A contestant in the BALL Watch Silverlight Contest was working on creating his entry (Due August 5, 2010) and sent me a question on data binding to the day of the week.  The watch that he is creating displays the day abbreviated and capitalized and he wanted to use data binding like I showed in this tutorial. Since the Chronograph control exposes a DateTime Date property, he could bind to that and use Date.DayOfWeek property, but that would return values like Monday and  Tuesday, not MON and TUE.  The solution in this case is to create a value converter and use that in the binding. 

A Value Converter Item Template

I create value converters so often in my Silverlight and WPF development, that I created a C# item template that I use over and over in Visual Studio.  I’ve posted the item template to the Visual Studio Gallery so you can use it too.  The Visual Studio Gallery is integrated with Visual Studio 2010, so you can install and start using the template right from Visual Studio:

1. In your Silverlight project in Visual Studio 2010, select Project…Add New Item…
2. Select Online Templates on the left and then the Silverlight group
3. Select Value Converter, type a name for your converter at the bottom, and press Add
   

If you want to create your own project or item templates for Visual Studio 2010 and share them like this on the Visual Studio Gallery, you should first download and install the Visual Studio SDK and then create a VSIX Project from Visual Studio with the item template .zip its contents.

The DayOfWeekConverter Class

1. Add this DayOfWeekConverter.cs to your Silverlight project (code below and attached), changing the namespace as appropriate
2. In Expression Blend 4, build the project
3. If you haven’t done so already, add a TextBlock to the scene or control template, select it, and in the property editor for the Text property click on the white box to the right of the text and select Data Binding
4. In the extended properties for the Data Binding, select Date as the Custom Path Expression and a DayOfWeekConverter for the Value Converter
5. For Template Binding, you will need to do one more step – edit the XAML to specify the RelativeSource for the binding by adding a RelativeSource={RelativeSource TemplatedParent} parameter to the binding (line broken below to illustrate):
   

   <TextBlock 
       Text="{Binding Date, Converter={StaticResource DayOfWeekConverter1}, 
              RelativeSource={RelativeSource TemplatedParent}}"/>

DayOfWeekConverter.cs

namespace SilverlightApplication6
{
    using System;
    using System.Windows;
    using System.Windows.Data;

    /// <summary>
    /// Value Converter for converting DateTime to 3-letter capitalized abbreviations
    /// </summary>
    public class DayOfWeekConverter : IValueConverter
    {
        #region IValueConverter Members
        
        /// <summary>
        /// Convert a DayOfWeek to a 3-letter capitalized abbreviation (MON, TUE, WED, THU, FRI, SAT, SUN)
        /// </summary>
        /// <param name="value">a DateTime</param>
        /// <param name="targetType">the target type to convert to</param>
        /// <param name="parameter">an unused parameter</param>
        /// <param name="culture">an unused culture</param>
        /// <returns>null or the 3-letter capitalized abbreviation</returns>
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            if (value == null)
            {
                return null;
            }

            var date = (DateTime)value;

            var dayOfWeek = date.DayOfWeek;

            var abbreviated = dayOfWeek.ToString().ToUpperInvariant().Substring(0, 3);

            return abbreviated;
        }

        /// <summary>
        /// Not Supported conversion
        /// </summary>
        /// <param name="value">the value to convert back</param>
        /// <param name="targetType">the target type</param>
        /// <param name="parameter">the parameter</param>
        /// <param name="culture">the culture</param>
        /// <returns> a <see cref="DependencyProperty.UnsetValue"/></returns>
        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return DependencyProperty.UnsetValue;
        }

        #endregion
    }
}