On Demand Data Loading in XamTree

[Infragistics] Mihail Mateev / Friday, January 28, 2011

The use of hierarchical data in applications often requires loading data on demand. This is very typical problem, especially when using WCF services from Silverlight applications.

Infragistics Silverlight controls as XamTree, XamDataTree, XamGrid offer an easy way to visualize these data. This article provides an example of the use of Infragistics XamTree with such data as the data loading is done in 2 different ways.
1. Downloading data at every level processing the events from the user interface of the client.
2. Using specially created by Infragistics VirtualCollection <T>, which can take data from the data source of parts on request.

To do that is created Silverlight Navigation Application and Silverlight-enabled WCF service, which returns the sample data.

Requirements:

Visual Studio 2010
Silverlight 4 Tools for Visual Studio 2010
Silverlight 4 (Silverlight Tools for Visual Studio 2010). WCF RIA Services are included in this installation.
Silverlight 4 Toolkit
One of these distributions:

Sample data:

Demo application uses a sample data from XML file. The only reason to use this file is to make sample easier to install and use. Data is about books and its chapters.

<?xml version="1.0" encoding="utf-8" ?>

<books>

  <book Title="The Elegant Universe" Author="Brian Greene" UnitPrice="15.95" Url="http://www.amazon.com/Elegant-Universe-Superstrings-Dimensions-Ultimate/dp/0393046885" ReleaseDate="02/01/1999" >

    <chapter Title="Tied Up with String" />

    <chapter Title="Space, Time, and the Eye of the Beholder" />

    <chapter Title="Of Warps and Ripples" />

    <chapter Title="Microscopic Weirdness" />

    <chapter Title="The Need for a New Theory: General Relativity vs. Quantum Mechanics" />

    <chapter Title="Nothing but Music: The Essentials of Superstring Theory" />

    <chapter Title="The &quot;Super&quot; in Superstrings" />

    <chapter Title="More Dimensions Than Meet the Eye" />

    <chapter Title="The Smoking Gun: Experimental Signatures" />

    <chapter Title="Quantum Gravity" />

    <chapter Title="Tearing the Fabric of Space" />

    <chapter Title="Beyond Strings: In Search of M-Theory" />

    <chapter Title="Black Holes: A String/M-Theory Perspective" />

    <chapter Title="Reflections on Cosmology" />

    <chapter Title="Prospects" />

  </book>

  

  <book Title="Dive Into Python" Author="Mark Pilgrim" UnitPrice="39.99" Url="http://www.amazon.com/Dive-Into-Python-Mark-Pilgrim/dp/1590593561" ReleaseDate="07/19/2004" >

    <chapter Title="Installing Python" />

    <chapter Title="Your First Python Program" />

    <chapter Title="Native Datatypes" />

    <chapter Title="The Power of Introspection" />

    <chapter Title="Objects and Object-Orientation" />

    <chapter Title="Exceptions and File Handling" />

    <chapter Title="Regular Expressions" />

    <chapter Title="HTML Processing" />

    <chapter Title="XML Processing" />

    <chapter Title="Scripts and Streams" />

    <chapter Title="HTTP Web Services" />

    <chapter Title="SOAP Web Services" />

    <chapter Title="Unit Testing" />

    <chapter Title="Test-First Programming" />

    <chapter Title="Refactoring" />

    <chapter Title="Functional Programming" />

    <chapter Title="Dynamic Functions" />

    <chapter Title="Performance Tuning" />

  </book>

  

  <book Title="The Selfish Gene (30th Anniversary Edition)" Author="Richard Dawkins" UnitPrice="15.95" Url="http://www.amazon.com/Selfish-Gene-Anniversary-Introduction/dp/0199291152" ReleaseDate="05/25/2006" >

    <chapter Title="Why are people?" />

    <chapter Title="The replicators" />

    <chapter Title="Immortal coils" />

    <chapter Title="The gene machine" />

    <chapter Title="Aggression: stability and the selfish machine" />

    <chapter Title="Genesmanship" />

    <chapter Title="Family planning" />

    <chapter Title="Battle of the generations" />

    <chapter Title="Battle of the sexes" />

    <chapter Title="You scratch my back, I'll ride on yours" />

    <chapter Title="Memes: the new replicators" />

    <chapter Title="Nice guys finish first" />

    <chapter Title="The long reach of the gene" />

  </book>

  

  <book Title="The Ideological Origins of the American Revolution (Enlarged Edition)" Author="Bernard Bailyn" UnitPrice="24.00" Url="http://www.amazon.com/Ideological-Origins-American-Revolution/dp/0674443020" ReleaseDate="03/01/1992" >

    <chapter Title="The Literature of Revolution" />

    <chapter Title="Sources and Traditions" />

    <chapter Title="Power and Liberty: A Theory of Politics" />

    <chapter Title="The Logic of Rebellion" />

    <chapter Title="Transformation" />

    <chapter Title="The Contagions of Liberty" />

    <chapter Title="Fulfillment: A Commentary on the Constitution" />

  </book>

  

