I needed to format a double into a sane format for an application I'm working on.

The data is somewhat more precise than I need.

I wanted to format the exposure time more reasonably with only a few decimal points rather than the 4000 digit number I seemed to be getting ... . So, a handy value Converter was needed to fix the problem:

    [ValueConversion(typeof(object), typeof(string))]

    public class ToStringFormatConverter : IValueConverter

    {

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)

        {

            string fmt = parameter as string;

            if (!string.IsNullOrEmpty(fmt))

            {

                return string.Format(culture, fmt, value);

            }

            else

            {

                return value.ToString();

            }

        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)

        {

            return null;

        }

    }

Then, using Binding and the Converter:

<TextBlock Text="{Binding Path=ExposureTime, Converter={StaticResource stringFormatConverter}, ConverterParameter={}{0:#0.0##}}" />

I needed to add to the resources section of my XAML file, an instance of this object:

<local:ToStringFormatConverter x:Key="stringFormatConverter"/>

The local namespace was added to the Window class (it could be added to any other root level WPF element like a page, etc):

xmlns:local="clr-namespace:MyApplicationNamespace"

To adjust the format, just change the ConverterParameter format shown above in red ({0:#0.0##}). This is just the normal ToString formatters that you have available in any .NET application. No gimmicks. The leading curly braces {} are used to escape the remainder of the string.

The ValueConversion attribute on the class I created is used to indicate to development environments and tools what types of inputs and outputs are expected to the function. In this case, it's always a string out, but the in varies.

Here was the result:

A nicely formatted number.