Presenting the ExpressionDescriptor

A couple of days ago i presented you the TypedList which supports navigation through subproperties. Another common feature request is the possibility to add a column that has a value based on other values in the row (like a DataColumn with it’s Expression property set). With the plumbing code i’ve written it’s as simple as implementing the following interface:

public interface IExpressionProvider<ComponentType, PropertyType>
{
 /// <summary>
 /// Gets the name of the property
 /// </summary>
 string Name { get; }

 /// <summary>
 /// Returns the value of the expression for the given component
 /// </summary>
 /// <param name="component"></param>
 /// <returns></returns>
 PropertyType GetValue(ComponentType component);
}

An example implementation could be an expression that represents the duration of an Appointment:

public class DurationExpressionProvider : IExpressionProvider<Appointment, TimeSpan>
{
 #region IExpressionProvider<Appointment,TimeSpan> Members

 public string Name { get { return "||Duration"; } }

 public TimeSpan GetValue(Appointment component)
 {
  return component.DateTimeRange.End - component.DateTimeRange.Start;
 }

 #endregion
}

I’ve changed the constructor of TypedList a bit so that it accepts an enumeration of PropertyDescriptors. In my example you can initialise the list as following:

List<PropertyDescriptor> propertyDescriptors = new List<PropertyDescriptor>();

// create the subpropertydescriptors
string[] propertyNames = new string[] { "Patient.Name", "Patient.Address.Municipality", "DateTimeRange.Start", "DateTimeRange.End" };
propertyDescriptors.AddRange(Array.ConvertAll<string, SubPropertyDescriptor<Appointment>>(propertyNames, delegate(string propertyName) { return new SubPropertyDescriptor<Appointment>(propertyName); }));

// add an expressiondescriptor
IExpressionProvider<Appointment, TimeSpan> expressionProvider = new DurationExpressionProvider();
ExpressionDescriptor<Appointment, TimeSpan> durationDescriptor = new ExpressionDescriptor<Appointment, TimeSpan>(expressionProvider);
propertyDescriptors.Add(durationDescriptor);

TypedBindingList<Appointment> appointments = new TypedBindingList<Appointment>(propertyDescriptors);

And this is how it looks like at runtime:

As always, feel free to download the code: TypedList.zip.