  <book Title="Gödel, Escher, Bach: an Eternal Golden Braid" Author="Douglas R. Hofstadter" UnitPrice="20.00" Url="http://www.amazon.com/Godel-Escher-Bach-Douglas-Hofstadter/dp/B001IAM392" ReleaseDate="01/01/1999" >

    <chapter Title="The MU-puzzle." />

    <chapter Title="Meaning and Form in Mathematics." />

    <chapter Title="Figure and Ground." />

    <chapter Title="Consistency, Completeness, and Geometry." />

    <chapter Title="Recursive Structures and Processes." />

    <chapter Title="The Location of Meaning." />

    <chapter Title="The Propositional Calculus." />

    <chapter Title="Typographical Number Theory." />

    <chapter Title="Mumon and Gödel." />

    <chapter Title="Levels of Description, and Computer Systems." />

    <chapter Title="Brains and Thoughts." />

    <chapter Title="Minds and Thoughts." />

    <chapter Title="BlooP and FlooP and GlooP." />

    <chapter Title="On Formally Undecidable Propositions of TNT and Related Systems." />

    <chapter Title="Jumping out of the System." />

    <chapter Title="Self-Ref and Self-Rep." />

    <chapter Title="Church, Turing, Tarski, and Others." />

    <chapter Title="Artificial Intelligence: Retrospects." />

    <chapter Title="Artificial Intelligence: Prospects." />

    <chapter Title="Strange Loops, Or Tangled Hierarchies." />

  </book>

  

  <book Title="Silverlight 1.0" Author="Devin Rader, Jason Beres, J. Ambrose Little, Grant Hinkson" UnitPrice="23.37" Url="http://www.amazon.com/Silverlight-1-0-Devin-Rader/dp/0470228407" ReleaseDate="10/29/2007" >

   <chapter Title="Introduction to Silverlight" />

    <chapter Title="Building Silverlight Applications Using XAML" />

    <chapter Title="Designing Silverlight Applications Using Expression Blend 2"  />

    <chapter Title="Coding Silverlight Applications with JavaScript and XAML"  />

    <chapter Title="Using Silverlight with ASP.NET"  />

    <chapter Title="Silverlight 1.1 and the CLR"  />

    <chapter Title="Video Player: Silverlight 1.0 Case Example"  />

  </book>

  <book Title="Harry Potter and the Deathly Hallows" Author="J. K. Rowling" UnitPrice="20.99" Url="http://www.amazon.com/Harry-Potter-Deathly-Hallows-Book/dp/0545010225" ReleaseDate="07/21/2007" />

  <book Title="Silverlight 2 Silverlight 2 Programmer's Reference's Reference" Author="J. Ambrose Little, Jason Beres, Grant Hinkson, Devin Rader, Joe Croney" UnitPrice="31.49" Url="http://www.amazon.com/Silverlight-Programmers-Reference-Ambrose-Little/dp/0470385405" ReleaseDate="03/23/2009" />

  <book Title="Breaking Dawn (The Twilight Saga, Book 4)" Author="Stephenie Meyer" UnitPrice="12.64" Url="http://www.amazon.com/New-Moon-Twilight-Saga-Book/dp/0316024961" ReleaseDate="08/02/2008" />

  <book Title="The Last Lecture" Author="Randy Pausch and Jeffrey Zaslow" UnitPrice="13.17" Url="http://www.amazon.com/Last-Lecture-Randy-Pausch/dp/1401323251" ReleaseDate="04/08/2008" />

  <book Title="Brisingr" Author="Christopher Paolini" UnitPrice="16.50" Url="http://www.amzon.com/Brisingr-Inheritance-Book-Christopher-Paolini/dp/0375826726" ReleaseDate="09/20/2008" />

  <book Title="The Story of Edgar Sawtelle" Author="David Wroblewski" UnitPrice="14.27" Url="http://www.amazon.com/Story-Edgar-Sawtelle-Novel-Oprah/dp/0061768065" ReleaseDate="09/19/2008"  />

  <book Title="The Tales of Beedle the Bard" Author="J. K. Rowling" UnitPrice="7.14" Url="http://www.amazon.com/Tales-Beedle-Bard-Standard/dp/0545128285" ReleaseDate="12/04/2008" />

  <book Title="The Appeal" Author="John Grisham " UnitPrice="18.45" Url="http://www.amazon.com/Appeal-John-Grisham/dp/0385515049" ReleaseDate="01/29/2008" />

  <book Title="When You Are Engulfed in Flames" Author="David Sedaris" UnitPrice="15.59" Url="http://www.amazon.com/When-You-Are-Engulfed-Flames/dp/0316143472" ReleaseDate="06/03/2008" />

  <book Title="In Defense of Food: An Eater's Manifesto" Author="Michael Pollan" UnitPrice="13.17" Url="http://www.amazon.com/Defense-Food-Eaters-Manifesto/dp/1594201455" ReleaseDate="01/01/2008" />

  <book Title="The Revolution: A Manifesto" Author="Ron Paul" UnitPrice="13.17" Url="http://www.amazon.com/Host-Novel-Stephenie-Meyer/dp/031606804" ReleaseDate="04/01/2008" />

  <book Title="The Host: A Novel" Author="Stephenie Meyer " UnitPrice="13.17" Url="http://www.amazon.com/Host-Novel-Stephenie-Meyer/dp/031606804" ReleaseDate="05/06/2008" />

