dotnet/aspnetcore · error · InvalidOperationException

The component type '{componentType}' has a fixed rendermode

Error message

The component type '{componentType}' has a fixed rendermode of '{componentTypeRenderMode}', so it is not valid to specify any rendermode when using this component.

What it means

Thrown by ComponentFactory.InstantiateComponent when a component type has a [RenderMode] attribute (giving it a fixed render mode) AND the call site also specifies a render mode via @rendermode. The framework resolves exactly one render mode; when the type itself declares one, the caller must not supply another. The conflict is detected at ComponentFactory.cs:70-74.

Source

Thrown at src/Components/Components/src/ComponentFactory.cs:74

    public IComponent InstantiateComponent(IServiceProvider serviceProvider, [DynamicallyAccessedMembers(Component)] Type componentType, IComponentRenderMode? callerSpecifiedRenderMode, int? parentComponentId)
    {
        var componentTypeRenderMode = GetComponentTypeRenderMode(componentType);
        IComponent component;

        if (componentTypeRenderMode is null && callerSpecifiedRenderMode is null)
        {
            // Typical case where no rendermode is specified in either location. We don't call ResolveComponentForRenderMode in this case.
            component = _componentActivator.CreateInstance(componentType);
        }
        else
        {
            // At least one rendermode is specified. We require that it's exactly one, and use ResolveComponentForRenderMode with it.
            var effectiveRenderMode = callerSpecifiedRenderMode is null
                ? componentTypeRenderMode!
                : componentTypeRenderMode is null
                    ? callerSpecifiedRenderMode
                    : throw new InvalidOperationException($"The component type '{componentType}' has a fixed rendermode of '{componentTypeRenderMode}', so it is not valid to specify any rendermode when using this component.");
            component = _renderer.ResolveComponentForRenderMode(componentType, parentComponentId, _componentActivator, effectiveRenderMode);
        }

        if (component is null)
        {
            // The default activator/resolver will never do this, but an externally-supplied one might
            throw new InvalidOperationException($"The component activator returned a null value for a component of type {componentType.FullName}.");
        }

        if (!_propertyInjectionDisabled)
        {
            PerformPropertyInjection(serviceProvider, component);
        }

        return component;
    }

    private void PerformPropertyInjection(IServiceProvider serviceProvider, IComponent instance)

View on GitHub (pinned to 294cab2f9b)

Solutions

Remove the @rendermode from the call site — let the component's own [RenderMode] attribute win.
Or remove the [RenderMode] attribute from the component type if callers need to choose.
Do not specify render mode in both places.

Example fix

// before
// Component definition
[RenderMode(InteractiveServer)]
public class MyComponent : ComponentBase { }

// Usage (conflict)
<MyComponent @rendermode="InteractiveWebAssembly" />

// after — remove the caller-side mode
<MyComponent />

Defensive patterns

Strategy: validation

Validate before calling

var typeRenderMode = componentType.GetCustomAttribute<RenderModeAttribute>()?.Mode;
if (typeRenderMode is not null && callerSpecifiedRenderMode is not null)
    throw new InvalidOperationException("Component has a fixed rendermode; do not specify @rendermode at call site.");

Prevention

Choose render mode in one place: either the component attribute or the call site, never both.
Document which components are pinned to a render mode.

When it happens

Trigger: A component decorated with [RenderMode(InteractiveServer)] (or similar) is referenced with an explicit @rendermode="..." in markup. The ternary at line 70-74 throws when neither side is null.

Common situations: Applying [RenderMode] at the component level and also setting @rendermode at the call site; library components that pin their own render mode being used with a caller-specified mode.

Related errors

AI-assisted analysis of dotnet/aspnetcore@294cab2f9b (2026-08-06). Data as JSON: /api/errors/514796de0b3d7cd3. Report an issue: GitHub.