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up vote 2 down vote favorite

So i have a style for a treeview that is failing to bind correctly. I have bound height to the graph height property of the user control the style is used in. However, it doesn't find the user control for some unknown reasons. I was hoping someone could shed some light on the issue. Is it forbidden to bind a property of a template to something other than the templated parent? And why can't it find the element just because it is in a style.

From the beginning of the xaml file:

<UserControl 
  x:Class="WpfExperimental.GraphViewer"
  x:Name="graph_viewer"

and then the style:

   <Style x:Key="SignalNameTreeViewStyle" TargetType="TreeView">
      <Setter Property="OverridesDefaultStyle" Value="True" />
      <Setter Property="SnapsToDevicePixels" Value="True" />
      <Setter Property="Template">
        <Setter.Value>
          <ControlTemplate TargetType="TreeView">
            <ScrollViewer x:Name="SignalNameTreeView_ScrollViewer" HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Hidden">
              <StackPanel>
                <wpfExp:SignalNameBox x:Name="TreeViewTimeTextBox" Grid.Row="0" Grid.Column="0"
                      Height="{Binding ElementName=graph_viewer, Path=GraphHeight, Mode=OneWay}"
                      Width="200"
                      Margin="19,0,0,0"
                      MainText="Time" 
                    />
                <ItemsPresenter/>
              </StackPanel>         
            </ScrollViewer>
            <ControlTemplate.Triggers>
              <Trigger Property="ItemsControl.HasItems" Value="False">
                <Setter TargetName="TreeViewTimeTextBox"
                        Property="Visibility"
                        Value="Collapsed"/>
              </Trigger>
            </ControlTemplate.Triggers>
          </ControlTemplate>
        </Setter.Value>
      </Setter>
    </Style>

Currently I get data binding errors from this attempt to bind

ystem.Windows.Data Error: 39 : BindingExpression path error: 'GraphHeight' property not found on 'object' ''UserControl' (Name='graph_viewer')'. BindingExpression:Path=GraphHeight; DataItem='UserControl' (Name='graph_viewer'); target element is 'SignalNameBox' (Name='TreeViewTimeTextBox'); target property is 'Height' (type 'Double')
System.Windows.Data Error: 39 : BindingExpression path error: 'GraphHeight' property not found on 'object' ''UserControl' (Name='graph_viewer')'. BindingExpression:Path=GraphHeight; DataItem='UserControl' (Name='graph_viewer'); target element is 'SignalGraphAxis' (Name='signal_axis'); target property is 'GraphHeight' (type 'Int32')
System.Windows.Data Error: 39 : BindingExpression path error: '_SignalDataViewModel' property not found on 'object' ''UserControl' (Name='graph_viewer')'. BindingExpression:Path=_SignalDataViewModel.MaxTimeValue; DataItem='UserControl' (Name='graph_viewer'); target element is 'SignalGraphAxis' (Name='signal_axis'); target property is 'MaxTimeValue' (type 'Int32')
share|improve this question
    
Try to replace Binding on TemplateBinding. It helped? –  Anatoliy Nikolaev Jul 12 '13 at 21:39

1 Answer 1

up vote 2 down vote accepted

I'm pretty sure you can't use ElementName to reference an element outside of a control template. (Although I can't find documentation to that effect right now.) Even if you could, it doesn't really make sense -- you're attempting to write a style that contains a hidden dependency, which will introduce potential runtime errors.

An alternate approach would be to add a dependency property to the control. Write a class that extends TreeView, and give it a DP named SignalNameBoxHeight or similar. 

public class ExtendedTreeView : TreeView
{
    public double SignalNameBoxHeight
    {
        get { return (double)GetValue(SignalNameBoxHeightProperty ); }
        set { SetValue(SignalNameBoxHeightProperty, value); }
    }

    public static readonly DependencyProperty SignalNameBoxHeightProperty =
        DependencyProperty.Register("SignalNameBoxHeight", 
        typeof(double), 
        typeof(ExtendedTreeView), 
        null);

    public ExtendedTreeView ()
    {
        this.DefaultStyleKey = typeof(Treeview);
    }
}

Then you can use TemplateBinding inside the control template to set the property:

<wpfExp:SignalNameBox
    `Height="{TemplateBinding SignalNameBoxHeight}"`
/>

All that's left is for consumers of your style to provide the binding source:

<my:ExtendedTreeView 
    SignalNameBoxHeight="{Binding ElementName=graph_viewer, Path=GraphHeight}" />

Edit

It looks like you could use FindAncestor to reference an element outside a control template:

{RelativeSource FindAncestor} is mainly used in control templates or predictable self-contained UI compositions, for cases where a control is always expected to be in a visual tree of a certain ancestor type.

The limitation of course is that this is only possible for ancestors of the control, not siblings.

share|improve this answer
    
I guess it makes sense why i can't reference an outside element from the style, but if i put the binding in the control template for a specific treeview rather than a style, it still doesn't bind, and it seems reasonable to bind a specific treeview's template to another control –  James Joshua Street Jul 12 '13 at 21:50
    
@JamesJoshuaStreet I see your point, and it looks like I was at minimum half wrong -- you could use a RelativeSource with FindAncestor binding (see my update above). –  McGarnagle Jul 12 '13 at 21:58
    
yeah, well despite everything even relativesource with findancestor is not binding correctly. This only happens at design time though, so I don't know what is going on –  James Joshua Street Jul 12 '13 at 22:09
    
I am so tempted to just ignore the designer and go back to coding stuff that is actually relevant; but i figure learning how the designer works might be useful someday. –  James Joshua Street Jul 12 '13 at 22:10
    
The designer is useful for sure, but it's really flaky. –  McGarnagle Jul 12 '13 at 22:12

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