  <book Title="The Post-American World" Author="Fareed Zakaria" UnitPrice="17.13" Url="http://www.amazon.com/Post-American-World-Fareed-Zakaria/dp/039306235X" ReleaseDate="05/05/2008" />

  <book Title="Hungry Girl" Author="Lisa Lillien" UnitPrice="12.21" Url="http://www.amazon.com/Hungry-Girl-Survival-Strategies-Guilt-Free/dp/0312377428" ReleaseDate="04/29/2008" />

  <book Title="Fearless Fourteen (Stephanie Plum, No. 14)" Author="Janet Evanovich" UnitPrice="18.45" Url="http://www.amazon.com/Fearless-Fourteen-Stephanie-Plum-No/dp/0312349513" ReleaseDate="06/17/2008" />

  <book Title="The Tales of Beedle the Bard, Collector's Edition" Author="J. K. Rowling" UnitPrice="100.00" Url="http://www.amazon.com/Beedle-Collectors-Offered-Exclusively-Amazon/dp/0956010903" ReleaseDate="12/04/2008" />

  <book Title="Unaccustomed Earth" Author="Jhumpa Lahiri" UnitPrice="16.50" Url="http://www.amazon.com/Unaccustomed-Earth-Jhumpa-Lahiri/dp/0307265730" ReleaseDate="04/01/2008" />

  <book Title="sTORI Telling" Author="Tori Spelling" UnitPrice="16.47" Url="http://www.amazon.com/sTORI-Telling-Tori-Spelling/dp/1416950737" ReleaseDate="03/11/2008" />

  <book Title="Audition: A Memoir" Author="Barbara Walters" UnitPrice="19.77" Url="http://www.amazon.com/Audition-Memoir-Barbara-Walters/dp/030726646X"  ReleaseDate="05/06/2008" />

</books>

Steps to reproduce:

Download sample data
Create a sample Silverlight Navigation Application, hosted in an ASP.Net application.
Imeplement a Silverlight-enabled WCF service that returns collections of book and book chapters.
Create in the Silverlight application a MVVM using for data ObservabeCollection<T>
Create in the Silverlight application a MVVM using for data custom collections that inherits VirtualCollection<T>

WCF Service implementation:
XML file is read and stored in a static XDocument instance. All methods that returns collections of books or book chapters will use this instance to get fast required data. Sample application will visualize data. Data updates from UI are not implemented.

static string dataPath = HttpContext.Current.Server.MapPath(".") + Path.DirectorySeparatorChar +

onfigurationManager.AppSettings["DataDirectory"] + Path.DirectorySeparatorChar +

               ConfigurationManager.AppSettings["DataFile"];

  

static XDocument doc = XDocument.Load(dataPath);

Create a classes for Books and Chapters

Initially we will create classes for books and chapters of books to use in transporting data to the client.

#region BaseViewModel

[DataContract]

public abstract class BaseViewModel : INotifyPropertyChanged

{

  

    #region INotifyPropertyChanged Members

  

    public event PropertyChangedEventHandler PropertyChanged;

  

    #endregion

  

}

#endregion //BaseViewModel

  

#region Chapter

[DataContract]

public class Chapter : BaseViewModel

{

  

  

    #region Title

    private string _title;

  

    [DataMember]

    public string Title

    {

        get

        {

            return this._title;

        }

        set

        {

            if (this._title != value)

            {

                this._title = value;

            }

        }

    }

    #endregion //Title

}

#endregion //Chapter

  

#region Book

[DataContract]

public class Book : BaseViewModel

{

  

    #region Properties

  

    #region Author

    private string _author;

  

    [DataMember]

    public string Author

    {

        get

        {

            return this._author;

        }

        set

        {

            if (this._author != value)

            {

                this._author = value;

            }

        }

    }

    #endregion //Author

  

    #region ChaptersCount

    private int _chaptersCount;

  

    [DataMember]

    public int ChaptersCount

    {

        get

        {

            return this._chaptersCount;

        }

        set

        {

            if (this._chaptersCount != value)

            {

                this._chaptersCount = value;

            }

        }

    }

    #endregion //ChaptersCount

  

    #region Title

    private string _title;

  

    [DataMember]

    public string Title

    {

        get

        {

            return this._title;

        }

        set

        {

            if (this._title != value)

            {

                this._title = value;

            }

        }

    }

    #endregion //Title

  

    #region ReleaseDate

    private string _releaseDate;

  

    [DataMember]

    public string ReleaseDate

    {

        get

        {

            return this._releaseDate;

        }

        set

        {

            if (this._releaseDate != value)

            {

                this._releaseDate = value;

                //this.OnPropertyChanged("ReleaseDate");

            }

        }

    }

    #endregion //ReleaseDate

  

    #region UnitPrice

    private Decimal _unitPrice;

  

    [DataMember]

    public Decimal UnitPrice

    {

        get

        {

            return this._unitPrice;

        }

        set

        {

            if (this._unitPrice != value)

            {

                this._unitPrice = value;

                //this.OnPropertyChanged("UnitPrice");

