DataBinding with MVVM Light tool kit

Question

I get some trouble with the binding using MVVM toolkit and would likr to knwo some advise if I do things correctly. First of all I have the View Model Locator which is defined as follow :

public class ViewModelLocator
{
    private static MainViewModel _main;
    private static ProductViewModel _product;

    /// <summary>
    /// Initializes a new instance of the ViewModelLocator class.
    /// </summary>
    public ViewModelLocator()
    {
        ////if (ViewModelBase.IsInDesignModeStatic)
        ////{
        ////    // Create design time view models
        ////}
        ////else
        ////{
        ////    // Create run time view models
        ////}

        CreateMain();
        CreateProduct();
    }

    /// <summary>
    /// Gets the Main property.
    /// </summary>
    public static MainViewModel MainStatic
    {
        get
        {
            if (_main == null)
            {
                CreateMain();
            }

            return _main;
        }
    }

    /// <summary>
    /// Gets the Main property.
    /// </summary>
    public static ProductViewModel ProductStatic
    {
        get
        {
            if (_product == null)
            {
                CreateProduct();
            }

            return _product;
        }
    }

    /// <summary>
    /// Gets the Main property.
    /// </summary>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance",
        "CA1822:MarkMembersAsStatic",
        Justification = "This non-static member is needed for data binding purposes.")]
    public MainViewModel Main
    {
        get
        {
            return MainStatic;
        }
    }

    /// <summary>
    /// Gets the Main property.
    /// </summary>
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance",
        "CA1822:MarkMembersAsStatic",
        Justification = "This non-static member is needed for data binding purposes.")]
    public ProductViewModel Product
    {
        get
        {
            return ProductStatic;
        }
    }

    /// <summary>
    /// Provides a deterministic way to delete the Main property.
    /// </summary>
    public static void ClearMain()
    {
        _main.Cleanup();
        _main = null;
    }

    /// <summary>
    /// Provides a deterministic way to create the Main property.
    /// </summary>
    public static void CreateMain()
    {
        if (_main == null)
        {
            _main = new MainViewModel();
        }
    }

    /// <summary>
    /// Provides a deterministic way to create the Main property.
    /// </summary>
    public static void CreateProduct()
    {
        if (_product == null)
        {
            _product = new ProductViewModel();
        }
    }

    /// <summary>
    /// Cleans up all the resources.
    /// </summary>
    public static void Cleanup()
    {
        ClearMain();
    }
}

Then I have my main window for which I set the datacontext as : DataContext="{Binding Source={x:Static vm:ViewModelLocator.MainStatic}}"

Inside my main window I have a list box which will have as ItemSource a collection of ProductViewModel define as follow :

 public class ProductViewModel : ViewModelBase
{

     SvcProduct.ProductServiceClient _clientSvc =new SvcProduct.ProductServiceClient() ;
     ObservableCollection<Product> _products = new ObservableCollection<Product>();


     public ObservableCollection<Product> Products
     {
         get { return _products; }
         set { _products = value; }
     }

    /// <summary>
    /// Initializes a new instance of the ProductViewModel class.
    /// </summary>
    public ProductViewModel()
    {
        ////if (IsInDesignMode)
        ////{
        ////    // Code runs in Blend --> create design time data.
        ////}
        ////else
        ////{
        ////    // Code runs "for real": Connect to service, etc...
        ////}
        _products=_clientSvc.GetProducts();

    }

    ////public override void Cleanup()
    ////{
    ////    // Clean own resources if needed

    ////    base.Cleanup();
    ////}
}

ProductViewModel return in Products the collection for the listbox. Each item in the list box is connected to a ProductView which is a userControl define as follow :

<UserControl
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:vm="clr-namespace:Solatys.Presentation.ViewModel"
mc:Ignorable="d"
x:Class="Solatys.Presentation.ProductView"
x:Name="UserControl"
d:DesignWidth="640" d:DesignHeight="480" Width="433" Height="319"
IsManipulationEnabled="True"
DataContext="{Binding Source={x:Static vm:ViewModelLocator.ProductStatic}}">

