Question

I’ve a CustomControl which use a ScrollViewer. The following code is an example which shows my use case in an easy way:

<Style TargetType="controls:MyCustomControl">
  <Setter Property="Template">
    <Setter.Value>
      <ControlTemplate TargetType="controls:MyCustomControl">
        <Grid x:Name="LayoutRoot" Background="White">
          <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="20"/>
            <RowDefinition Height="20"/>
          </Grid.RowDefinitions>
          <ScrollViewer x:Name="scrollViewer" Grid.Row="0"
                        Height="300" Width="400"
                        VerticalScrollBarVisibility="Auto" 
                        HorizontalScrollBarVisibility="Auto"
                        Style="{StaticResource ScrollViewerStyle}">
            <Canvas x:Name="outer" Width="400" Height="400"
                    Background="Red" Margin="50">
              <Canvas x:Name="inner" Background="Green" 
                      Width="400" Height="400">
                <Canvas.RenderTransform>
                  <ScaleTransform ScaleX="{Binding Value, ElementName=slider}"
                                  ScaleY="{Binding Value, ElementName=slider}"/>
                </Canvas.RenderTransform>
              </Canvas>
            </Canvas>
          </ScrollViewer>
        <Slider x:Name="slider" Minimum="0.1" Maximum ="10"
                Value="1" Grid.Row="2"/>
      </Grid>
    </ControlTemplate>
  </Setter.Value>
</Setter>

I left out the nonrelevant CodeBehind belonging to Slider.ValueChanged.

In a further question I ask How do I stick Controls inside of ScrollViewer. In this answer I got the idea to template the ScrollViewer. I added some elements to the ScrollViewer as shown in the answer. For example I’ve a new Canvas inside of my ScrollViewer:

<Canvas x:Name="canvas"/>

I need access to this Canvas at runtime, so in WPF I created:

public class MyScrollViewer : ScrollViewer

I override OnApplyTemplate and get access to it via GetTemplateChild. So all done.

In SL this way is not possible since ScrollViewer is sealed.

Now I am looking for an other way to get access. I hoped VisualTreeHelper would help me, but I do not get the Canvas. Neither in CodeBehind of my custom control nor in the codebehind of my MainPage (where I use my control).

private void GetCanvas(DependencyObject dependencyObject)
  {
    int count = VisualTreeHelper.GetChildrenCount(dependencyObject);
    for (int i = 0; i < count; i++)
    {
      DependencyObject child = VisualTreeHelper.GetChild(dependencyObject);
      Canvas canvas = child as Canvas;
      if (canvas == null)
      {
        GetCanvas(child);
      }
      else
      {
        // Code here if found
      }
    }
  }

Then a colleague remember me, that there exists the directive x:FieldModifier. I never used it before, just heard about it. I give it a try.

x:FieldModifier="public"

But no idea if it really give me the possibility to access from codebehind, even less how.

So, is there any way how I could access at my Canvas at runtime in Silverlight? Maybe there is maybe another solution in WPF itself, which also works on SL?

Answer 1

In Silverlight, this is possible using the extension method GetVisualDescendants(DependencyObject) in the Silverlight toolkit. The following should work…

• Add a reference to System.Windows.Controls.Primitives
• Add using System.Windows.Controls.Primitives
• Call scrollViewer.GetVisualDescendants().OfType().FirstOrDefault(canvas => canvas.Name.Equals(“yourCanvasName”)