            }

        }

    }

    #endregion //UnitPrice

  

    #region Url

    private string _url;

  

    [DataMember]

    public string Url

    {

        get

        {

            return this._url;

        }

        set

        {

            if (this._url != value)

            {

                this._url = value;

            }

        }

    }

    #endregion //Url

  

    #region Chapters

    private IEnumerable<Chapter> _chapters;

  

    [DataMember]

    public IEnumerable<Chapter> Chapters

    {

        get

        {

            return this._chapters;

        }

        set

        {

            if (this._chapters == null)

            {

                this._chapters = new ObservableCollection<Chapter>();

            }

            if (this._chapters != value)

            {

                this._chapters = value;

            }

        }

    }

    #endregion //Chapters

  

    #endregion //Properties

  

}

#endregion //Book

Create a static method GetBooks that returns IEnumerable<Book>:

private static IEnumerable<Book> GetBooks()

{

    //Return books as IEnumerable

    if (doc != null)

    {

  

        var dataSource = (from d in doc.Descendants("book")

                          where (d.Descendants("chapter") != null || d.Descendants("chapter").Count() >= 0)

                          select new Book

                          {

                              Author = d.Attribute("Author").Value,

                              Title = d.Attribute("Title").Value,

                              UnitPrice = d.Attribute("UnitPrice").GetDecimalValue(),

                              Url = d.Attribute("Url").Value,

                              ReleaseDate = d.Attribute("ReleaseDate").Value,

                              ChaptersCount = d.Descendants("chapter").Count()

                          });

  

        return dataSource.ToList();

    }

    return null;

}

Create an operation contract that calls the GetBooks method and return the result.

[OperationContract]

 public IEnumerable<Book> GetBookDataSource()

 {

  

     return GetBooks();

  

 }

Create a static method GetChapters(string url) that returns IEnumerable<Chapter> for a Book with a specific URL:

private static IEnumerable<Chapter> GetChapters(string url)

{

    //Return the chapters for a specified book

    if (doc != null)

    {

        var chapters = (from d in doc.Descendants("book")

                  where

                      (d.Attribute("Url").Value.Equals(url) && d.Descendants("chapter") != null &&

                       d.Descendants("chapter").Count() > 0)

                  select GetChapters(d));

  

        return chapters.First().ToList();

    }

  

    return null;

}

Chapters are created in the method GetChapters(XElement) :

private static IEnumerable<Chapter> GetChapters(XElement parent)

{

    return (from d in parent.Descendants("chapter")

            select new Chapter

            {

                Title = d.Attribute("Title").Value

            }).ToList<Chapter>();

}

Create an operation contract that calls the GetBookChapters method and return the result.

[OperationContract]

public IEnumerable<Chapter> GetBookChapters(string url)

{

    return GetChapters(url);

}

Client implementation:

Create in the Silverlight application a MVVM using for data ObservabeCollection<T>

ViewModel using an ObservableCollection<T>:

Create a BookDataViewModel class:

#region BookDataViewModel

public class BookDataViewModel : BaseViewModel

{

    #region Memrber Variables

  

    private BookDataSourceServiceClient _client;

  

    public event EventHandler<EventArgs> DataLoaded;

  

    #endregion //Memrber Variables

  

    #region Constructors

    public BookDataViewModel()

    {

        _client = new BookDataSourceServiceClient();

        _client.GetBookDataSourceCompleted += new EventHandler<GetBookDataSourceCompletedEventArgs>(ClientGetBookDataSourceCompleted);

        _client.GetBookDataSourceAsync();

    }

    #endregion //Constructors

  

    #region Properties

  

    #region Books

    private ObservableCollection<Book> _books;

    public ObservableCollection<Book> Books

    {

        get

        {

            if (this._books == null)

            {

                this._books = new ObservableCollection<Book>();

            }

            return this._books;

        }

        set

        {

            this._books = value;

            OnPropertyChanged("Books");

            if (this.DataLoaded != null)

            {

                EventArgs args = new EventArgs();

  

                this.DataLoaded(this, args);

            }

  

        }

    }

    #endregion //Books

  

    #region CurrentBook

    /// <summary>

    /// local variable _CurrentBook

    /// </summary>

    private Book _currentBook;

  

    /// <summary>

    /// Identifies the CurrentBook property.

    /// </summary>        

    public Book CurrentBook

    {

        get { return _currentBook; }

        set

        {

            _currentBook = value;

            OnPropertyChanged("CurrentBook");

        }

    }

    #endregion  //CurrentBook

  

    #endregion //Properties

  

  

    #region Methods

  

    #region GetChapters

    public void GetChapters(Book book)

    {

        if (_client == null)

        {

            _client = new BookDataSourceServiceClient();

        }

        CurrentBook = book;

  

        _client.GetBookChaptersCompleted -= ClientGetBookChaptersCompleted;

        _client.GetBookChaptersCompleted += new EventHandler<GetBookChaptersCompletedEventArgs>(ClientGetBookChaptersCompleted);

        _client.GetBookChaptersAsync(book.Url);

    }

    #endregion //GetChapters

  

    #endregion //Methods

  

    #region EventHandlers

  

