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Consuming Odata Service in Windows Store Apps (Include MVVM Pattern)

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13 Feb 2013CPOL
Steps needed to consume an OData service in Windows Store Apps and use the MVVM Pattern and has Ioc container for managing the dependencies
  • Get the sample here

Introduction

This demo has the main goal to show the steps that are needed to consume an OData service in Windows Store Apps, and use the MVVM Pattern and has Ioc container for managing the dependencies.

Building the Sample

You only need Visual Studio 2012 and Windows 8, both the RTM version.

Description

For concretizing this sample, I used the Netflix OData Catalog API (Preview), that can be found where:

For those who is starting with OData service in Windows Store Apps, I recommend to install the:

“The WCF Data Services Tools for Windows Store Apps installer extends the Add Service Reference experience with client-side OData support for Windows Store Apps in Visual Studio 2012.”

Here are the main points:

  1. Creating a blank project like you can see in the image below
  2. Add Service Reference
  3. Analizing the NetflixService
  4. The IServiceManager, FakeServiceManager and ServiceManager
    1. The LoadNewDVDMoviesAsync method
    2. The LoadTopDVDMoviesAsync method
    3. The DataServiceContextAsyncExtension
    4. The model
  5. The TitlesViewModel
    1. The LoadDataAsync method
    2. The GroupView and ItemView
  6. Binding the view model with the view
    1. ViewModelLocator
    2. In App.xaml
    3. In the TitlesPage.xaml
    4. In the TitlesPage.xaml.cs
    5. Binding Data
  7. The output / running the demo
  8. Fiddler

Let’s Start

1. Create a Blank Project like you can see in the following image:

new project image

Note: I used te name Netflix.ClientApp (Win8) for the project, but I will change the namespace for Netflix.ClientApp and in the future if I need to create the Netflix.ClientApp (WP8, I can use the same namespace and if I need to “linked as” some file, I will not have problems with namespaces.

2. Add Service Reference

add reference

add metadata

The service reference that I added is: http://odata.netflix.com/v2/Catalog/.

3. Analyzing the NetflixService

The result will be:

add reference

Note: This is not required, but you can create a class diagram that will show all classes and its properties, method and events. It helps to understand that was added when you added the service reference.

class diagram

4. The IServiceManager, FakeServiceManager and the ServiceManager

Now the project has the service, and I decided to get the top of the DVD Movies and the new releases of the DVD Movies. With this, I will define an interface for my service manager.

Here is the code:

/// <summary>
/// Defines the service manager interface
/// </summary>
public interface IServiceManager
{
    /// <summary>
    /// Loads the new dvd movies async.
    /// </summary>
    /// <returns>
    /// Represents an asynchronous operation that return a IEnumerable.
    /// </returns>
    Task<IEnumerable> LoadNewDVDMoviesAsync();

    /// <summary>
    /// Loads the top dvd movies async.
    /// </summary>
    /// <returns>Represents an asynchronous operation that return a IEnumerable.</returns>
    Task<IEnumerable> LoadTopDVDMoviesAsync();
}

The fake implementation will be:

FakeServiceManager

/// <summary>
/// The fake service manager.
/// </summary>
public class FakeServiceManager : IServiceManager
{
    /// <summary>
    /// The bitmap soure
    /// </summary>
    private readonly BitmapImage _bitmapSoure;

    /// <summary>
    /// Initializes a new instance of the <see cref="FakeServiceManager" /> class.
    /// </summary>
    public FakeServiceManager()
    {
       _bitmapSoure = new BitmapImage(new Uri("ms-appx:///Images/FakeImage.png"));
    }

    /// <summary>
    /// Creates the items.
    /// </summary>
    /// <param name="number">The number.</param>
    /// <returns>the list of mytitles</returns>
    public IEnumerable CreateItems(int number)
    {
        var myTitles = new List<MyTitle>();
        for (var i = 0; i < number; i++)
        {
            myTitles.Add(new MyTitle
                    {
                        Name = string.Concat("Fake Name ", i),
                        AvailableFrom = DateTime.Now,
                        Rating = 0,
                        Image = _bitmapSoure
                    });
        }

        return myTitles;
    }

    /// <summary>
    /// Loads the new dvd movies async.
    /// </summary>
    /// <returns>
    /// Represents an asynchronous operation that return an IEnumerable.
    /// </returns>
    public async Task<IEnumerable> LoadNewDVDMoviesAsync()
    {
        return await Task.Run(() => CreateItems(20));
    }

