AvaloniaUI/Avalonia · error · InvalidOperationException

Cannot get system name for {Kind} format {Identifier}

Error message

Cannot get system name for {Kind} format {Identifier}

What it means

ToSystemName produces the platform-facing string for a DataFormat. Only Application (prefix + identifier) and Platform (raw identifier) kinds have a meaningful system name; Universal and InProcess formats do not map to a platform string, so the method throws InvalidOperationException for them.

Source

Thrown at src/Avalonia.Base/Input/DataFormat.cs:65

    /// <summary>
    /// Creates a name for this format, usable by the underlying platform.
    /// </summary>
    /// <param name="applicationPrefix">The system prefix used to recognize the name as an application format.</param>
    /// <returns>A system name for the format.</returns>
    /// <remarks>
    /// This method can only be called if <see cref="Kind"/> is
    /// <see cref="DataFormatKind.Application"/> or <see cref="DataFormatKind.Platform"/>.
    /// </remarks>
    public string ToSystemName(string applicationPrefix)
    {
        ThrowHelper.ThrowIfNull(applicationPrefix);

        return Kind switch
        {
            DataFormatKind.Application => applicationPrefix + Identifier,
            DataFormatKind.Platform => Identifier,
            _ => throw new InvalidOperationException($"Cannot get system name for {Kind} format {Identifier}")
        };
    }

    /// <inheritdoc />
    public bool Equals(DataFormat? other)
    {
        if (other is null)
            return false;
        if (ReferenceEquals(this, other))
            return true;
        return Kind == other.Kind && Identifier == other.Identifier;
    }

    /// <inheritdoc />
    public override bool Equals(object? obj)
        => Equals(obj as DataFormat);

    /// <inheritdoc />

View on GitHub (pinned to 11c5427268)

Solutions

1. Only call ToSystemName on Application or Platform formats.
2. For Universal formats, use the platform's built-in text/file/bitmap handling rather than a custom system name.
3. Guard on Kind before calling: `if (format.Kind is Application or Platform) ...`.

Example fix

// before:
var name = DataFormat.Text.ToSystemName("myapp:"); // Universal -> throws

// after:
string name = format.Kind switch
{
    DataFormatKind.Application => format.ToSystemName("myapp:"),
    DataFormatKind.Platform   => format.ToSystemName("myapp:"),
    _ => throw new InvalidOperationException($"No system name for {format.Kind}")
};

if (format.Kind is not (DataFormatKind.Application or DataFormatKind.Platform))
    throw new InvalidOperationException($"No system name for {format.Kind}.");
var name = format.ToSystemName(prefix);

static bool HasSystemName(DataFormat f) => f.Kind is DataFormatKind.Application or DataFormatKind.Platform;

When it happens

Trigger: Calling `format.ToSystemName(prefix)` on a DataFormat whose Kind is Universal (e.g. DataFormat.Text/Bitmap/File) or InProcess (created via CreateInProcessFormat<T>).

Common situations: Passing the built-in DataFormat.Text/DataFormat.File to a clipboard/drag-drop routine that calls ToSystemName. Trying to get a system name for an in-process-only format.

Related errors

• Invalid application identifier
• Cannot determine visual parent.
• BindingExpression has not been started.
• Cannot call AsObservable on a to binding expression which is
• BindingExpression was already attached.

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/6088482a5f2e2b27. Report an issue: GitHub.