AvaloniaUI/Avalonia · error · NotSupportedException

TemplatedParentNode is invalid in conjunction with a binding

Error message

TemplatedParentNode is invalid in conjunction with a binding source.

What it means

TemplatedParentNode.SelectSource throws NotSupportedException when an explicit binding source is set together with a $templatedParent relative source. The templated parent is resolved from the target's StyledElement.TemplatedParent, so specifying an explicit Source is contradictory and disallowed.

Source

Thrown at src/Avalonia.Base/Data/Core/ExpressionNodes/TemplatedParentNode.cs:16

using System;
using System.Text;

namespace Avalonia.Data.Core.ExpressionNodes;

internal sealed class TemplatedParentNode : SourceNode
{
    public override void BuildString(StringBuilder builder)
    {         
        builder.Append("$templatedParent");
    }

    public override object? SelectSource(object? source, object target, object? anchor)
    {
        if (source != AvaloniaProperty.UnsetValue)
            throw new NotSupportedException(
                "TemplatedParentNode is invalid in conjunction with a binding source.");
        if (target is StyledElement)
            return target;
        if (anchor is StyledElement)
            return anchor;
        throw new InvalidOperationException("Cannot find a StyledElement to get a TemplatedParent.");
    }

    protected override void OnSourceChanged(object? source, Exception? dataValidationError)
    {
        if (!ValidateNonNullSource(source))
            return;

        if (source is StyledElement newElement)
        {
            newElement.PropertyChanged += OnPropertyChanged;
            SetValue(newElement.TemplatedParent);
        }

View on GitHub (pinned to 11c5427268)

Solutions

1. Remove the explicit Source so the binding resolves TemplatedParent from the target StyledElement.
2. If a fixed source is required, drop $templatedParent and bind the source object directly.

Example fix

// before
{Binding $templatedParent.Foreground, Source={StaticResource x}}
// after
{Binding $templatedParent.Foreground}

// TemplatedParent RelativeSource and explicit Source are mutually exclusive.
bool UsesTemplatedParent(Binding b) =>
    b.RelativeSource is RelativeSource rs && rs.Mode == RelativeSourceMode.TemplatedParent;

if (UsesTemplatedParent(binding) && binding.Source is not null)
    throw new InvalidOperationException("Cannot combine TemplatedParent with Source.");

try { target.Bind(prop, binding); }
catch (NotSupportedException ex) when (ex.Message.Contains("TemplatedParentNode"))
{ /* drop Source for templated-parent bindings */ }

When it happens

Trigger: Setting Binding.Source (or another source descriptor) on a binding whose path begins with $templatedParent, typically inside a ControlTemplate.

Common situations: Adding Source= to a template binding; mixing RelativeSource={RelativeSource TemplatedParent} with an explicit Source on the same binding.

Related errors

• Cannot find a StyledElement to get a TemplatedParent.
• DataContextNode is invalid in conjunction with a binding sou
• LogicalAncestorNode is invalid in conjunction with a binding
• Cannot find an ILogical to get a logical ancestor.
• Cannot find an ILogical to get a visual ancestor.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/a8f7678b817db356. Report an issue: GitHub.