iced-rs/iced · error

Remove user interface

Error message

Remove user interface

What it means

Panic from `user_interfaces.remove(&id).expect("Remove user interface")` when handling a resize between redraws. Every registered window must have a user interface entry, so a missing entry indicates the window's UI was removed without unregistering the window — an internal invariant violation.

Source

Thrown at winit/src/lib.rs:761

                            continue;
                        };

                        let Some((id, mut window)) = window_manager.get_mut_alias(id) else {
                            continue;
                        };

                        let physical_size = window.state.physical_size();
                        let mut logical_size = window.state.logical_size();

                        if physical_size.width == 0 || physical_size.height == 0 {
                            continue;
                        }

                        // Window was resized between redraws
                        if window.surface_version != window.state.surface_version() {
                            window.renderer.hint(window.state.scale());

                            let ui = user_interfaces.remove(&id).expect("Remove user interface");

                            let layout_span = debug::layout(id);
                            let _ = user_interfaces
                                .insert(id, ui.relayout(logical_size, &mut window.renderer));
                            layout_span.finish();

                            current_compositor.configure_surface(
                                &mut window.surface,
                                physical_size.width,
                                physical_size.height,
                            );

                            window.surface_version = window.state.surface_version();
                        }

                        let redraw_event =
                            core::Event::Window(window::Event::RedrawRequested(Instant::now()));

View on GitHub (pinned to d146509d89)

Solutions

1. Update iced — bookkeeping races between close and redraw have been fixed upstream
2. Avoid closing windows from inside redraw-synchronous code paths
3. If forking, guard the remove with `if let Some(ui)` instead of expect

Example fix

// before
let ui = user_interfaces.remove(&id).expect("Remove user interface");
// after
if let Some(ui) = user_interfaces.remove(&id) { ... }

// application-side: never call window close and rely on redraws for the same id in the same tick

When it happens

Trigger: A RedrawRequested arrives for a window whose user interface was already removed (e.g. window closed during redraw, or ui_caches/interfaces bookkeeping desynced after Close/SetExclusive actions racing the event loop).

Common situations: Rapid window close while a redraw is pending; custom window management via subscription/Action::Close racing redraw events; bugs in forked runtimes.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Get user interface
• Resize surface
• Create window
• Caches must not be empty
• Downcast widget state

AI-assisted analysis of iced-rs/iced@d146509d89 (2026-09-11). Data as JSON: /api/errors/4aec537967be0da6. Report an issue: GitHub.