Widget `on_update` method is already registered!

Error message

Widget {node_handle} `on_update` method is already registered!

What it means

During widget registration the registry inserts the node handle into the on_update set when the widget's need_update flag is true. Inserting an already-present handle means the same widget is registered twice, producing this warning. It flags duplicate registration of an updatable widget; the registry prevents double updates but the call site has a bug.

Solutions

Register each widget exactly once; audit the add-node path for double calls.
Always pair register with unregister on widget removal so handles don't persist in the on_update set.
Add a registration guard/flag around repeated UI rebuilds.
If harmless in your flow, the warning can be tolerated, but fix the duplicate to avoid future routing bugs.

Example fix

// before
let widget = MyWidgetBuilder::new(...).build(ctx);
ui.register(widget.clone());
ui.register(widget); // duplicate
// after
let widget = MyWidgetBuilder::new(...).build(ctx);
ui.register(widget); // single registration

Defensive patterns

Strategy: validation

Validate before calling

let newly = self.registered_update_handles.insert(node.handle());
if newly { ui.register_widget(node); }

Prevention

Ensure each updatable widget is registered exactly once.
Unregister on remove so the on_update set stays consistent.
Centralize UI registration in one function to avoid scattered duplicate calls.
On UI rebuild, reset registry state alongside widget handles.

When it happens

Trigger: Calling WidgetMethodsRegistry::register (via the UI node registration flow) twice for a widget whose Control::need_update is true — e.g. re-inserting a node, builder double-registration, or plugin reload re-registering without unregistering.

Common situations: Widgets with per-frame update logic (Control::on_update) added to the UI twice; re-registering after a remove that skipped unregister; game code rebuilding UI without cleaning registry state.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of FyroxEngine/Fyrox@76c91aad8e (2026-09-10). Data as JSON: /api/errors/20a1c160960c9106. Report an issue: GitHub.

Appendix: source

Thrown at fyrox-ui/src/lib.rs:673

    handle_os_event: FxHashSet<Handle<UiNode>>,
}

impl WidgetMethodsRegistry {
    fn register<T: Control + ?Sized>(&mut self, node: &T) {
        let node_handle = node.handle();

        if node.preview_messages && !self.preview_message.insert(node_handle) {
            Log::warn(format!(
                "Widget {node_handle} `preview_message` method is already registered!"
            ));
        }
        if node.handle_os_events && !self.handle_os_event.insert(node_handle) {
            Log::warn(format!(
                "Widget {node_handle} `handle_os_event` method is already registered!"
            ));
        }
        if node.need_update && !self.on_update.insert(node_handle) {
            Log::warn(format!(
                "Widget {node_handle} `on_update` method is already registered!"
            ));
        }
    }

    fn unregister<T: Control + ?Sized>(&mut self, node: &T) {
        let node_handle = node.handle();

        self.preview_message.remove(&node_handle);
        self.on_update.remove(&node_handle);
        self.handle_os_event.remove(&node_handle);
    }
}

/// A set of switches that allows you to disable a particular step of UI update pipeline.
#[derive(Clone, PartialEq, Eq, Default)]
pub struct UiUpdateSwitches {
    /// A set of nodes that will be updated, everything else won't be updated.

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