mgth/LittleBigMouse · error · Exception

No window found

Error message

No window found

What it means

MainWindowManager.Show resolves the view for a view-model through mvvmService.MainContext.GetView<DefaultViewMode> and converts it to a window via AsWindow(). When the view is null or AsWindow() yields null (the MVVM context has no registered view/template for that view-model), a plain Exception('No window found') is thrown instead of silently returning.

Solutions

1. Verify the view class for this view-model exists, implements IDefaultViewClass, and is registered with the MVVM context (DataTemplates / locator) before calling Show.
2. Ensure the assembly containing the view is loaded and scanned by the mvvmService before Show is invoked.
3. Pass the correct view-model instance produced by the app's navigation/service layer, not an ad-hoc instance whose type has no registered view.
4. Wrap the call and fall back to creating the DefaultWindow manually if the resolver returns null.

Example fix

// before
_manager.Show(viewModel); // throws 'No window found' if view unregistered
// after
var view = mvvmService.MainContext.GetView<DefaultViewMode>(viewModel, typeof(IDefaultViewClass));
if (view?.AsWindow() is null)
    _logger.Warn("No registered view for {Vm}; skipping window show", viewModel.GetType().Name);
else
    _manager.Show(viewModel);

// before calling Show
var probe = mvvmService.MainContext.GetView<DefaultViewMode>(viewModel, typeof(IDefaultViewClass));
if (probe?.AsWindow() is null)
    throw new InvalidOperationException(
        $"No view registered for {viewModel.GetType().Name}; check DataTemplates/locator registration");

bool HasRegisteredWindow(object viewModel, IMvvmService mvvm) =>
    mvvm.MainContext
        .GetView<DefaultViewMode>(viewModel, typeof(IDefaultViewClass))
        ?.AsWindow() is not null;

try { mainWindowManager.Show(viewModel); }
catch (Exception ex) when (ex.Message == "No window found")
{ _logger.Error("View for {Vm} is not registered", viewModel.GetType().Name); /* skip or fall back */ }

When it happens

Trigger: Calling Show(viewModel) when no view is registered for the view-model type under DefaultViewMode/IDefaultViewClass — e.g. the view assembly was not loaded, the view-model was constructed manually without the matching view registration, or AsWindow() cannot convert the resolved view to a Window.

Common situations: A plugin or DI refactor removed/renamed the view registration; launching a UI surface (e.g. main window) before the Avalonia view locator is initialized; asking for a window type whose class does not implement IDefaultViewClass; headless/CI environment where views fail to materialize.

Understand the failure class

Background: "Not found" and "does not exist" errors: why "Task not found", "No such folder", and "Can't find" fire when a lookup comes back empty — this error's family across 14 libraries.

AI-assisted analysis of mgth/LittleBigMouse@7a42f01d47 (2026-09-16). Data as JSON: /api/errors/4ab7d38ccfbf30aa. Report an issue: GitHub.

Appendix: source

Thrown at LittleBigMouse.Ui/LittleBigMouse.Ui.Avalonia/Main/MainWindowManager.cs:67

    public void Show(IMainService mainService, Func<Window, Task<bool>> confirmClose)
    {
        if (_window?.IsLoaded == true)
        {
            _window.WindowState = WindowState.Normal;
            _window.Activate();
            return;
        }

        var viewModel = viewModelLocator();
        viewModel.MainService = mainService;

        _plugins?.Invoke(viewModel);

        var view = mvvmService
            .MainContext
            .GetView<DefaultViewMode>(viewModel, typeof(IDefaultViewClass));

        var window = view?.AsWindow() ?? throw new Exception("No window found");

        // AsWindow() creates a bare DefaultWindow with no size: restore the last
        // session's geometry (or a sensible default) and save it back on close.
        MainWindowGeometry.Attach(window);

        var subscriptions = new CompositeDisposable();
        var closeConfirmed = false;

        void OnClosed(object? sender, EventArgs e)
        {
            _window = null;
            ReleaseWindowSubscriptions();
        }

        async void OnClosing(object? sender, WindowClosingEventArgs e)
        {
            if (closeConfirmed || sender is not Window closing) return;

View on GitHub (pinned to 7a42f01d47)