    /// <summary>
    /// Loads the top dvd movies async.
    /// </summary>
    /// <returns>
    /// Represents an asynchronous operation that return an IEnumerable.
    /// </returns>
    public async Task<IEnumerable> LoadTopDVDMoviesAsync()
    {
        return await Task.Run(() => CreateItems(20));
    }
}

The implementation for the real service will be:

ServiceManager

public class ServiceManager : IServiceManager 
    { 
        /// <summary> 
        /// The _netflix catalog. 
        /// </summary> 
        private readonly NetflixCatalog _netflixCatalog; 

        /// <summary> 
        /// Initializes a new instance of the <see cref="ServiceManager"/> class. 
        /// </summary> 
        public ServiceManager() 
        { 
            _netflixCatalog = new NetflixCatalog(new Uri("http://odata.netflix.com/v2/Catalog/"), 
                              UriKind.Absolute); 
        } 

        /// <summary> 
        /// Loads the new dvd movies async. 
        /// </summary> 
        /// <returns> 
        /// Represents an asynchronous operation that return a IEnumerable. 
        /// </returns> 
        public async Task<IEnumerable> LoadNewDVDMoviesAsync() 
        { 
            var query = ((DataServiceQuery<Title>)_netflixCatalog.Titles.Where
                                                    (title => title.ReleaseYear >= 2012 
                                                     && title.Dvd.Available 
                                                     && title.Type == "Movie") 
                                                     .OrderByDescending(item => item.Dvd.AvailableFrom) 
                                                     .Take(30)).Expand(item => item.Genres).Expand
                                                     (item => item.Directors); 
            var result = await query.ExecuteAsync(); 

            return ConvertToMyTitles(result); 
        } 

        /// <summary> 
        /// Loads the top dvd movies async. 
        /// </summary> 
        /// <returns> 
        /// Represents an asynchronous operation that return a IEnumerable. 
        /// </returns> 
        public async Task<IEnumerable> LoadTopDVDMoviesAsync() 
        { 
            var query = ((DataServiceQuery<Title>)_netflixCatalog.Titles.Where
                                                     (title => title.ReleaseYear >= 2012 
                                                     && title.Dvd.Available 
                                                     && title.Type == "Movie") 
                                                     .OrderByDescending(item => item.AverageRating) 
                                                     .Take(20)).Expand(item => item.Genres).Expand
                                                     (item => item.Directors); 
            var result = await query.ExecuteAsync(); 

            return ConvertToMyTitles(result); 
        } 

        /// <summary> 
        /// Converts to my titles. 
        /// </summary> 
        /// <param name="titles">The titles.</param> 
        /// <returns>The my titles list.</returns> 
        private IEnumerable ConvertToMyTitles(IEnumerable<Title> titles) 
        { 
            return 
                titles.Select( 
                    title => 
                    new MyTitle 
                    { 
                        Name = title.Name, 
                        Image = new BitmapImage(new Uri(title.BoxArt.MediumUrl)), 
                        AvailableFrom = title.Dvd.AvailableFrom, 
                        Rating = title.AverageRating 
                    }).ToList(); 
        } 
    }

Here, there are two important methods:

  • LoadNewDVDMoviesAsync
  • LoadTopDVDMoviesAsync

4.1. The LoadNewDVDMoviesAsync Method

First, I will create the query that will be used for the service request:

  var query = ((DataServiceQuery<Title>)_netflixCatalog.Titles.Where( 
title => title.ReleaseYear >= 2012 &&  
title.Dvd.Available && 
title.Type == MovieStringValue) 
.OrderByDescending(item => item.Dvd.AvailableFrom) 
.Take(30)) 
.Expand(item => item.Genres) 
.Expand(item => item.Directors);

Here, I want all titles that release year is greater than 2012 and DVD is available and type is Movie and I want these title order by data from DVD is available. At the end, I only want the first 30 items and I want with Genres and Directors filled.

4.2. The LoadTopDVDMoviesAsync Method

In this method, the query will be:

var query = ((DataServiceQuery<Title>)_netflixCatalog.Titles.Where( 
title => title.ReleaseYear >= 2012 &&  
title.Dvd.Available && 
 title.Type == MovieStringValue) 
.OrderByDescending(item => item.AverageRating) 
.Take(20)) 
.Expand(item => item.Genres) 
.Expand(item => item.Directors);

Here, I want all titles for which release year is greater than 2012 and DVD is available and type is Movie and I want these titles ordered by average rating. At the end, I only want the first 20 items and I want with Genres and Directors properties filled.

4.3. The DataServiceContextAsyncExtensions

Inside both methods, I will execute the query like this:

var result = await query.ExecuteAsync();

and it will make a call to the server and request the data.

