Question

I have a column defined like this:

<DataGridTextColumn Binding="{Binding Path=FileSizeBytes, Mode=OneWay}" Header="Size" IsReadOnly="True" />

But instead of displaying the file size as a big number, I’d like to display units, but still have it sort by the actual FileSizeBytes. Is there some way I can run it through a function or something before displaying it?

---

@Igor:

Works great.

http://img200.imageshack.us/img200/4717/imageget.jpg

[ValueConversion(typeof(long), typeof(string))]
class FileSizeConverter : IValueConverter
{

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        string[] units = { "B", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB" };
        double size = (long)value;
        int unit = 0;

        while (size >= 1024)
        {
            size /= 1024;
            ++unit;
        }

        return String.Format("{0:0.#} {1}", size, units[unit]);
    }

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

Answer 1

Binding to a function is possible in WPF, but it’s generally painful. In this case a more elegant approach would be to create another property which returns a formatted string and bind to that.

class FileInfo {
  public int FileSizeBytes {get;set;}
  public int FileSizeFormatted {
   get{
     //Using general number format, will put commas between thousands in most locales.
     return FileSizeBytes.ToString("G");
   }
  }
}

In XAML, bind to FileSizeFormatted:

<DataGridTextColumn Binding="{Binding Path=FileSizeBytes, Mode=OneWay}" Header="Size" IsReadOnly="True" />

EDIT Alternative solution, thanks to Charlie for pointing this out.

You could write your own value converter by implementing IValueConverter.

[ValueConversion(typeof(int), typeof(string))]
public class IntConverter : IValueConverter {
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
        //needs more sanity checks to make sure the value is really int
        //and that targetType is string
        return ((int)value).ToString("G");
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
        //not implemented for now
        throw new NotImplementedException();
    }
}

Then in XAML:

<UserControl.Resources>
  <src:DateConverter x:Key="intConverter"/>
</UserControl.Resources>
...
<DataGridTextColumn Binding="{Binding Path=FileSizeBytes, Mode=OneWay, Converter={StaticResource intConverter}}" Header="Size" IsReadOnly="True" />