ObservableCollection filter Selected Item

Question

I have a problem that I don't know how to solve.

I have a observable collection that I filter the items as I type in a textbox the problem is that when I select the filtered item I get the wrong selected index.

For example I have one item after filtering the real selected index is 2 but because it sets the collection as I type it set the index to one if the only filtered item left is one.

So how do I get the right item selected. Like in the mail application to make my question maybe easier to understand

Here is the selection changed event:

private void searchToDoItemsListBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    if (searchToDoItemsListBox.SelectedIndex == -1)
        return;
    NavigationService.Navigate(new Uri("/DetailsPage.xaml?selectedItemSearch=" + searchToDoItemsListBox.SelectedIndex, UriKind.Relative));
    searchToDoItemsListBox.SelectedIndex = -1;
}

And here is for the details page:

protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
    if (NavigationContext.QueryString.TryGetValue("selectedItemSearch", out selectedIndexSearch))
    {
        int indexSearch = int.Parse(selectedIndexSearch);
        DataContext = App.ViewModel.AllToDoItems[indexSearch];
    }

}

Answer 1

Bind to the SelectedItem

<ListBox SelectedItem="{Binding Selected, Mode=TwoWay}" ItemsSource="Binding={Items}">
</ListBox>

and you have to fields:

public ObservableCollection<ItemType> Items {get;set;} //setted while filtering, does it?

and

private ItemType _selected;
public ItemType Selected
{
  get 
  {
    return _selected;
  }
  set 
  { 
     _selected = value;
     //here you can save the item. 
     //For example save the item id, and navigate to DetailsPage
  }
}

And then, you can get the item from list:

protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
    {
        if (NavigationContext.QueryString.TryGetValue("selectedItemSearch", out selectedIndexSearch))
        {
            int id = int.Parse(selectedIndexSearch);
            DataContext = GetById(id)
        }
    }

  public ItemType GetByIf(id) 
  {
    for(int i = 0; i < App.ViewModel.AllToDoItems.Count; i++)
    {
        if(App.ViewModel.AllToDoItems[i].Id == id) return App.ViewModel.AllToDoItems[i];
    }
    return null;
  }