For simplicity of the calls, I added DataServiceContextAsyncExtension that allow to use the async and await keyworks.

/// <summary>
/// Defines the DataServiceContext Async Extensions
/// </summary>
public static class DataServiceContextAsyncExtensions
{
    /// <summary>
    /// Executes the async.
    /// </summary>
    /// <typeparam name="TResult">The type of the result.</typeparam>
    /// <param name="query">The query.</param>
    /// <returns>the task of the enumerable of the type TResult</returns>
    public static async Task<IEnumerable<TResult>> ExecuteAsync<TResult>
                      (this DataServiceQuery<TResult> query)
    {
        return await Task.Factory.FromAsync<IEnumerable<TResult>>
                    (query.BeginExecute(null, null), query.EndExecute);
    }
}

4.4 The Model

Here is the class diagram:

Image 6

GroupView is used to group a list of itemview that can have a MyTitle or Title object (depends if your view depends on the service data or not, if yes when there is an update, you may need to udpate the view and the viewmodel. If not, you only need to update the ConvertToMyTitles method in ServiceManager.

Note: This solution is good when you have for example:

Group 1 with a list of A data type elements and a Group 2 with a list of B data type elements.

You only need to create a similar class. I do so with MyTitleItemView or TitleItemView and the binding as easy and only need to define one ItemTemplateSelector that will choose the correct DataTemplate (normally by data type or group when both groups has the same data type).

5. The TilesViewModel

Because I am using the MVVM pattern, I will call these methods in my view model, I could implement it inside of the view model but I don't want to have dependencies in my view model.

In the view model, I will have:

/// <summary>
/// Initializes a new instance of the <see cref="TitlesViewModel"/> class.
/// </summary>
/// <param name="serviceManager">
/// The service Manager.
/// </param>
/// <param name="navigationService">
/// The navigation Service.
/// </param>
public TitlesViewModel(IServiceManager serviceManager, INavigationService navigationService)
{
    IsToShowProgress = true;
    _serviceManager = serviceManager;
    _navigationService = navigationService;
}

and inside the LoadDataAsync, I will have:

public async Task LoadDataAsync() 
        { 
            IsToShowProgress = true; 

            try 
            { 
                var newDVDMovies = _serviceManager.LoadNewDVDMoviesAsync(); 
                var topDVDMovies = _serviceManager.LoadTopDVDMoviesAsync(); 

                await Task.WhenAll(new Task[] { newDVDMovies, topDVDMovies }); 

                if (newDVDMovies.IsCompleted && topDVDMovies.IsCompleted) 
                { 
                    Groups = new List<GroupView> 
                                 { 
                                     ViewModelHelper.GetGroupView(NameDefinitions.TopDVDMoviesId, 
                                           NameDefinitions.TopDVDMoviesLabel, topDVDMovies.Result), 
                                     ViewModelHelper.GetGroupView(NameDefinitions.NewDVDMoviesId, 
                                           NameDefinitions.NewDVDMoviesLabel, newDVDMovies.Result) 
                                 }; 
                } 
                else 
                { 
                    ErrorMessage = GetErrorMessage(newDVDMovies, topDVDMovies); 
                } 

                IsToShowProgress = false; 
            } 
            catch (Exception exception) 
            { 
                IsToShowProgress = false; 

                // TODO: Define a better message error for the user 
                ErrorMessage = exception.Message; 
            } 
        }

Here, it is important to refer that I will do two service requests at the same time and wait until both are finished. This is great because I don´t need to request one by one and the time spent with the request is the maximum of both.

6. Binding the View Model with the View

6.1. ViewModelLocator

This class contains the SimpleIoc for dependency injection and helps to binding the view model with the view.

/// <summary>
/// This class contains static references to all the view models in the
/// application and provides an entry point for the bindings.
/// </summary>
public class ViewModelLocator
{
    /// <summary>
    /// Initializes a new instance of the ViewModelLocator class.
    /// </summary>
    public ViewModelLocator()
    {
        ServiceLocator.SetLocatorProvider(() => SimpleIoc.Default);

        if (!SimpleIoc.Default.IsRegistered<IServiceManager>())
        {
            // For use the fake data do:
            // SimpleIoc.Default.Register<IServiceManager, FakeServiceManager>();
            SimpleIoc.Default.Register<IServiceManager, ServiceManager>();
        }

        SimpleIoc.Default.Register<TitlesViewModel>();
    }

    /// <summary>
    /// Gets the titles view model.
    /// </summary>
    public TitlesViewModel TitlesViewModel
    {
        get
        {
            return ServiceLocator.Current.GetInstance<TitlesViewModel>();
        }
    }
}

6.2. In App.xaml

<viewModel:ViewModelLocator x:Key="Locator" d:IsDataSource="True" />

6.3. In the TitlesPage.xaml

DataContext="{Binding TitlesViewModel, Source={StaticResource Locator}}"

Here is defined the DataContext and with this all the page can be binding to the view model.

