wp7: how to detect Listbox on screen visualized item?

In my application there is one Listbox and one textblock both are coupled inside a scrollviewer. Means I want to scroll both listbox and textblock together (following XAML may explain better ). I want to show some text in textblock from listbox which item is currently visible on screen. So I have to know which item is currently visible on screen.

Right now I have no clue what to do. Any suggestion or comment is appreciable. Thanks in advance.

<ScrollViewer  HorizontalScrollBarVisibility="Auto">

  <StackPanel>

    <ListBox x:Name="myListBox"  SelectionChanged="SelectinoChanged" Height="150">
      <ListBox.ItemsPanel>
        <ItemsPanelTemplate>
          <StackPanel Orientation ="Horizontal" >
            <StackPanel.RenderTransform>
              <TranslateTransform X="0"/>
            </StackPanel.RenderTransform>
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        </ItemsPanelTemplate>
      </ListBox.ItemsPanel>

      <ListBox.ItemTemplate>
        <DataTemplate>
          <StackPanel Orientation="Horizontal">
            <TextBlock Text="{Binding name}" FontSize="30"/>
            <Button Content="{Binding name}" FontSize="30" Name="but" Click="but_Click"/>
          </StackPanel>
        </DataTemplate>
      </ListBox.ItemTemplate>
    </ListBox>

    <TextBlock Name="tb" TextWrapping="Wrap" FontSize="40" Height="50" />

  </StackPanel>

</ScrollViewer>

---

the Listbox contains a ScrollViewer in it.

so you should just remove your ScrollViewer !

<StackPanel>
    <ListBox x:Name="myListBox>
        ...
    </ListBox>
    <TextBlock Name="tb"/>
</StackPanel>

and maybe set on the ListBox

HorizontalScrollBarVisibility="Auto"