    #region ClientGetBookChaptersCompleted

    void ClientGetBookChaptersCompleted(object sender, GetBookChaptersCompletedEventArgs e)

    {

        if (this.CurrentBook != null)

        {

            this.CurrentBook.Chapters = e.Result;

        }

  

    }

    #endregion //ClientGetBookChaptersCompleted

  

    #region ClientGetBookDataSourceCompleted

    void ClientGetBookDataSourceCompleted(object sender, GetBookDataSourceCompletedEventArgs e)

    {

        this.Books = e.Result;

    }

    #endregion //ClientGetBookDataSourceCompleted

  

    #endregion //EventHandlers

  

}

#endregion //BookDataViewModel

Create a view with XamTree, named XamTreeLazyLoadingView:

<ig:XamTree x:Name="dataTree" Width="370" ActiveItemChanged="DataTreeActiveItemChanged" ItemsSource="{Binding Books}" BorderThickness="0,0,0,0" Background="#FFFFFFFF" HorizontalAlignment="Left" ItemContainerStyle="{StaticResource XamTreeItemStyle}">

    <ig:XamTree.HierarchicalItemTemplate>

        <ig:HierarchicalDataTemplate ItemsSource="{Binding Chapters}">

            <ig:HierarchicalDataTemplate.ItemTemplate>

                <DataTemplate>

                    <StackPanel Orientation="Horizontal">

                        <Image Source="../Images/PageIcon.png" Width="16" Height="16" />

                        <TextBlock Text="{Binding Title}" Foreground="Gray" />

                    </StackPanel>

                </DataTemplate>

            </ig:HierarchicalDataTemplate.ItemTemplate>

            <DataTemplate>

                <StackPanel Orientation="Horizontal" MouseLeftButtonUp="StackPanel_MouseLeftButtonUp">

                    <Image Source="../Images/BookIcon.png" Width="16" Height="16"  />

                    <TextBlock Text="{Binding Title}" FontWeight="Bold"/>

                </StackPanel>

            </DataTemplate>

        </ig:HierarchicalDataTemplate>

    </ig:XamTree.HierarchicalItemTemplate>

</ig:XamTree>

Implement an event handler where when is raised double click over XamTreeItem in the root level (Book) a service client returns book chapters as IEnumerable<Chapter>

#region Constructors

public XamTreeLazyLoadingView()

{

  

    this._viewModel = Application.Current.Resources["BookDataViewModel"] as BookDataViewModel;

    InitializeComponent();

    if (this._viewModel != null)

    {

        this._viewModel.DataLoaded += new EventHandler<EventArgs>(ViewModelDataLoaded);

        this.DataContext = this._viewModel;

    }

  

}

#endregion //Constructors

  

...

  

#region ViewModelDataLoaded

void ViewModelDataLoaded(object sender, EventArgs e)

{

    this.DataContext = this._viewModel;

}

#endregion //ViewModelDataLoaded

  

....

  

#region StackPanel_MouseLeftButtonUp

private void StackPanel_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)

{

    var book = ((FrameworkElement)sender).DataContext as BookDataServiceReference.Book;

    if (book != null && (book.Chapters == null || book.Chapters.Count == 0))

    {

        if (!this.IgnoreMouseDown && (DateTime.Now.Ticks - this._doubleClickTimeStamp) <= 4000000)

        {

            this._viewModel.GetChapters(book);

            this.IgnoreMouseDown = true;

        }

  

        if (!this.IgnoreMouseDown)

        {

            this._doubleClickTimeStamp = DateTime.Now.Ticks;

        }

  

        this.IgnoreMouseDown = false;

  

    }

  

}

#endregion //StackPanel_MouseLeftButtonUp

Run the application:

A list with books is loaded

Select a specific book: Data for this book is visualized in the form in the right side of the Silverlight application.

Double click specific item. An event handler calls from WCF service all chapters for the selected book and expand this node.

Implementation using a VirtualCollection:

WCF Service implementation:

Implement a WCF methods and operation contracts that returns a range of books

private static IEnumerable<Book> GetBooks(int startIndex, int itemsCount)

{

    //Return range of books as IEnumerable

    if (doc != null)

    {

  

        var dataSource = (from d in doc.Descendants("book")

                          where (d.Descendants("chapter") != null || d.Descendants("chapter").Count() >= 0)

                          select new Book

                          {

                              Author = d.Attribute("Author").Value,

                              Title = d.Attribute("Title").Value,

                              UnitPrice = d.Attribute("UnitPrice").GetDecimalValue(),

                              Url = d.Attribute("Url").Value,

                              ReleaseDate = d.Attribute("ReleaseDate").Value,

                              ChaptersCount = d.Descendants("chapter").Count(),

                          });

  

  

        List<Book> lst = dataSource.ToList();

  

        itemsCount = Math.Min(lst.Count - 1 - startIndex, itemsCount);

  

        return lst.GetRange(startIndex, itemsCount);

    }

    return null;

}

[OperationContract(Name = "GetRangeBookDataSource")]

public IEnumerable<Book> GetBookDataSource(int startIndex, int itemsCount)

{

    return GetBooks(startIndex, itemsCount);

  

