WinRT XAML Toolkit BindableSelections not updating UI - xaml

Question

Below is the xaml and c# code for handling selected items in my gridview.
I am also using MVVM Light and everything is working, including me being able to see what's inside SelectedItems.
However I when I attempt to clear the SelectedItems, my UI doesn't seem to update/reflect the changes made to SelectedItems.
I am using WinRT XAML Toolkit (http://winrtxamltoolkit.codeplex.com/) which has the BindableSelection extension on a GridView
XAML
<controls:CustomGridView
x:Name="VideoItemGridView"
Grid.Row="2"
Margin="0,-3,0,0"
Padding="116,0,40,46"
HorizontalContentAlignment="Stretch"
VerticalContentAlignment="Stretch"
IsItemClickEnabled="True"
SelectionMode="Extended"
Extensions:GridViewExtensions.BindableSelection="{Binding SelectedVideoItems, Mode=TwoWay}"
ItemsSource="{Binding Source={StaticResource ViewSource}}"
ItemTemplate="{StaticResource VideoItemTemplate}">
<GridView.ItemsPanel>
<ItemsPanelTemplate>
<VariableSizedWrapGrid ItemWidth="250" ItemHeight="160" />
</ItemsPanelTemplate>
</GridView.ItemsPanel>
</controls:CustomGridView>
MyViewViewModel.cs
#region Selected Items
/// <summary>
/// Gets or sets the selected video items.
/// </summary>
public ObservableCollection<object> SelectedVideoItems
{
get { return this._selectedVideoItems; }
set
{
this._selectedVideoItems = value;
this.Set("SelectedVideoItems", ref this._selectedVideoItems, value);
}
}
private ObservableCollection<object> _selectedVideoItems = new ObservableCollection<object>();
#endregion
#region App Bar Click Commands
/// <summary>
/// Gets the ClearSelection click command.
/// </summary>
public ICommand ClearSelectionClickCommand
{
get
{
return new RelayCommand(() => this.ClearSelectionOperation());
}
}
/// <summary>
/// Selects all command operation.
/// </summary>
private void ClearSelectionOperation()
{
this.SelectedVideoItems = new ObservableCollection<object>();
}
#endregion

Answer 1

Try clearing your selected items in ClearSelectionOperation by calling
this.SelectedVideoItems.Clear();
instead of
this.SelectedVideoItems = new ObservableCollection<object>();
If that doesn't help check if the current version of the extension from March 7 fixes the problem.

Answer 2

It turns out that since I am using a data template, it is actually my data model that needed to set a flag to indicate it is selected
Here's the missing piece of the puzzle. Once I update the data model bound to the grid view item (which also includes support for row/col spanning), the UI updated as expected.
Hope this helps others.
public class CustomGridView : GridView
{
protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
{
try
{
base.PrepareContainerForItemOverride(element, item);
dynamic _Item = item;
element.SetValue(VariableSizedWrapGrid.ColumnSpanProperty, _Item.ColumnSpan);
element.SetValue(VariableSizedWrapGrid.RowSpanProperty, _Item.RowSpan);
element.SetValue(GridViewItem.IsSelectedProperty, _Item.IsSelected);
}
catch
{
element.SetValue(VariableSizedWrapGrid.ColumnSpanProperty, 1);
element.SetValue(VariableSizedWrapGrid.RowSpanProperty, 1);
element.SetValue(GridViewItem.IsSelectedProperty, false);
}
finally
{
base.PrepareContainerForItemOverride(element, item);
}
}