Question

I’m trying to implement pinch/stretch zooming on a ListBox:

<ListBox
   Grid.Row="1"
   ManipulationCompleted="ListBox_ManipulationCompleted"
   ItemsSource="{Binding Paras}">
   <ListBox.ItemTemplate>
     <DataTemplate>
       <TextBlock
         DataContext="{Binding}"
         TextWrapping="Wrap"
         Text="{Binding Text}"
         FontSize="{Binding FontSize}">
       </TextBlock>
     </DataTemplate>
   </ListBox.ItemTemplate>
 </ListBox>

What I really want to do is bind a RenderTransform to a Zoom property of my ViewModel but that’s not allowed. I can bind to the FontSize and it changes the FontSize correctly, but I have to hard code this in my code-behind. What I really want to do is honour the FontSize settings set by the designer and apply a uniform zoom to all the FontSizes. So in my code behind I have:

Style style = App.Current.Resources[_XElement.Name.LocalName] as Style;
if ( style != null )
{
  foreach ( var s in style.Setters )
  {
    Setter setter = s as Setter;
    if ( setter != null )
    {
        Debug.WriteLine(setter.Property + "=" + setter.Value);
    }
  }
}

I can’t access setter.Property.Name (compile time error) although I can see it is FontSize is in the debugger. And Value is always “Could not evaluate expression” – outputs as blank.

Any clues, either as to what’s going on here, or a better wayof doing it?

Andrew

Answer 1

You can’t access the Name because the Silverlight implemenation of DependencyProperty does not expose the name public. In order to pickup the Setters that set the FontSize property you will need to use a little reflection to pick out of the Style.TargetType a static field called “FontSizeProperty” and extract its value. Then compare each setter Property with that value if you have a match then you have found the setter reponsible for the FontSize.