Passing Object rather than selectedIndex from Databound listbox - windows-phone-7

Question

I'm having an issue when I try to pass the selectedIndex of my list from my "List" screen.
On my List screen I have the following binding:
Code Behind:
lbPrograms.ItemsSource = App.ViewModel.Items;
XAML:
<ListBox x:Name="lbPrograms" ItemsSource="{Binding Items}" SelectionChanged="lbPrograms_SelectionChanged">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel x:Name="DataTemplateStackPanel" Orientation="Horizontal">
<Image x:Name="ItemImage" Source="/images/ArrowImg.png" Height="43" Width="43" VerticalAlignment="Top" Margin="10,0,20,0"/>
<StackPanel>
<TextBlock x:Name="ItemText" Text="{Binding programName}" Margin="-2,-13,0,0" Style="{StaticResource PhoneTextExtraLargeStyle}"/>
<TextBlock x:Name="DetailsText" Text="{Binding createDate}" Margin="0,-6,0,3" Style="{StaticResource PhoneTextSubtleStyle}"/>
<TextBlock x:Name="programId" Text="{Binding programId}" Margin="0,-6,0,3" Style="{StaticResource PhoneTextSubtleStyle}"/>
</StackPanel>
<!--<Image x:Name="ItemFavs" Source="/images/favs.png" Height="43" Width="43" VerticalAlignment="Top" Margin="10,0,20,0"/>
<Image x:Name="ItemDelete" Source="/images/delete.png" Height="43" Width="43" VerticalAlignment="Top" Margin="10,0,20,0"/>-->
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
In my detail screen I look up using the selectedIndex value:
App.ViewModel.Refresh();
DataContext = App.ViewModel.Items[index].nValDictionary;
However, since I can't figure out how to just update a value in my iEnumerable collection I have been removingAt[index] and then re-adding to the collection.
So can anyone tell me, how do use update an existing element in my collection? If not, can I pass the programId (that is in my binding) instead of the selectedIndex as the indexes are getting all messed up after the Delete/Add functionality.
Please Advise.
UPDATE:
After speaking in several forums I should clear up that I am implement INotifyChanged Event on my properties in my object.
Basically the following snippet of code is my current issue:
private void FavBtn_Click(object sender, EventArgs e)
{
foreach (var item in App.ViewModel.Items)
{
if ((item.currentProgram == true) && (item.programId != index))
{
item.currentProgram = false;
}
if (item.programId == index)
{
item.currentProgram = true;
}
}
When I run this everything looks to be ok.
However, when I navigate to another page, I re-load the object and the changes are lost. It is almost like I need to save them before navigating, however, if I do a item.Save(); I get duplicates in my list.

Answer 1

I'm guessing you haven't implemented INotifyPropertyChanged on your Items class yet.
Implementing this will allow updates made in these objects to be updated through your data bindings.
Here's a walkthrough on how to implement INotifyPropertyChanged.
How to: Implement the INotifyPropertyChanged Interface

Answer 2

Is App.ViewModel.Items of type ObservableCollection<T>?
If so, when you modify a property of one of the collection items and raise a property change event (via INotifyPropertyChanged) indicating the collection property that your ListBox.ItemsSource is bound to, the DataTemplate bindings will do the rest.