What does Binding="{Binding (0)}" mean?

Question

I found this:

<DataTrigger Value="True" Binding="{Binding (0)}">

triggers in RibbonMenuButton template. What does it mean? I've tried to google, but found nothing.

UPD more code:

<ControlTemplate x:Key="RibbonMenuButtonControlTemplate1" TargetType="{x:Type RibbonMenuButton}">
...
    <DataTrigger Binding="{Binding (0)}" Value="True">
        <Setter Property="TextElement.Foreground" TargetName="MainGrid" Value="{DynamicResource {x:Static SystemColors.MenuTextBrushKey}}"/>
        <Setter Property="PathFill" TargetName="TwoLineText" Value="{DynamicResource {x:Static SystemColors.MenuTextBrushKey}}"/>
        <Setter Property="CornerRadius" TargetName="OuterBorder" Value="0"/>
        <Setter Property="Background" TargetName="OuterBorder" Value="Transparent"/>
        <Setter Property="BorderBrush" TargetName="OuterBorder" Value="Transparent"/>
    </DataTrigger>
...

This code created in Blend after "edit template" button pressed on RibbonMenuButton control.

Answer 1

It looks like a bug. As far as I know, in WPF can not be Binding of this type. Below is a list of deficiencies, please pay attention to the first paragraph, quoted from connect.microsoft.com (archive):

I'm trying to style the ribbon control (System.Windows.Controls.Ribbon) and I keep running into problems.

• If I use Blend or another tool to copy the default template of the Ribbon, the RibbonGroup, the RibbonTab, etc. these templates have errors. There are Bindings like {Binding (0)}.

• I cannot change the height of the ribbon control.

• It's not possible to change the template of the RibbonGroup, to change the appearance of the separator and to place the header in the top left corner of the group.

• It's not possible to add a label to the ApplicationMenuButton. Furthermore this button has a fixed width.

• I can't manage to remove the borders at the bottom of the ribbon control.

As I understand it, there is no hotfix.

Answer 2

The only time this can appear is in the tokenized path format. See the code examples under "Indirect Targeting" in the Storyboards Overview. In XAML code, however, it's invalid. I imagine what happened was something like this:

// something goes wrong here, and GetProperties returns an empty array
var propertyChain = GetProperties();

var path = new PropertyPath("(0)", propertyChain);

trigger.Binding = new Binding { Path = path };

With an empty PathParameters, the XAML generator might then dump the raw tokenized path.

Answer 3

Sorry for placing this as answer but it doesnt fit in a comment.

Its still too less context you gave to us, however here is my guess.

Its a placeholder for something. Placeholders are rare in wpf world but usefull. That is all that I can think of right now with the information you gave to us. Its the only thing that makes sense to me.

I have seen few placeholders. Its a smart idea.

Usually if you have many different themes with different resource names you will end up creating such placeholders which will complete xaml file at pre or post build time.

Means you hit build action and after or before it compiles the xaml files will get combined and a tool provided by guys who wrote that ribbonbar will be executed to inject proper theme resource names instead of placeholders.

Anything could be placed instead of placeholders...

Where did you get that code from anyways? Can you use Snoop tool to see what is DataContext?

Provide us with more context please.

I would suggest you to dump the template in a file at runtime and then you will know what is going on.

Here is how:

var stringBuilder = new StringBuilder();
var xmlSettings = new XmlWriterSettings
{
  Indent = true
};

using (var xmlWriter = XmlWriter.Create(stringBuilder, xmlSettings))
{
  XamlWriter.Save(controlName.Template, xmlWriter);
}

If there is no (0) anymore in the template you dumped in a file at runtime then you will know its a f***ing placeholder. :) :) :)

Could you please test this out and let us know.