6.4. In the TitlesPage.xaml.cs

/// <summary>
/// Invoked when this page is about to be displayed in a Frame.
/// </summary>
/// <param name="e">Event data that describes how this page was reached.  The Parameter
/// property is typically used to configure the page.</param>
protected override async void OnNavigatedTo(NavigationEventArgs e)
{
    if (_titlesViewModel != null)
    {
        await _titlesViewModel.LoadDataAsync();
    }
}

Here is the moment the view model will load the data.

6.5 Binding Data

In TitlesPage.xaml, I have a CollectionViewSource that allows to define what is the source and in grouped data, which are the path of the Items.

<CollectionViewSource 

            x:Name="GroupedItemsViewSource" 

            Source="{Binding Groups}" 

            IsSourceGrouped="true" 

            ItemsPath="Items" 

            d:Source="{Binding Groups}"/>

This will help to group data in GridView.

<GridView 

                x:Name="ItemGridView"

                AutomationProperties.AutomationId="ItemGridView" 

                AutomationProperties.Name="Grouped Items" 

                Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2" 

                Visibility="{Binding IsToShowProgress, 
                Converter={StaticResource NagationBooleanToVisibilityConverter}}" 

                Padding="116,0,40,46" 

                IsSwipeEnabled="True" 

                IsItemClickEnabled="True" 

                ItemClick="ItemGridViewOnItemClick" 

                ItemsSource="{Binding Source={StaticResource GroupedItemsViewSource}}" 

                ItemTemplateSelector="{StaticResource NetFlixItemTemplateSelector}" 

                SelectionMode="Single" ItemContainerStyle="{StaticResource GridViewItemStyle}"> 
                <GridView.ItemsPanel> 
                        <ItemsPanelTemplate> 
                            <VirtualizingStackPanel Orientation="Horizontal"> 
                                <VirtualizingStackPanel.ChildrenTransitions> 
                                    <TransitionCollection> 
                                        <EntranceThemeTransition /> 
                                        <RepositionThemeTransition /> 
                                    </TransitionCollection> 
                                </VirtualizingStackPanel.ChildrenTransitions> 
                            </VirtualizingStackPanel> 
                        </ItemsPanelTemplate> 
                    </GridView.ItemsPanel> 
                <GridView.GroupStyle> 
                    <GroupStyle> 
                        <GroupStyle.HeaderTemplate> 
                            <DataTemplate> 
                                <Grid Margin="1,0,0,6"> 
                                    <Button 

                                        AutomationProperties.Name="Group Title" 

                                        Style="{StaticResource TextPrimaryButtonStyle}" > 
                                        <StackPanel Orientation="Horizontal"> 
                                            <TextBlock Text="{Binding Label}" 

                                                       Margin="3,-7,10,10" 

                                                       Style="{StaticResource GroupHeaderTextStyle}" /> 
                                            <TextBlock Text="{StaticResource ChevronGlyph}"  

                                                       FontFamily="Segoe UI Symbol"  

                                                       Margin="0,-7,0,10"  

                                                       Style="{StaticResource GroupHeaderTextStyle}"/> 
                                        </StackPanel> 
                                    </Button> 
                                </Grid> 
                            </DataTemplate> 
                        </GroupStyle.HeaderTemplate> 
                        <GroupStyle.Panel> 
                            <ItemsPanelTemplate> 
                                <VariableSizedWrapGrid Orientation="Vertical" Margin="0,0,80,0"/> 
                            </ItemsPanelTemplate> 
                        </GroupStyle.Panel> 
                    </GroupStyle> 
                </GridView.GroupStyle> 
            </GridView>

And the...

<templateSelector:NetFlixItemTemplateSelector x:Key="NetFlixItemTemplateSelector"/>

...will help to define the ItemTemplate that will be applied in each group.

