MonoGame/MonoGame · error · ArgumentException

vertexData does not inherit IVertexType

Error message

vertexData does not inherit IVertexType

What it means

Thrown by VertexDeclaration.FromType when the instantiated vertexType object does not implement IVertexType. FromType uses Activator.CreateInstance to build an instance and casts to IVertexType to read VertexDeclaration; if the cast fails (type does not implement the interface), this ArgumentException is thrown.

Source

Thrown at MonoGame.Framework/Graphics/Vertices/VertexDeclaration.cs:218

        /// <returns>The VertexDeclaration.</returns>
        /// <remarks>
        /// Prefer to use VertexDeclarationCache when the declaration lookup
        /// can be performed with a templated type.
        /// </remarks>
		internal static VertexDeclaration FromType([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] Type vertexType)
		{
			if (vertexType == null)
				throw new ArgumentNullException("vertexType", "Cannot be null");

            if (!ReflectionHelpers.IsValueType(vertexType))
            {
				throw new ArgumentException("Must be value type", "vertexType");
			}

            var type = Activator.CreateInstance(vertexType) as IVertexType;
			if (type == null)
			{
				throw new ArgumentException("vertexData does not inherit IVertexType");
			}

            var vertexDeclaration = type.VertexDeclaration;
			if (vertexDeclaration == null)
			{
				throw new Exception("VertexDeclaration cannot be null");
			}

			return vertexDeclaration;
		}

        /// <summary>
        /// Gets a copy of the vertex elements.
        /// </summary>
        /// <returns>A copy of the vertex elements.</returns>
        public VertexElement[] GetVertexElements()
		{
			return (VertexElement[])_data.Elements.Clone();

View on GitHub (pinned to 1d71bbd0ff)

Solutions

1. Implement IVertexType on the vertex struct (provide a public VertexDeclaration property returning the layout).
2. Use a built-in vertex type from Microsoft.Xna.Framework.Graphics (e.g., VertexPositionColor) which already implements IVertexType.
3. Verify the type implements IVertexType via typeof(IVertexType).IsAssignableFrom(vertexType) before calling.

Example fix

// before
public struct MyVertex { public Vector3 Pos; }
var decl = VertexDeclaration.FromType(typeof(MyVertex));
// after
public struct MyVertex : IVertexType {
    public Vector3 Pos;
    public VertexDeclaration VertexDeclaration => ...;
}

if (!typeof(IVertexType).IsAssignableFrom(vertexType))
    throw new ArgumentException($"{vertexType} does not implement IVertexType.");

static bool ImplementsIVertexType(Type t) => typeof(IVertexType).IsAssignableFrom(t);

try { var decl = VertexDeclaration.FromType(vertexType); }
catch (ArgumentException ex) when (ex.Message.Contains("IVertexType"))
{ /* add : IVertexType to the struct and retry */ }

When it happens

Trigger: Passing a struct Type that does not implement IVertexType (no public VertexDeclaration property via the interface). The struct exists and is a value type but lacks the required interface.

Common situations: Defining a custom vertex struct and forgetting ' : IVertexType', or passing a built-in type that is not a vertex type. Note: the parameter name in the message ('vertexData') is a minor doc inconsistency but the cause is the type argument.

Related errors

• VertexDeclaration cannot be null
• Cannot be null
• Must be value type
• Elements cannot be empty
• Type '{newBitmapType}' is not a subclass of BitmapContent.

AI-assisted analysis of MonoGame/MonoGame@1d71bbd0ff (2026-08-13). Data as JSON: /api/errors/7eb7bf45ec81bd70. Report an issue: GitHub.