AvaloniaUI/Avalonia · error · NotSupportedException

DataContextNode is invalid in conjunction with a binding sou

Error message

DataContextNode is invalid in conjunction with a binding source.

What it means

DataContextNodeBase.SelectSource throws when a binding source was explicitly provided (source != AvaloniaProperty.UnsetValue) AND the path resolves through $DataContext (or the implicit data-context root). The two are mutually exclusive: a DataContext-relative path reads the inherited DataContext, so an explicit Source contradicts it. The library fails fast instead of silently preferring one.

Source

Thrown at src/Avalonia.Base/Data/Core/ExpressionNodes/DataContextNodeBase.cs:11

using System;
using Avalonia.LogicalTree;

namespace Avalonia.Data.Core.ExpressionNodes;

internal abstract class DataContextNodeBase : SourceNode
{
    public override object? SelectSource(object? source, object target, object? anchor)
    {
        if (source != AvaloniaProperty.UnsetValue)
            throw new NotSupportedException(
                "DataContextNode is invalid in conjunction with a binding source.");
        if (target is IDataContextProvider and AvaloniaObject)
            return target;
        if (anchor is IDataContextProvider and AvaloniaObject)
            return anchor;
        throw new InvalidOperationException("Cannot find a DataContext to bind to.");
    }
}

View on GitHub (pinned to 11c5427268)

Solutions

Remove the explicit Source so the path resolves through DataContext as intended.
If you need an explicit source, change the path so it does not start from DataContext (e.g. use $self or a direct property path on the source object).

Example fix

// before
{Binding Source={StaticResource vm}, Name}
<!-- Name is resolved against DataContext AND a Source is set -->
// after
{Binding Source={StaticResource vm}}
<!-- or -->
{Binding Name}

Defensive patterns

Strategy: validation

Validate before calling

// A DataContext-rooted path and an explicit Source are mutually exclusive.
bool HasExplicitSource(Binding b) =>
    b.Source is not null || b.RelativeSource is not null || !string.IsNullOrEmpty(b.ElementName);

if (IsDataContextRootedPath(path) && HasExplicitSource(binding))
    throw new InvalidOperationException("Cannot set Source on a DataContext-rooted binding.");

Try / catch

try { target.Bind(prop, binding); }
catch (NotSupportedException ex) when (ex.Message.Contains("DataContextNode"))
{ /* remove Source or change the path root */ }

Prevention

Pick exactly one source strategy per binding: DataContext, Source, RelativeSource, or ElementName.
When copying a binding, clear unrelated source fields.
Audit control-template bindings that add Source alongside inherited paths.

When it happens

Trigger: Setting both Binding.Source (or RelativeSource/ElementName) and a path that begins from the data context. Equivalent to mixing a DataContext-rooted compiled binding with an explicit source object.

Common situations: Refactoring a {Binding} to add Source= while leaving the path implicitly DataContext-rooted; combining RelativeSource with a path meant for DataContext; copy-paste from a DataContext binding into a control-template binding without removing the data-context root.

Related errors

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/086e2005346411bc. Report an issue: GitHub.