AvaloniaUI/Avalonia · error · InvalidOperationException

Cannot set Name : styled element already styled.

Error message

Cannot set Name : styled element already styled.

What it means

Error "Cannot set Name : styled element already styled." thrown in AvaloniaUI/Avalonia.

Source

Thrown at src/Avalonia.Base/StyledElement.cs:171

        /// <inheritdoc />
        public event EventHandler? ActualThemeVariantChanged;
        
        /// <summary>
        /// Gets or sets the name of the styled element.
        /// </summary>
        /// <remarks>
        /// An element's name is used to uniquely identify an element within the element's name
        /// scope. Once the element is added to a logical tree, its name cannot be changed.
        /// </remarks>
        public string? Name
        {
            get => _name;

            set
            {
                if (_stylesApplied)
                {
                    throw new InvalidOperationException("Cannot set Name : styled element already styled.");
                }

                _name = value;
            }
        }

        /// <summary>
        /// Gets or sets the styled element's classes.
        /// </summary>
        /// <remarks>
        /// <para>
        /// Classes can be used to apply user-defined styling to styled elements, or to allow styled elements
        /// that share a common purpose to be easily selected.
        /// </para>
        /// </remarks>
        public Classes Classes => _classes ??= new();

        /// <summary>

View on GitHub (pinned to 11c5427268)

Solutions

1. Set the Name property before the element is styled (before it is added to the visual tree and templates are applied).
2. If the name must change at runtime, unregister and re-register it in the appropriate NameScope instead of setting Name directly.

When it happens

Trigger: Raised when the Name property of a styled element is assigned after styling has begun. Defend by setting Name before the element is initialized/added to the tree, and guarding setters against post-init assignment.

Common situations: See trigger scenarios.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/29083c0b629c25b3. Report an issue: GitHub.