// Copy normals.
foreach (int textureIndex in f.TextureIndices)
{
        TextureCoordinate tc = wavefrontObject.Textures[textureIndex];
        mesh.TextureCoordinates.Add(new Point3D(tc.U, tc.V, tc.W));
}

// Copy normals.
foreach (int textureIndex in f.TextureIndices) 
{
    if (wavefrontObject.Textures.Count > 0) 
    {
          TextureCoordinate tc = wavefrontObject.Textures[textureIndex];
           mesh.TextureCoordinates.Add(new Point3D(tc.U, tc.V, tc.W));
    }
}

    private void ParseLine( int vertexCount ) {
        // Fix: explicitly set the array length
        string[] rawFaces = new string[3];

        vindices = new int[vertexCount];
        nindices = new int[vertexCount];
        tindices = new int[vertexCount];
        vertices = new Vertex[vertexCount];
        normals = new Vertex[vertexCount];
        textures = new TextureCoordinate[vertexCount];

        for ( int i = 1; i <= vertexCount; i++ ) {
            // Fix: Use additional array for parsed words
            var wordParts = Words[i].Split('/');
            // Fix: setup rawFaces array
            rawFaces[0] = wordParts[0];
            rawFaces[1] = wordParts.Length == 3 ? wordParts[1] : null;
            rawFaces[2] = wordParts.Length == 3 
                ? wordParts[2] 
                : wordParts.Length == 2 
                    ? wordParts[1]
                    : null
            ;

            // v
            int currentValue = int.Parse(rawFaces[0]);
            vindices[i - 1] = currentValue - 1;
            // save vertex
            vertices[i - 1] = _object.Vertices[currentValue - 1];   // -1 because references starts at 1

            if ( wordParts.Length == 1 ) {
                continue;
            }

            // save texcoords. 
            if ( !string.IsNullOrEmpty(rawFaces[1]) ) {
                currentValue = int.Parse(rawFaces[1]);
                // This is to compensate the fact that if no texture is in the obj file, 
                // sometimes '1' is put instead of 'blank' (we find coord1/1/coord3 instead of 
                // coord1//coord3 or coord1/coord3)                 
                if (currentValue <= _object.Textures.Count) {
                    tindices[i - 1] = currentValue - 1;
                    textures[i - 1] = _object.Textures[currentValue - 1]; // -1 because references starts at 1
                }
            }

            // save normal
            currentValue = int.Parse(rawFaces[2]);

            nindices[i - 1] = currentValue - 1;
            normals[i - 1] = _object.Normals[currentValue - 1];     // -1 because references starts at 1
        }
    }

usemtl material-ref 

# start test file
mtllib ./mylib.mtl
usemtl red
# end test file

    public override void IncorporateResults(WavefrontObject wavefrontObject) {
        if (!wavefrontObject.Materials.ContainsKey(_materialName))
            return;

        Material newMaterial = wavefrontObject.Materials[_materialName];

        // Fix: CurrentGroup could be null...
        if ( wavefrontObject.CurrentGroup == null ) {
            wavefrontObject.CurrentGroup = new Group("default");
        }
        wavefrontObject.CurrentGroup.Material = newMaterial;
    }