slint-ui/slint · error

Cannot show component

Error message

Cannot show component: {err}

What it means

ComponentInstance::show failed after build_and_show successfully created the preview component instance on the existing window. Showing the instance makes it the visible content of the remote-viewer window; a failure here means the runtime could not present the component (window/backend rejection), and it is treated as an unrecoverable anyhow error.

Solutions

1. Retry via show_current so the placeholder is reinstalled and the component is re-created and shown from scratch.
2. Verify the window and platform event loop are still alive at swap time; guard the swap against concurrent teardown.
3. Update editor and viewer to matching slint versions to rule out runtime incompatibilities.
4. Read the inner error from new_instance.show() to identify the platform/backend cause and fix the window setup.

match new_instance.show() {
    Ok(()) => { *user_instance = Some(new_instance); },
    Err(err) => {
        // window/backend refused the show; fall back to the placeholder
        tracing::error!("Cannot show component: {err}");
        let _ = swap_to_placeholder(placeholder, user_instance, chrome, "Preview failed", RemoteViewerState::PreviewError);
    }
}

When it happens

Trigger: new_instance.show() returns Err after create_with_existing_window succeeded in build_and_show — the window backend refuses to show the freshly swapped-in component (window already closing, platform event-loop failure, renderer unavailable).

Common situations: User disconnects or the device window is destroyed during the swap; embedded platform backend cannot show a second component on the same window; slint runtime/platform initialization problems on the target device.

Related errors

• Cannot create component instance
• Cannot create placeholder
• Cannot show placeholder
• First argument not an array
• Second argument not an integer

AI-assisted analysis of slint-ui/slint@bb937076de (2026-09-16). Data as JSON: /api/errors/895ef5cecc80859f. Report an issue: GitHub.

Appendix: source

Thrown at tools/viewer/remote.rs:411

        }
        PreviewCompilation::ComponentNotFound => {
            swap_to_placeholder(
                placeholder,
                user_instance,
                chrome,
                "Component not found",
                RemoteViewerState::PreviewError,
            )?;
            return Ok(());
        }
        PreviewCompilation::Unavailable => return Ok(()),
    };

    let new_instance = component
        .create_with_existing_window(placeholder.window())
        .map_err(|err| anyhow::anyhow!("Cannot create component instance: {err}"))?;

    new_instance.show().map_err(|err| anyhow::anyhow!("Cannot show component: {err}"))?;
    *user_instance = Some(new_instance);
    // The placeholder is hidden now, but keep its state property truthful.
    placeholder.set_state(RemoteViewerState::Previewing);
    Ok(())
}

/// Everything on the placeholder screen that doesn't depend on what the
/// connection is doing.
///
/// [`swap_to_placeholder`] builds a whole new window each time, so anything
/// missing from [`Chrome::apply`] silently disappears the first time the
/// preview is swapped out.
struct Chrome {
    /// Newline-separated `ip:port` list the editor can be pointed at.
    address: String,
    /// Friendly device name. Bonjour can rename us on iOS resume, so this
    /// isn't fixed for the life of the process.
    name: String,

View on GitHub (pinned to bb937076de)