dotnet/wpf · error · ArgumentException

SR.Verify_AreNotEqual

Error message

SR.Verify_AreNotEqual

What it means

Verify.AreNotEqual<T>(notExpected, actual, parameterName) throws ArgumentException(SR.Verify_AreNotEqual, parameterName) when actual equals the forbidden value. This branch handles notExpected == null: two nulls are considered equal, so actual must be non-null (and not 'equal' to null in the type's semantics). The formatted message includes the disallowed value.

Solutions

1. Look at parameterName in the exception to find the argument; ensure it is not the forbidden value before the call.
2. Add an explicit guard: if (Equals(actual, notExpected)) throw with a domain-specific message.
3. Substitute a valid non-null value or default for the argument.

Example fix

// before
Verify.AreNotEqual(null, value, nameof(value)); // value == null -> ArgumentException
// after
if (value == null) value = FallbackValue;
Verify.AreNotEqual(null, value, nameof(value));

if (actual is null)
    throw new ArgumentNullException(nameof(actual), "null is not an allowed value here.");

bool IsAllowedValue<T>(T actual, T forbidden) where T : notnull => !forbidden.Equals(actual);

try
{
    LibraryCall(actual);
}
catch (ArgumentException ex) when (ex.ParamName == "actual")
{
    logger.LogError("Argument {Param} must not equal the forbidden value", ex.ParamName);
    throw;
}

When it happens

Trigger: Calling an API whose wrapper calls Verify.AreNotEqual(null, actual, name) while passing null (or a value whose Equals(null) is true) for that parameter.

Common situations: Passing null to parameters that must be non-null under value semantics; default(T) for a struct/class leaking in as the forbidden value; deserialized objects with null fields used as arguments.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• ' ' is not a valid value for ' '.
• ArgumentException(message, name)
• ArgumentNullException(name)
• ArgumentOutOfRangeException(authentication)
• ArgumentOutOfRangeException

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/9871e02789c59e06. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/WindowsBase/MS/Internal/Verify.cs:96

                throw new ArgumentException(message, name);
            }
        }

        /// <summary>
        /// Verifies two values are not equal to each other.  Throws an ArgumentException if they are.
        /// </summary>
        /// <param name="actual">The actual value.</param>
        /// <param name="notExpected">The value that 'actual' should not be.</param>
        /// <param name="parameterName">The name to display for 'actual' in the exception if this test fails.</param>
        /// <param name="message">The message to include in the ArgumentException.</param>
        public static void AreNotEqual<T>(T actual, T notExpected, string parameterName, string message)
        {
            if (notExpected == null)
            {
                // Two nulls are considered equal, regardless of type semantics.
                if (actual == null || actual.Equals(notExpected))
                {
                    throw new ArgumentException(SR.Format(SR.Verify_AreNotEqual, notExpected), parameterName);
                }
            }
            else if (notExpected.Equals(actual))
            {
                throw new ArgumentException(SR.Format(SR.Verify_AreNotEqual, notExpected), parameterName);
            }
        }

        /// <summary>
        /// Verifies the specified file exists.  Throws an ArgumentException if it doesn't.
        /// </summary>
        /// <param name="filePath">The file path to check for existence.</param>
        /// <param name="parameterName">Name of the parameter to include in the ArgumentException.</param>
        /// <remarks>This method demands FileIOPermission(FileIOPermissionAccess.PathDiscovery)</remarks>
        public static void FileExists(string filePath, string parameterName)
        {
            Verify.IsNeitherNullNorEmpty(filePath, parameterName);

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