WP8 LongListSelector SelectedItem not bindable - xaml

Question

In WP8, they forgot to provide SelectedItem as a dependency property, hence I'm not able to bind to it. I fixed that using this: http://dotnet-redzone.blogspot.com/2012/11/windows-phone-8longlistselector.html
On doing so, I'm noticing that I'm not able to reset the property from the ViewModel, i.e. if I set the item to null in the ViewModel, it does not impact the UI. I have already provided two way binding in the UI but still setting the item to null in the ViewModel does not change the selected item in the LongListSelector. I also don't want to use the SelectionChanged event as I'm sharing ViewModels between WP7.5 app and a WP8 app, hence I want to push as much as I can into the ViewModel. Is there a solution for this?

Answer 1

It appears that the custom LongListSelector class that you are using does not handle the setter properly.
Replace the OnSelectedItemChanged callback with the following:
private static void OnSelectedItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var selector = (LongListSelector)d;
selector.SetSelectedItem(e);
}
private void SetSelectedItem(DependencyPropertyChangedEventArgs e)
{
base.SelectedItem = e.NewValue;
}

Answer 2

And there is full version of these two parts:
public class LongListSelector : Microsoft.Phone.Controls.LongListSelector
{
public LongListSelector()
{
SelectionChanged += LongListSelector_SelectionChanged;
}
void LongListSelector_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
SelectedItem = base.SelectedItem;
}
public static readonly DependencyProperty SelectedItemProperty =
DependencyProperty.Register(
"SelectedItem",
typeof(object),
typeof(LongListSelector),
new PropertyMetadata(null, OnSelectedItemChanged)
);
private static void OnSelectedItemChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var selector = (LongListSelector)d;
selector.SetSelectedItem(e);
}
private void SetSelectedItem(DependencyPropertyChangedEventArgs e)
{
base.SelectedItem = e.NewValue;
}
public new object SelectedItem
{
get { return GetValue(SelectedItemProperty); }
set { SetValue(SelectedItemProperty, value); }
}
}