Thread-safe Silverlight Cairngorm

using System;
using System.Collections.Generic;

using SilverlightCairngorm;
using SilverlightCairngorm.Model;
using System.Windows.Media.Imaging;

namespace SilverlightCairngormDemo.Model
{
	public class SilverPhotoModel : ModelLocator
	{
		private static readonly SilverPhotoModel _instance = new SilverPhotoModel();

		/// <summary>
		/// Returns the single instance of the app model
		/// </summary>
		/// <returns>single instance of the app model</returns>
		public static SilverPhotoModel Instance { get { return _instance; } }

		// Explicit static constructor to tell C# compiler
		// not to mark type as beforefieldinit
		static SilverPhotoModel()
		{
		}

		/// <summary>
		/// Private constructor for singeltom object
		/// </summary>
		private SilverPhotoModel() : base()
		{
		}

		private List<FlickRPhoto> _photoList = new List<FlickRPhoto>();
		/// <summary>
		/// Data model for search result data binding
		/// </summary>
		public List<FlickRPhoto> PhotoList
		{
			get { return _photoList; }
			set
			{
				_photoList = value; 
				NotifyPropertyChanged("PhotoList"); 
			}
		}

		private int _selectedIdx = -1;

		/// <summary>
		/// Data model for selected photo index
		/// </summary>
		public int SelectedIdx
		{
			get 
			{ 
				return _selectedIdx; 
			}
			set
			{
				_selectedIdx = value;
				NotifyPropertyChanged("SelectedPhotoSource");
				NotifyPropertyChanged("SelectedIdx");
			}
		}

		/// <summary>
		/// Read-only property for image displaying
		/// </summary>
		public string SelectedPhotoSource
		{
			get 
			{
				return (_selectedIdx < 0 || PhotoList.Count < 2) ? "" : PhotoList[_selectedIdx].ImageUrl;
			}
		}

		private string _searchTerm = "Cairngorm";
		/// <summary>
		/// Data model for search term
		/// </summary>
		public string SearchTerm
		{
			get { return _searchTerm; }
			set { _searchTerm = value; /*NotifyPropertyChanged("SearchTerm");*/ }
		}

		private bool _readySearchAgain = true;
		/// <summary>
		/// to prevent search again before previous search returns
		/// </summary>
		public bool ReadySearchAgain
		{
			get { return _readySearchAgain; }
			set { _readySearchAgain = value; NotifyPropertyChanged("ReadySearchAgain"); }
		}

	}
}