}

Implement a WCF methods and operation contracts that returns a range of book chapters .

private static IEnumerable<Chapter> GetChapters(string url, int startIndex, int itemsCount)

{

  

  

    //Return the range of chapters for a specified book

    if(doc != null) 

    {

  

  

        var chapters = (from d in doc.Descendants("book")

                        where

                            (d.Attribute("Url").Value.Equals(url) && d.Descendants("chapter") != null &&

                             d.Descendants("chapter").Count() > 0)

                        select GetChapters(d).ToList());

  

        if (chapters.Count() > 0 && chapters.First().Count > 0)

        {

            List<Chapter> lst = chapters.First();

            itemsCount = Math.Min(lst.Count - 1 - startIndex, itemsCount);

            var x1 = new Chapter[itemsCount];

  

            lst.CopyTo(0, x1, startIndex, itemsCount);

  

            return lst;                   

        }

  

  

    }

  

    return null;

}

[OperationContract(Name = "GetRangeBookChapters")]

public IEnumerable<Chapter> GetBookChapters(string url, int startIndex, int itemsCount)

{

    return GetChapters(url, startIndex, itemsCount);

}

Client implementation:

Create in the Silverlight application a MVVM using for data custom collections that inherits VirtualCollection<T>

ViewModel using an VirtualCollection<T>:

Create a BookViewModel class. When receive IEnumerable<T> from WCF service client generation could use several kind of collections, but not a custom collection. One possible solution is to use a separate view model in the client, where to add property for books that is VirtualCollection<T> or its inheritor.

public class BookViewModel : Book

{

    #region Constructors

    public BookViewModel(Book book)

    {

        this.Author = book.Author;

        this.Title = book.Title;

        this.Url = book.Url;

        this.ReleaseDate = book.ReleaseDate;

        this.UnitPrice = book.UnitPrice;

        this.Chapters = book.Chapters;

        this.ChaptersCount = book.ChaptersCount;

    }

    #endregion //Constructors

  

    #region Properties

  

    #region Client

    private BookDataSourceServiceClient _client;

    public BookDataSourceServiceClient Client

    {

        get

        {

            if (this._client == null)

            {

                this._client = new BookDataSourceServiceClient();

            }

            return this._client;

        }

        set

        {

            this._client = value;

            this.RaisePropertyChanged("Client");

        }

    }

  

    #endregion //Client

  

    #region BookChapters

    /// <summary>

    /// local variable _bookChapters

    /// </summary>

    private BookChaptersData _bookChapters;

  

    /// <summary>

    /// Identifies the Chapters property.

    /// </summary>        

    public BookChaptersData BookChapters

    {

        get

        {

            if (_bookChapters == null)

            {

                this._bookChapters = new BookChaptersData { Client = this.Client, ItemsCount = this.ChaptersCount, ChapterBook = this };

                this.RaisePropertyChanged("BookChapters");

            }

            return _bookChapters;

        }

        set

        {

            _bookChapters = value;

            this.RaisePropertyChanged("BookChapters");

        }

    }

  

    #endregion  //BookChapters

  

    #endregion //Properties

  

}

Implement BookSourceData: VirtualCollection<BookViewModel>:

#region BookSourceData

 public class BookSourceData : VirtualCollection<BookViewModel>

 {

     #region Member Variables

  

     private int _loadSize = 5;

     private int _startIndex = 0;

  

     #endregion //Member Variables

  

     #region Constructors

     public BookSourceData()

     {

  

         this.ItemDataRequested += new EventHandler<ItemDataRequestedEventArgs>(BookSourceData_ItemDataRequested);

         this.LoadSize = _loadSize;

         //this.AnticipatedCount = _itemsCount;

     }

     #endregion //Constructors

  

     #region Properties

  

     #region ItemsCount

     /// <summary>

     /// local variable _ItemsCount

     /// </summary>

     private int _itemsCount = 5;

  

     /// <summary>

     /// Identifies the ItemsCount property.

     /// </summary>        

     public int ItemsCount

     {

         get { return _itemsCount; }

         set

         {

             _itemsCount = value;

             this.AnticipatedCount = _itemsCount;

             this.LoadSize = _itemsCount;

             OnPropertyChanged("ItemsCount");

         }

     }

     #endregion  //ItemsCount

  

  

     #region Client

     private BookDataSourceServiceClient _client;

     public BookDataSourceServiceClient Client

     {

         get

         {

             if (this._client == null)

             {

                 this._client = new BookDataSourceServiceClient();

                 this._client.GetRangeBookDataSourceCompleted += new EventHandler<GetRangeBookDataSourceCompletedEventArgs>(ClientGetRangeBookDataSourceCompleted);

             }

             return this._client;

         }

         set

         {

             if (_client != null)

             {

                 _client.GetRangeBookDataSourceCompleted -= ClientGetRangeBookDataSourceCompleted;

             }

             this._client = value;

             this._client.GetRangeBookDataSourceCompleted += new EventHandler<GetRangeBookDataSourceCompletedEventArgs>(ClientGetRangeBookDataSourceCompleted);

         }

     }

     #endregion //Client

  

     #endregion //Properties

  

     #region EventHandlers

  

