Question

I want to refer to another element, which resides as nested under a custom user control:

<userControls:Test>
     <TextBox Name="Foo" />

     <Button CommandParameter="{Binding Text, ElementName=Foo" Command="{Binding anything}" />
</userControls:Test>

Basically I’m using commands and I’m trying to refer to another element with a name, but I get this famous:

Cannot set Name attribute value ‘…’ on element ‘…’. ‘…’ is under
the scope of element ‘…’, which already had a name registered when
it was defined in another scope.

I figured it’s impossible to name an element: How to create a WPF UserControl with NAMED content

So is there any other way to refer to the element that would work inside nested custom user control content?

Answer 1

I ended up doing it like this:

<UserControl x:Class="MyProject.FooBar"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:userControls="clr-namespace:MyProject.UserControls"
         Loaded="Loaded"> <!-- notice -->

    <userControls:Test>
         <TextBox Initialized="FooInitialized" />

         <Button Initialized="AnotherInitialized" />
    </userControls:Test>

And code:

// This for every initialization, all we do is set names after the elements are initialized.
private void FooInitialized(object sender, EventArgs e)
{
    ((TextBox) sender).Name = "Foo";
}

// Here when the entire junk is loaded, we set the necessary commands.
private void Loaded(object sender, EventArgs e)
{
    // Find elements.
    var button = UIHelper.FindChild<Button>(this, "Bar");
    var textBox = UIHelper.FindChild<TextBox>(this, "Foo");

    // Set up bindings for button.
    button.Command = ((FooViewModel) DataContext).FooCommand;
    button.CommandParameter = textBox;
}

The UIHelper is from https://stackoverflow.com/a/1759923/283055. The button is also given a name the same way as the text box.

Basically all names are set via Initialized event. The only down side is that you must refer to the names in code, and that’s why I’m setting commands via code after the entire component has loaded. I found this the best compromise between code and UI markup.