Why does Path=SelectedItem.Content work for ComboBox in WPF but not Silverlight?

Question

The following code works fine in WPF.

In Silverlight it gives me the error **Invalid attribute value {Binding ElementName=WhichNumber, Path=SelectedItem.Content} for property Text. **

How can I get this to work in Silverlight?

    <ComboBox x:Name="WhichNumber" Width="100" HorizontalAlignment="Left" Margin="10" SelectedIndex="0">
        <ComboBoxItem Content="One"/>
        <ComboBoxItem Content="Two"/>
        <ComboBoxItem Content="Three"/>
    </ComboBox>

    <TextBlock Text="{Binding ElementName=WhichNumber, Path=SelectedItem.Content}"/>

Answer 1

Silverlight doesn't support Relative Binding (binding the attribute of one element to the value of another element's attribute value) while WPF has full support for that kind of binding.

Answer 2

Or you could move to Silverlight 3 which introduces UI element to element binding :)

For some reason (why they did this is beyond me), the syntax is slightly different, instead of writing when using WPF:

 <TextBlock Text="{Binding ElementName=WhichNumber, Path=SelectedItem.Content}"/>

you would write with Silverlight 3:

 <TextBlock Text="{Binding ElementName=WhichNumber, SelectedItem.Content}"/>

so without the 'Path=' part.

Unfortunately the Silverlight people at Microsoft have a tendency to make small changes to syntax and other things, rather than striving for easy code reuse across WPF and Silverlight.