     #region BookSourceData_ItemDataRequested

     void BookSourceData_ItemDataRequested(object sender, ItemDataRequestedEventArgs e)

     {

         this._startIndex = e.StartIndex;

         this._client.GetRangeBookDataSourceAsync(e.StartIndex, e.ItemsCount);

     }

     #endregion //BookSourceData_ItemDataRequested

  

     #region ClientGetRangeBookDataSourceCompleted

     void ClientGetRangeBookDataSourceCompleted(object sender, GetRangeBookDataSourceCompletedEventArgs e)

     {

         if (e.Result != null)

         {

  

             ObservableCollection<BookViewModel> books = new ObservableCollection<BookViewModel>();

             foreach (Book b in e.Result)

             {

                 BookViewModel book = new BookViewModel(b);

                 book.Client = this.Client;

                 books.Add(book);

             }

             this.LoadItems(this._startIndex, books);

         }

  

     }

     #endregion //ClientGetRangeBookDataSourceCompleted

  

     #endregion //EventHandlers

  

 }

 #endregion //BookSourceData

Implement BookChaptersData: VirtualCollection<Chapter>

#region BookChaptersData

  

public class BookChaptersData : VirtualCollection<Chapter>

{

    #region Member Variables

  

    private int _loadSize = 10;

    private int _startIndex = 0;

  

    #endregion //Member Variables

  

    #region Constructors

  

    public BookChaptersData()

    {

        this.LoadSize = _loadSize;

        this.AnticipatedCount = _itemsCount;

        this.ItemDataRequested += new EventHandler<ItemDataRequestedEventArgs>(BookChaptersData_ItemDataRequested);

    }

  

    #endregion //Constructors

  

    #region Properties

  

    #region Client

    private BookDataSourceServiceClient _client;

    public BookDataSourceServiceClient Client

    {

        get

        {

            if (this._client == null)

            {

                this._client = new BookDataSourceServiceClient();

            }

            return this._client;

        }

        set

        {

            this._client = value;

            this.OnPropertyChanged("Client");

        }

    }

    #endregion //Client

  

    #region ChapterBook

    /// <summary>

    /// local variable _ChapterBook

    /// </summary>

    private BookViewModel _chapterBook;

  

    /// <summary>

    /// Identifies the ChapterBook property.

    /// </summary>        

    public BookViewModel ChapterBook

    {

        get { return _chapterBook; }

        set

        {

            _chapterBook = value;

            OnPropertyChanged("ChapterBook");

        }

    }

    #endregion  //ChapterBook

  

    #region ItemsCount

    /// <summary>

    /// local variable _ItemsCount

    /// </summary>

    private int _itemsCount = 5;

  

    /// <summary>

    /// Identifies the ItemsCount property.

    /// </summary>        

    public int ItemsCount

    {

        get { return _itemsCount; }

        set

        {

            _itemsCount = value;

            this.AnticipatedCount = _itemsCount;

            this.LoadSize = _itemsCount;

            OnPropertyChanged("ItemsCount");

        }

    }

    #endregion  //ItemsCount

  

    #endregion //Properties

  

    #region EventHandlers

  

    #region BookChaptersData_ItemDataRequested

    void BookChaptersData_ItemDataRequested(object sender, ItemDataRequestedEventArgs e)

    {

        if (this.ChapterBook == null)

        {

            return;

        }

  

        this._startIndex = e.StartIndex;

        this._client.GetRangeBookChaptersAsync(this.ChapterBook.Url, e.StartIndex, e.ItemsCount);

        this._client.GetRangeBookChaptersCompleted += new EventHandler<GetRangeBookChaptersCompletedEventArgs>(ClientGetRangeBookChaptersCompleted);

    }

    #endregion //BookChaptersData_ItemDataRequested

  

    #region ClientGetRangeBookChaptersCompleted

    void ClientGetRangeBookChaptersCompleted(object sender, GetRangeBookChaptersCompletedEventArgs e)

    {

        if (e.Result != null)

        {

            this.LoadSize = Math.Min(_loadSize, e.Result.Count);

  

            this.LoadItems(this._startIndex, e.Result);

  

        }

    }

    #endregion //ClientGetRangeBookChaptersCompleted

  

    #endregion //EventHandlers

}

  

#endregion //BookChaptersData

Create a BookDataVcViewModel class. It will be used as a DataContext for the view.

#region BookDataVcViewModel

public class BookDataVcViewModel : BaseViewModel

{

    #region Member Variables

    private BookDataSourceServiceClient _client;

    private int _booksCount;

    public event EventHandler<EventArgs> DataLoaded;

    #endregion //Member Variables

  

  

    #region Constructors

    public BookDataVcViewModel()

    {

        _client = new BookDataSourceServiceClient();

        _client.GetBookCountAsync();

        _client.GetBookCountCompleted += new EventHandler<GetBookCountCompletedEventArgs>(ClientGetBookCountCompleted);

    }

    #endregion //Constructors

  

    #region Properties

  

    #region Books

    private BookSourceData _books;

    public BookSourceData Books

    {

        get

        {

            if (this._books == null)

            {

  

                this._books = new BookSourceData();

  

            }

            return this._books;

        }

        set

        {

            this._books = value;

            OnPropertyChanged("Books");

            if (this.DataLoaded != null)

            {

                EventArgs args = new EventArgs();

  

                this.DataLoaded(this, args);

            }

  

        }

    }

    #endregion //Books

  

    #region CurrentBook

    /// <summary>

    /// local variable _CurrentBook

    /// </summary>

    private Book _currentBook;

  

    /// <summary>

    /// Identifies the CurrentBook property.

