Slider not rendering font size of text on another page

Question

I am using a slider to control the font size of the text. On one page, I have the slider setup as follows:
<Grid Grid.Row="3" Margin="10,4.5,0.667,0">     <Slider x:Uid="FontSlider" x:Name="FontSlider" Header="Select font size" HorizontalAlignment="Left" VerticalAlignment="Top" Width="165" Margin="10,40,0,0" Height="65" Minimum="16" Maximum="32" ValueChanged="FontSizeChanged" LargeChange="8" SmallChange="8" TickFrequency="4" />            <TextBlock x:Uid="SampleText" Margin="207,63,11,169" Height="45" Text="Sample text" FontSize="{Binding ElementName=FontSlider, Mode=OneWay, Path=Value}" VerticalAlignment="Center" HorizontalAlignment="Center" Width="171" Style="{ThemeResource ListViewItemSubheaderTextBlockStyle}" TextWrapping="Wrap"/>        </Grid>
The slider is behaving as expected and the content binded to it  in the above textblock is also rendering properly.
However, when I try to bind the slider value to similar textblock on another page as below,  the font size of the text does not change. 
<TextBlock FontSize="{Binding ElementName=FontSlider, Mode=OneWay, Path=Value}" DataContext="{Binding}" Style="{ThemeResource ListViewItemSubheaderTextBlockStyle}" TextWrapping="WrapWholeWords"/>
I tried this with/without Style binding, but that does not helped either. How can I fix this?

Answer 1

Elements on a page cannot access elements on another page. You can do the binding through a view model. The Slider value will have a two-way binding to a property in the view model. The TextBlock in the other page will bind its FontSize to that view model
property.
It might be easier if you don't use binding on the other page. When the slider value changes (ValueChanged event), save the value to a global variable. In the other page OnNavigatedTo, set the TextBlock FontSize using the global variable.