dotnet/wpf · error · ArgumentException

The URI must be absolute.

Error message

The URI must be absolute.

What it means

Verify.UriIsAbsolute first asserts the Uri is non-null, then asserts uri.IsAbsoluteUri is true, throwing ArgumentException('The URI must be absolute.', parameterName) for relative URIs like 'page.xaml' or '/path'. Many WPF/interop APIs need scheme+host information that only absolute URIs carry.

Solutions

  1. Ensure the Uri is created with UriKind.Absolute and includes scheme (http://, pack://application:,,,/, file:///).
  2. Resolve relative URIs against a known base before the call: new Uri(new Uri(baseUri), relative).
  3. For WPF resources, use pack URIs (pack://application:,,,/Assembly;component/path) to make them absolute.
  4. Validate with uri.IsAbsoluteUri yourself first and give the user a clear error message.

Example fix

// before
var uri = new Uri("images/logo.png", UriKind.Relative);
Verify.UriIsAbsolute(uri, nameof(uri));
// after
var uri = new Uri(new Uri("pack://application:,,,/MyApp;component/"), "images/logo.png");
Verify.UriIsAbsolute(uri, nameof(uri));
Defensive patterns

Strategy: validation

Validate before calling

if (uri == null || !uri.IsAbsoluteUri)
    throw new ArgumentException("A absolute URI is required", nameof(uri));
Verify.UriIsAbsolute(uri, nameof(uri));

Type guard

static bool IsAbsoluteUri(Uri uri) => uri is not null && uri.IsAbsoluteUri;

Try / catch

try {
    Verify.UriIsAbsolute(uri, nameof(uri));
} catch (ArgumentException ex) when (ex.ParamName == nameof(uri)) {
    uri = new Uri(new Uri(AppContext.BaseDirectory), originalRelative);
}

Prevention

When it happens

Trigger: Calling Verify.UriIsAbsolute(uri, parameterName) (or APIs that use it, e.g. navigation/pack URI helpers) with a relative Uri such as new Uri("images/pic.png", UriKind.Relative) or a relative string parsed via Uri.TryCreate with UriKind.RelativeOrRelative-only.

Common situations: Config/app settings storing relative paths; user-supplied URLs lacking a scheme; code that builds Uri without UriKind.Absolute; switching environments where a base URL was dropped.

Understand the failure class

Background: "Invalid URL" errors: why new URL(), URI.parse, and reqwest::Url reject your string — missing scheme, whitespace, and bad path format — this error's family across 39 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/553ff90e40ce1099. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Standard/Verify.cs:220

                // Two nulls are considered equal, regardless of type semantics.
                if (null == actual || actual.Equals(notExpected))
                {
                    throw new ArgumentException(message, parameterName);
                }
            }
            else if (notExpected.Equals(actual))
            {
                throw new ArgumentException(message, parameterName);
            }
        }
        
        [DebuggerStepThrough]
        public static void UriIsAbsolute(Uri uri, string parameterName)
        {
            Verify.IsNotNull(uri, parameterName);
            if (!uri.IsAbsoluteUri)
            {
                throw new ArgumentException("The URI must be absolute.", parameterName);
            }
        }

        /// <summary>
        /// Verifies that the specified value is within the expected range.  The assertion fails if it isn't.
        /// </summary>
        /// <param name="lowerBoundInclusive">The lower bound inclusive value.</param>
        /// <param name="value">The value to verify.</param>
        /// <param name="upperBoundExclusive">The upper bound exclusive value.</param>      
        [DebuggerStepThrough]
        public static void BoundedInteger(int lowerBoundInclusive, int value, int upperBoundExclusive, string parameterName)
        {
            if (value < lowerBoundInclusive || value >= upperBoundExclusive)
            {
                throw new ArgumentException(string.Create(CultureInfo.InvariantCulture, $"The integer value must be bounded with [{lowerBoundInclusive}, {upperBoundExclusive})"), parameterName);
            }
        }

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