FyroxEngine/Fyrox · error

Unknown widget type uuid

Error message

Unknown widget type uuid {id}!

What it means

During scene/widget deserialization, read_widget asks the SerializationContext to create a widget instance from the type UUID stored in the file. If the UUID is not registered (unknown widget type), there is no constructor and the visitor panics.

Solutions

1. Register the missing widget type in the SerializationContext before loading (register all custom widget constructors at startup)
2. Re-save the scene without the unknown widget, then edit the resource file to remove the stale node
3. Restore/upgrade the plugin or crate that defined the widget; check version compatibility between saved assets and engine version

Example fix

// before
let mut ctx = SerializationContext::new();

// after
let mut ctx = SerializationContext::new();
ctx.add::<MyCustomWidget>(MyCustomWidget::type_uuid());

// before loading, verify the type is registered
// serialization_context.try_create(uuid).is_none() => refuse to load with a clear message

// wrap scene loading in catch_unwind or pre-check the file's node type UUIDs against the serialization context

When it happens

Trigger: Loading a UI/scene file saved with a widget type whose registration is missing: custom widget removed or renamed, a plugin not loaded, or type registration order changed between versions.

Common situations: Opening old scenes after deleting or renaming a custom widget; running an editor build without the plugin crate that registers custom widgets; fyrox version upgrade changing engine widget UUIDs.

Related errors

• Animation pool must be empty on load!
• Failed to load brush tool data due to
• Resource manager must be available when deserializing…
• Unable to get a resource of type
• Unable to get a resource of type

AI-assisted analysis of FyroxEngine/Fyrox@76c91aad8e (2026-09-10). Data as JSON: /api/errors/970ee0ca678f8ac7. Report an issue: GitHub.

Appendix: source

Thrown at fyrox-ui/src/node/container.rs:50

/// control over instantiation process at deserialization.
#[derive(Debug, Clone, Default, PartialEq, Reflect)]
#[reflect(type_uuid = "8d572e59-9594-435d-844f-c78cd7696744")]
pub struct WidgetContainer(Option<UiNode>);

fn read_widget(name: &str, visitor: &mut Visitor) -> Result<UiNode, VisitError> {
    let mut region = visitor.enter_region(name)?;

    let mut id = Uuid::default();
    id.visit("TypeUuid", &mut region)?;

    let serialization_context = region
        .blackboard
        .get::<WidgetConstructorContainer>()
        .expect("Visitor environment must contain serialization context!");

    let mut widget = serialization_context
        .try_create(&id)
        .ok_or_else(|| panic!("Unknown widget type uuid {id}!"))
        .unwrap();

    widget.visit("WidgetData", &mut region)?;

    Ok(widget)
}

fn write_widget(name: &str, widget: &mut UiNode, visitor: &mut Visitor) -> VisitResult {
    let mut region = visitor.enter_region(name)?;

    let mut id = widget.id();
    id.visit("TypeUuid", &mut region)?;

    widget.visit("WidgetData", &mut region)?;

    Ok(())
}

View on GitHub (pinned to 76c91aad8e)