dotnet/wpf · error · ArgumentException

SR.UriNotAbsolute

Error message

SR.UriNotAbsolute

What it means

GlyphTypeface.Initialize (called from the constructor and from ISupportInitialize.EndInit) requires typefaceSource to be an absolute URI (file:///C:/Fonts/segoeui.ttf or pack://...). A relative URI like "fonts/my.ttf" or "segoeui.ttf" leaves the font unresolvable, so the library throws ArgumentException(SR.UriNotAbsolute, nameof(typefaceSource)) immediately.

Solutions

  1. Resolve the font path to an absolute URI before constructing: new GlyphTypeface(new Uri(Path.GetFullPath(fontPath))) or new Uri(fontPath, UriKind.Absolute).
  2. If the path comes from configuration, combine it with AppContext.BaseDirectory: new Uri(Path.Combine(AppContext.BaseDirectory, relativeFontPath)).
  3. Validate with uri.IsAbsoluteUri before calling and surface a clear error otherwise.

Example fix

// before
var typeface = new GlyphTypeface(new Uri("Fonts/segoeui.ttf")); // ArgumentException: UriNotAbsolute

// after
string fontPath = Path.Combine(AppContext.BaseDirectory, "Fonts", "segoeui.ttf");
var typeface = new GlyphTypeface(new Uri(fontPath, UriKind.Absolute));
Defensive patterns

Strategy: validation

Validate before calling

static Uri ToAbsoluteFontUri(string fontPath)
{
    var uri = new Uri(fontPath, UriKind.RelativeOrAbsolute);
    if (!uri.IsAbsoluteUri)
        uri = new Uri(Path.Combine(AppContext.BaseDirectory, fontPath), UriKind.Absolute);
    return uri;
}
// call before: var typeface = new GlyphTypeface(ToAbsoluteFontUri(fontPath));

Type guard

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

Try / catch

try { var typeface = new GlyphTypeface(fontUri); }
catch (ArgumentException ex) when (ex.ParamName == "typefaceSource")
{
    // resolve the configured path against the app base directory and retry once
}

Prevention

When it happens

Trigger: new GlyphTypeface(new Uri("myfont.ttf")) or new GlyphTypeface(new Uri(relativePath, UriKind.Relative)); passing a URI built from a config string that is relative to the app directory; EndInit on a GlyphTypeface whose Source was assigned a relative URI.

Common situations: Loading fonts from config or app settings where only a file name was stored; project files that used relative content paths; copying samples where the font path string happened to be absolute on the sample machine but not yours; Linux/macOS paths without the file:// scheme.

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/798790fc39addd3b. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/GlyphTypeface.cs:116

            _fontFace = new FontFaceLayoutInfo(font);
            _fontSource = new FontSource(typefaceSource);

            Invariant.Assert(  styleSimulations == StyleSimulations.None 
                            || styleSimulations == StyleSimulations.ItalicSimulation 
                            || styleSimulations == StyleSimulations.BoldSimulation
                            || styleSimulations == StyleSimulations.BoldItalicSimulation);
            
            _styleSimulations = styleSimulations;

            _initializationState = InitializationState.IsInitialized; // fully initialized
        }

        private void Initialize(Uri typefaceSource, StyleSimulations styleSimulations)
        {
            ArgumentNullException.ThrowIfNull(typefaceSource);

            if (!typefaceSource.IsAbsoluteUri)
                throw new ArgumentException(SR.UriNotAbsolute, nameof(typefaceSource));

            // remember the original Uri that contains face index
            _originalUri = typefaceSource;

            // split the Uri into the font source Uri and face index
            Uri fontSourceUri;
            int faceIndex;
            Util.SplitFontFaceIndex(typefaceSource, out fontSourceUri, out faceIndex);

            if (   styleSimulations != StyleSimulations.None 
                && styleSimulations != StyleSimulations.ItalicSimulation 
                && styleSimulations != StyleSimulations.BoldSimulation
                && styleSimulations != StyleSimulations.BoldItalicSimulation)
            {
                throw new InvalidEnumArgumentException("styleSimulations", (int)styleSimulations, typeof(StyleSimulations));
            }

            _styleSimulations = styleSimulations;

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