<Grid x:Name="LayoutRoot">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="144.3"/>
        <ColumnDefinition Width="0.64*"/>
        <ColumnDefinition Width="144.3"/>
    </Grid.ColumnDefinitions>
    <Grid.RowDefinitions>
        <RowDefinition Height="35" MaxHeight="35"/>
        <RowDefinition Height="130" MaxHeight="130"/>
        <RowDefinition Height="130" MaxHeight="130"/>
        <RowDefinition Height="24" MaxHeight="24"/>
    </Grid.RowDefinitions>
        <Image Source="Resources/beauté.jpg" Grid.Row="1" Stretch="UniformToFill" Grid.RowSpan="2" Grid.ColumnSpan="3"/>
    <TextBlock TextWrapping="Wrap" Grid.Column="1" Text="{Binding ProductName}" HorizontalAlignment="Center" VerticalAlignment="Center" FontSize="16" Foreground="White" FontFamily="Perpetua Titling MT" TextAlignment="Justify"/>
        <Border BorderBrush="Black" BorderThickness="0" Grid.Row="3" Grid.ColumnSpan="3">
            <Border.Background>
                <RadialGradientBrush>
                    <GradientStop Color="#00000000" Offset="1"/>
                    <GradientStop Color="#FF005E01"/>
                </RadialGradientBrush>
            </Border.Background>
            <TextBlock TextWrapping="Wrap" Text="Coup de Coeur" Foreground="White" HorizontalAlignment="Center" VerticalAlignment="Center" FontFamily="Perpetua" TextAlignment="Justify" FontSize="13.333"/>
        </Border>

        <Border Grid.Row="1" Grid.Column="0" Background="#7F000000" d:LayoutOverrides="Width">
            <TextBlock TextWrapping="Wrap"  Foreground="White" FontFamily="Perpetua" Margin="5"><Run Text="Type de produit"/><Run Language="fr-fr" Text=" : "/><LineBreak/><Run Language="fr-fr"/><LineBreak/><Run Language="fr-fr" Text="Produit de beauté Bio"/></TextBlock>
        </Border>

        <Border HorizontalAlignment="Right" Grid.Row="1" Grid.Column="2" Width="144.3" Height="130" Background="#7F000000">
            <TextBlock Margin="5" TextWrapping="Wrap" Foreground="White" FontFamily="Perpetua"><Run Text="Court descriptif"/><LineBreak/><Run/><LineBreak/><Run Language="fr-fr" Text="Ce nouveau produit reste notre coup de coeur pour ses propriétés naturelles ..."/></TextBlock>
        </Border>

        <Border HorizontalAlignment="Center" Grid.Row="2" Grid.Column="1" Width="144.3" Height="130" Background="#7F000000">
            <TextBlock TextWrapping="Wrap" Margin="5" Foreground="White" FontFamily="Perpetua"><Run Text="Caractéristiques du produit"/><Run Language="fr-fr" Text=" : "/><LineBreak/><Run Language="fr-fr"/><LineBreak/><Run Language="fr-fr" Text="- rajeunissant"/><LineBreak/><Run Language="fr-fr" Text="- vivifiant"/><LineBreak/><Run Language="fr-fr" Text="- prix attractif"/><LineBreak/><Run Language="fr-fr" Text="- produit contrôlé"/></TextBlock>
        </Border>

</Grid>

As you can see the above the DataContext is set to ViewModelLocator.ProductStatic but it says an error like "Cannot create instance of ViewModelLocator"

Due to that it seems that the binding is not operating as my list box is empty on my main Window

1- Any idea what I do wrong for that error? 2- In my scenario, how should I bind the ItemSource as the collection is a collection of ProductViewModel ?

regards serge

Answer 1

"Cannot create instance of ViewModelLocator" is typically a sign that something went wrong while the VMs were created. Try to put a breakpoint on _products=_clientSvc.GetProducts() then debug the code. I am pretty sure that something is going wrong in this method and an exception is thrown, which is causing the ViewModelLocator to fail too.

Cheers, Laurent