    /// </summary>        

    public Book CurrentBook

    {

        get { return _currentBook; }

        set

        {

            _currentBook = value;

            OnPropertyChanged("CurrentBook");

        }

    }

    #endregion  //CurrentBook

  

    #endregion //Properties

  

    #region EventHandlers

  

    #region ClientGetBookCountCompleted

    void ClientGetBookCountCompleted(object sender, GetBookCountCompletedEventArgs e)

    {

        _booksCount = e.Result;

        this.Books.Client = _client;

        this.Books.ItemsCount = _booksCount;

    }

    #endregion //ClientGetBookCountCompleted

  

    #endregion //EventHandlers

  

}

#endregion //BookDataVcViewModel

Create a view with XamTree, named XamTreeVCLazyLoadingView:

Implementation is a similar to the previous one, but simpler, because collections maintain requests to the WCF service.

<ig:XamTree x:Name="dataTree" Width="370" ActiveItemChanged="DataTreeActiveItemChanged" ItemsSource="{Binding Books}" BorderThickness="0,0,0,0" Background="#FFFFFFFF" HorizontalAlignment="Left" ItemContainerStyle="{StaticResource XamTreeItemStyle}">

    <ig:XamTree.HierarchicalItemTemplate>

        <ig:HierarchicalDataTemplate ItemsSource="{Binding BookChapters}">

            <ig:HierarchicalDataTemplate.ItemTemplate>

                <DataTemplate>

                    <StackPanel Orientation="Horizontal">

                        <Image Source="../Images/PageIcon.png" Width="16" Height="16" />

                        <TextBlock Text="{Binding Title}" Foreground="Gray" />

                    </StackPanel>

                </DataTemplate>

            </ig:HierarchicalDataTemplate.ItemTemplate>

            <DataTemplate>

                <StackPanel Orientation="Horizontal" >

                    <Image Source="../Images/BookIcon.png" Width="16" Height="16"  />

                    <TextBlock Text="{Binding Title}" FontWeight="Bold"/>

                </StackPanel>

            </DataTemplate>

        </ig:HierarchicalDataTemplate>

    </ig:XamTree.HierarchicalItemTemplate>

</ig:XamTree>

public partial class XamTreeVcLazyLoadingView : Page

{

    #region Member Variables

  

    private readonly BookDataVcViewModel _viewModel;

  

    #endregion //Member Variables

  

    #region Constructors

  

    public XamTreeVcLazyLoadingView()

    {

        this._viewModel = Application.Current.Resources["BookDataViewModelVC"] as BookDataVcViewModel;

        InitializeComponent();

        if (this._viewModel != null)

        {

            _viewModel.DataLoaded += new EventHandler<EventArgs>(ViewModelDataLoaded);

            this.DataContext = this._viewModel;                

        }

  

    }

  

    #endregion //Constructors

  

    #region Methods

  

    #region OnNavigatedTo

    // Executes when the user navigates to this page.

    protected override void OnNavigatedTo(NavigationEventArgs e)

    {

    }

    #endregion //OnNavigatedTo

  

    #endregion //Methods

  

    #region EventHandlers

  

    #region ViewModelDataLoaded

    void ViewModelDataLoaded(object sender, EventArgs e)

    {

        this.DataContext = this._viewModel;

    }

    #endregion //ViewModelDataLoaded

  

  

    #region DataTreeActiveItemChanged

    private void DataTreeActiveItemChanged(object sender, EventArgs e)

    {

        var book = dataTree.ActiveItem as BookViewModel; // BookDataServiceReference.Book;

        if (book != null)

        {

            if (bookGrid.Visibility == System.Windows.Visibility.Collapsed)

            {

                bookGrid.Visibility = System.Windows.Visibility.Visible;

            }

  

            bookGrid.DataContext = dataTree.ActiveItem;

        }

  

    }

    #endregion //DataTreeActiveItemChanged

  

  

    #endregion //EventHandlers

  

}

Run the application:

Select the page with implementation where is used a VirtualCollection:|
List with books is loaded. BookChaptersData collections are created for each BookViewModel. Now it is possible to understand witch books has information about chapters (books with chapters data have visible expanders).

Select a specific book: Data for this book is visualized in the form in the right side of the Silverlight application.

Double click specific item. When a BookChaptersData collection has expanded there has raised an event ItemDataRequiested from a virtual collection. BookChaptersData implementation gets from the WCF service required in this moment. The selected book node has expanded and user could see all book chapters.

Sample code could be downloaded here:

For implementation with a VirtualCollection you need to download the latest SR for NetAdvantage 2010 Vol.3.
If you have a trial version please ask Infragistics Developer Support for the latest Service Release for NetAdvantage 2010 Vol.3.