What causes "Invalid scheme name: {schemeName}" in tui-cs/Terminal.Gui?

Validate the enum value with Enum.IsDefined(typeof(Schemes), value) before calling GetScheme.

tui-cs/Terminal.Gui · error · ArgumentException

Invalid scheme name

Error message

Invalid scheme name: {schemeName}

What it means

GetScheme(Schemes) converts the enum to its name via SchemesToSchemeName (Enum.GetName). If the enum value is not a defined member (e.g. (Schemes)999 cast from an unchecked int), Enum.GetName returns null and this ArgumentException is thrown.

Solutions

Validate the enum value with Enum.IsDefined(typeof(Schemes), value) before calling GetScheme.
Use a known Schemes member (e.g. Schemes.TopLevel).

Example fix

// before
SchemeManager.GetScheme ((Schemes)999);
// after
Schemes s = (Schemes)999;
if (Enum.IsDefined (typeof (Schemes), s))
{
    SchemeManager.GetScheme (s);
}

Defensive patterns

Strategy: validation

Validate before calling

static bool IsDefinedScheme (Schemes s) => Enum.IsDefined (typeof (Schemes), s);

Try / catch

try { var scheme = SchemeManager.GetScheme (s); }
catch (ArgumentException ex) when (ex.Message.Contains ("Invalid scheme name"))
{ /* s is not a defined Schemes member */ }

Prevention

Always validate enum inputs with Enum.IsDefined before use.
For user-supplied names, prefer the string-based GetScheme/TryGetScheme.

When it happens

Trigger: Calling GetScheme((Schemes)999) or GetScheme((Schemes)(-1)) — an enum value outside the defined Schemes members.

Common situations: Casting an unchecked integer to Schemes; deserializing an invalid numeric scheme id; arithmetic on enum values producing undefined members.

Related errors

AI-assisted analysis of tui-cs/Terminal.Gui@2e47b11478 (2026-08-13). Data as JSON: /api/errors/50b0d9cc37233298. Report an issue: GitHub.

Appendix: source

Thrown at Terminal.Gui/Configuration/SchemeManager.cs:122

        {
            throw new InvalidOperationException ($@"{schemeName}: Does not exist in Schemes.");
        }

        GetSchemes ().Remove (schemeName);
    }

    /// <summary>
    ///     Gets the <see cref="Scheme"/> for the specified <see cref="Drawing.Schemes"/>.
    /// </summary>
    /// <param name="schemeName"></param>
    /// <returns></returns>
    /// <exception cref="ArgumentException"></exception>
    public static Scheme GetScheme (Schemes schemeName)
    {
        // Convert schemeName to string via Enum api
        string? schemeNameString = SchemesToSchemeName (schemeName);

        return schemeNameString is null ? throw new ArgumentException ($"Invalid scheme name: {schemeName}") : GetSchemesForCurrentTheme () [schemeNameString]!;
    }

    /// <summary>
    ///     Gets the <see cref="Scheme"/> for the specified string.
    /// </summary>
    /// <param name="schemeName"></param>
    /// <returns></returns>
    /// <exception cref="KeyNotFoundException">If <paramref name="schemeName"/> is not found in the current theme.</exception>
    public static Scheme GetScheme (string schemeName) => GetSchemesForCurrentTheme () [schemeName]!;

    /// <summary>
    ///     Attempts to get the <see cref="Scheme"/> for the specified name without throwing.
    ///     Returns <see langword="false"/> and sets <paramref name="scheme"/> to <see langword="null"/> if the scheme is
    ///     not found, or if the configuration is not in a state where schemes can be resolved.
    /// </summary>
    /// <param name="schemeName">The name of the scheme to retrieve.</param>
    /// <param name="scheme">
    ///     When this method returns <see langword="true"/>, contains the resolved <see cref="Scheme"/>; otherwise

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