Question

I am building a simple windown phone 7 Page. I’m doing MVVM (using MVVM light) and binding a List<Category> type property to ListPicker. This property is defined in a view model named AddExpenseViewModel like below

public class AddExpenseViewModel:ViewModelBase 
{
    public List<Category> Categories
    {
        get { return categories; }
        set
        {
            categories = value;
            RaisePropertyChanged("Categories");
        }
    }
}

Category class is defined as

public class Category
{
    public string Name { get; set; }
}

In my XAML I first define a resource as

<UserControl.Resources>
<bs:ViewModelLocator x:Key="ViewModelLocator" />
</UserControl.Resources>

Then set the DataContext of the grid that contains the ListPicker as

<Grid x:Name="ContentPanel" 
              Grid.Row="1" 
              Margin="13,1,11,-1" 
              DataContext="{Binding Path=AddExpenseViewModel, 
                                    Source={StaticResource ViewModelLocator}}">

And here is my XAML for ListPicker

<toolkit:ListPicker 
            HorizontalAlignment="Left" 
            Height="50" 
            Width="200" 
            Grid.Row="2" 
            Grid.Column="1" 
            DataContext="{Binding AddExpenseViewModel}"
            ItemsSource="{Binding Path=Categories, Mode=OneWay}" >
            <toolkit:ListPicker.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <Border Background="LightGreen" Width="*" Height="*">
                            <TextBlock Text="{Binding Name}"></TextBlock>
                        </Border>
                    </StackPanel>
                </DataTemplate>
            </toolkit:ListPicker.ItemTemplate>
</toolkit:ListPicker>`

This does not work. The ListPicker is always empty. Am I doing anything wrong here?

Answer 1

After lot of fire-fighting I got this to work myself. Here is what I changed to get this to work

I introduced a new class as below

public class Categories : ObservableCollection<Category>
{
}

Then I changed the property Categories on my AddExpenseViewModel as below

public Categories Categories
{
    get { return categories; }
    set
    {
        categories = value;
        RaisePropertyChanged("Categories");
   }
}
private Categories categories;

Then I changed the ItemsSource on listpicker as

ItemsSource="{Binding Path=Categories}"

This has got it working.