AvaloniaUI/Avalonia · error · ArgumentException

Invalid application identifier

Error message

Invalid application identifier

What it means

CreateApplicationFormat builds a cross-app-recognizable DataFormat and validates the identifier via IsValidApplicationFormatIdentifier (must be non-empty and contain only valid chars). An invalid identifier is rejected with ArgumentException because the platform name must be parseable/distinguishable.

Source

Thrown at src/Avalonia.Base/Input/DataFormat.cs:161

    /// <typeparam name="T">The data type. Can be any reference type.</typeparam>
    /// <param name="identifier">
    /// The format identifier. This value is only used for equality comparisons within the process
    /// and is never passed to the underlying platform.
    /// </param>
    /// <returns>A new <see cref="DataFormat{T}"/>.</returns>
    public static DataFormat<T> CreateInProcessFormat<T>(string identifier)
        where T : class
    {
        ThrowHelper.ThrowIfNullOrEmpty(identifier);

        return new(DataFormatKind.InProcess, identifier);
    }

    private static DataFormat<T> CreateApplicationFormat<T>(string identifier)
        where T : class
    {
        if (!IsValidApplicationFormatIdentifier(identifier))
            throw new ArgumentException("Invalid application identifier", nameof(identifier));

        return new(DataFormatKind.Application, identifier);
    }

    /// <summary>
    /// Creates a new format for the current platform that returns an array of <see cref="byte"/>.
    /// </summary>
    /// <param name="identifier">
    /// The format identifier. This value is not validated and is passed AS IS to the underlying platform.
    /// Most systems use mime types, but macOS requires Uniform Type Identifiers (UTI).
    /// </param>
    /// <returns>A new <see cref="DataFormat"/>.</returns>
    public static DataFormat<byte[]> CreateBytesPlatformFormat(string identifier)
        => CreatePlatformFormat<byte[]>(identifier);

    /// <summary>
    /// Creates a new format for the current platform that returns a <see cref="string"/>.
    /// </summary>

View on GitHub (pinned to 11c5427268)

Solutions

1. Use a simple identifier of alphanumerics/allowed chars only (typically letters, digits, underscores, dots, hyphens).
2. Sanitize input before creating the format.
3. Validate non-empty first (CreateInProcessFormat already calls ThrowIfNullOrEmpty; for application formats, ensure a clean identifier).

Example fix

// before:
var f = DataFormat.CreateStringApplicationFormat(""); // throws
// or with bad chars:
var f = DataFormat.CreateStringApplicationFormat("my format!"); // throws

// after:
var f = DataFormat.CreateStringApplicationFormat("my-format");

if (!string.IsNullOrEmpty(identifier) && identifier.All(IsValidChar))
    DataFormat.CreateStringApplicationFormat(identifier);

static bool IsValidApplicationId(string s) => !string.IsNullOrEmpty(s) && s.All(IsValidChar); // mirror IsValidApplicationFormatIdentifier

When it happens

Trigger: Calling DataFormat.CreateStringApplicationFormat / CreateBytesApplicationFormat (which route to CreateApplicationFormat) with an empty string or a string containing characters failing IsValidChar (e.g. whitespace, punctuation, or control chars).

Common situations: Generating format identifiers from user input or app metadata that includes disallowed characters. Passing null/empty from a config default.

Related errors

• {nameof(KeySpline)} must have X coordinates >= 0.0 and <= 1.
• Invalid KeySpline X1 value. Must be >= 0.0 and <= 1.0.
• Invalid KeySpline X2 value. Must be >= 0.0 and <= 1.0.
• Cannot get system name for {Kind} format {Identifier}
• Size should be >= (1,1)

AI-assisted analysis of AvaloniaUI/Avalonia@11c5427268 (2026-08-13). Data as JSON: /api/errors/0018b6380daf5ac8. Report an issue: GitHub.