content="{Binding Converter={StaticResource nameConverter}}"
                HorizontalContentAlignment="Stretch"  
                VerticalContentAlignment="Stretch" />
        </DataTemplate>
    </data:DataGridTemplateColumn.CellTemplate>
</data:DataGridTemplateColumn>

Here is the “ConvertName” method I wired up from the converter defined in the resources collection.

   1:  private object ConvertName(object value, Type targetType, 
                      object parameter, CultureInfo culture) {

   2:      Employee employee = value as Employee;

   3:      if (employee == null) {

   4:          return value;

   5:      }

   6:   

   7:      if (employee.FirstName.Contains('a')) {

   8:          Button btn = new Button();

   9:          btn.Content = employee.FirstName;

  10:          btn.Click += ((sender, e) => {

  11:            HtmlPage.Window.Alert(

  12:              string.Format(
                   "There is a button here because \"{0}\" contains an \"a\".", 

  13:              employee.FirstName));

  14:          });

  15:   

  16:          return btn;

  17:      }

  18:      return new TextBlock {Text = employee.FirstName};

  19:  }

This is the IConverter class and delegate I created to handle the conversions.

   1:  public class UniversalConverter : IValueConverter {

   2:   

   3:      public object Convert(object value, Type targetType, 
                         object parameter, CultureInfo culture) {

   4:          return this.OnConverting(value, targetType, 
                                        parameter, culture);

   5:      }

   6:   

   7:      public object ConvertBack(object value, Type targetType, 
                         object parameter, CultureInfo culture) {

   8:          return this.OnConvertingBack(value, targetType, 
                                            parameter, culture);

   9:      }

  10:   

  11:      protected object OnConverting(object value, Type targetType, 
                            object parameter, CultureInfo culture) {

  12:          UniversalConverterHandler handler = this.Converting;

  13:          if (handler != null) {

  14:              return handler(value, targetType, parameter, culture);

  15:          }

  16:          return value;

  17:      }

  18:   

  19:      protected object OnConvertingBack(object value, Type targetType, 
                            object parameter, CultureInfo culture) {

  20:          UniversalConverterHandler handler = this.ConvertingBack;

  21:          if (handler != null) {

  22:              return handler(value, targetType, parameter, culture);

  23:          }

  24:          return value;

  25:      }

  26:   

  27:      public event UniversalConverterHandler Converting;

  28:   

  29:      public event UniversalConverterHandler ConvertingBack;

  30:   

  31:  }

  32:   

  33:  public delegate object UniversalConverterHandler(object value, Type targetType, 
                              object parameter, CultureInfo culture);

And finally, here is a screenshot of the DataGrid. (Ugly, I know, but it proves my point.)

Here is a link to the complete solution.

I hope you find this useful and I look forward to hearing feedback and suggestions. 
Most importantly, let me know if you know of a better way to do this.

Thanks
-Joe