C#, Silverlight/Telerik: RadMultiSelectDropDownDataField

RadMultiSelectDropDownDataField.cs

using System;
using System.Windows.Controls;
using GalaSoft.MvvmLight.Messaging;
using Telerik.Windows.Controls;

namespace Fox.Xavier.Client.Views
{
    using Fox.Silverlight.Controls;
    using Fox.Silverlight.Models;

    public class RadMultiSelectDropDownDataField : DataFormDataField
    {
        protected override Control GetControl()
        {
            var dropdown = new MultiSelectDropDown
            {
                DisplayMemberPath = "DisplayText",
                DropDownSummaryFormat = "{0} departments selected",
                SelectedValuePath = "Id"
            };

            if (this.Tag == null) throw new NullReferenceException("The expected Tag is not here.");

            var content = new LightContentForFrameworkElement<MultiSelectDropDown>
            {
                Element = dropdown,
                DataOfContext = this.DataContext
            };
            var message = new LightMessage<LightContentForFrameworkElement<MultiSelectDropDown>>(content)
            {
                Source = LightMessageSource.ViewAddedChildren,
                UniqueId = this.Tag.ToString()
            };
            Messenger.Default.Send(message);
            return dropdown;
        }
    }
}