Each item data template is defined in Template.xaml:

<DataTemplate x:Key="TopDVDMoviesItemTemplate"> 
        <Grid HorizontalAlignment="Left" Width="82" 

        Height="120" Background="#B9090B"> 
            <Image Source="{Binding Item.BoxArt.MediumUrl}"  

            Width="82" Height="120"  

             CacheMode="BitmapCache" Stretch="Uniform" /> 
        </Grid> 
    </DataTemplate> 

    <DataTemplate x:Key="NewDVDMoviesItemTemplate"> 
        <StackPanel Orientation="Horizontal" 

        HorizontalAlignment="Left" Width="300" Height="120"> 
            <Image  CacheMode="BitmapCache" Source="{Binding Item.BoxArt.MediumUrl}"   

             Width="82" Stretch="Uniform"  Margin="10,10,5,10"/> 
            <StackPanel  Margin="10,10,5,10"> 
                <TextBlock Text="{Binding Item.Name}" 

                TextWrapping="Wrap"  Margin="0,0,5,0"/> 
                <StackPanel Orientation="Horizontal" Margin="0,10,10,0"> 
                    <TextBlock  Margin="0,0,5,5" Text="Rating:" /> 
                    <TextBlock  Margin="0,0,0,5" Text="{Binding Item.AverageRating}" /> 
                </StackPanel> 
                <StackPanel Orientation="Vertical" Margin="0,0,10,0" > 
                    <TextBlock  Margin="0,0,0,5" Text="Available:"  /> 
                    <TextBlock Text="{Binding Item.Dvd.AvailableFrom,  
                                                   Converter={StaticResource StringFormatConverter}, 
                                                   ConverterParameter=\{0:d MMMM yyyy\}}"  

                                                   TextWrapping="Wrap"  /> 
                </StackPanel> 
            </StackPanel> 
        </StackPanel> 
    </DataTemplate>

7. The Output/Running the Demo

The result of the TitlesPage is:

Image 7

8. Fiddler

In fiddler, we can see the service requests:

Image 8

GET
/v2/Catalog/Titles()?$filter=ReleaseYear%20ge%202012%20and%20Dvd/Available%20and%20Type%20eq%20′Movie’
&$orderby=Dvd/AvailableFrom%20desc&$top=30&$expand=Genres,Directors
HTTP/1.1
GET
/v2/Catalog/Titles()?$filter=ReleaseYear%20ge%202012%20and%20Dvd/Available%20and%20Type%20eq%20′Movie’
&$orderby=AverageRating%20desc&$top=20&$expand=Genres,Directors
HTTP/1.1

Notes

For using Fiddler with Windows 8 Store Apps, the Win8 config is required to be installed.

See the Fiddler Extensions.

Other Notes

  1. Because I am using MVVM Light, from this library I used:
    • A ViewModelBase class to be used as the base class for ViewModels.
    • A ViewModelLocator class that comes with MVVM – Light serves two purposes:
      1. It allows you to locate your ViewModel from inside your XAML and hook it to the DataContext.
      2. It allows you to control two different ViewModels: a design time view model, and a run time ViewModel. Because one of the author’s goals of MVVM – Light is to make your XAML – ViewModel connection visible in blend (or ‘blendable’), the ViewModelLocator comes in handy for this purpose.
    • A SimpleIoc is a simple container for dependency injection.

      For more about MVVM Light, see http://mvvmlight.codeplex.com/.

    (It is not the unique solution.)

  2. Because this is a demo, maybe there are some points related with UI that are not completed, I focused on the propose of the sample. In the future, I would like to work more in this sample and implement more sample using this sample.

Source Code Files

The solution has the following structure:

Image 9

Details:

  • IServiceManager.cs has the IServiceManager interface and define the interface for the ServiceManager.
  • ServiceManager.cs has the ServiceManager class and it encapsulate the NetFlixService and exposes only the methods that are needed in ViewModel.
  • FakeServiceManager.cs is the implementation of the IServiceManager, but is a fake data.
  • TitlesViewModel.cs has TitlesViewModel class and it is used for binding with the DataContext from TitlesPage.
  • ViewModelLocator.cs has the ViewModelLocator class that helps to bind the view model with the view.
  • ViewModelHelper.cs has the ViewModelHelper class the helps to create grouped data.
  • TitlesPage.xaml and TitlesPage.xaml.cs that is the main page.
  • Templates.xaml is a resource dictionary that has the DataTemplate for the view.
  • NetFlixItemTemplateSelector.cs has the NetFlixItemTemplateSelector that is used for get the ItemTemplate for each item in gridView.

More Information

Run the sample

To debug the app and then run it, press F5 or use Debug > Start Debugging. To run the app without debugging, press Ctrl+F5 or use Debug > Start Without Debugging.

More Information

Ask me on twitter @saramgsilva

Official Source

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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