lepoco/wpfui · error · InvalidOperationException

The SnackbarPresenter was never set

Error message

The SnackbarPresenter was never set

What it means

SnackbarService.Show requires a SnackbarPresenter (a content host placed in the visual tree) to display snackbars. Show throws InvalidOperationException if SetSnackbarPresenter was never called, because it needs the presenter to construct and route the Snackbar. The service deliberately fails fast rather than silently dropping the message.

Source

Thrown at src/Wpf.Ui/SnackbarService.cs:45

    /// <inheritdoc />
    public SnackbarPresenter? GetSnackbarPresenter()
    {
        return _presenter;
    }

    /// <inheritdoc />
    public void Show(
        string title,
        string message,
        ControlAppearance appearance,
        IconElement? icon,
        TimeSpan timeout
    )
    {
        if (_presenter is null)
        {
            throw new InvalidOperationException($"The SnackbarPresenter was never set");
        }

        _snackbar ??= new Snackbar(_presenter);

        _snackbar.SetCurrentValue(Snackbar.TitleProperty, title);
        _snackbar.SetCurrentValue(System.Windows.Controls.ContentControl.ContentProperty, message);
        _snackbar.SetCurrentValue(Snackbar.AppearanceProperty, appearance);
        _snackbar.SetCurrentValue(Snackbar.IconProperty, icon);
        _snackbar.SetCurrentValue(
            Snackbar.TimeoutProperty,
            timeout.TotalSeconds == 0 ? DefaultTimeOut : timeout
        );

        _snackbar.Show(true);
    }
}

View on GitHub (pinned to ffebacd610)

Solutions

1. Add a <ui:SnackbarPresenter x:Name="SnackbarPresenter" /> to your main window.
2. In the window's Loaded handler call snackbarService.SetSnackbarPresenter(snackbarPresenter).
3. Defer snackbarService.Show calls until after the presenter has been set.

Example fix

// XAML: <ui:SnackbarPresenter x:Name="RootSnackbar" />

// before
container.GetRequiredService<ISnackbarService>().Show("Hi", "msg", ...); // throws

// after
private void OnLoaded(object sender, RoutedEventArgs e)
{
    var svc = _host.Services.GetRequiredService<ISnackbarService>();
    svc.SetSnackbarPresenter(RootSnackbar);
}

if (snackbarService.GetSnackbarPresenter() is null)
{
    throw new InvalidOperationException("Call SetSnackbarPresenter before showing a snackbar.");
}

static bool IsPresenterReady(ISnackbarService svc) => svc.GetSnackbarPresenter() is not null;

try { snackbarService.Show(title, message, appearance, icon, timeout); }
catch (InvalidOperationException ex) when (ex.Message.Contains("SnackbarPresenter was never set"))
{
    _logger.LogError(ex, "SnackbarPresenter not configured; cannot show snackbar.");
}

When it happens

Trigger: Calling snackbarService.Show(...) before calling snackbarService.SetSnackbarPresenter(...); the presenter host was never added to the window's XAML; the service was constructed but never wired to a presenter.

Common situations: Initialising ISnackbarService via the host/container but forgetting to place a SnackbarPresenter in the main window and call SetSnackbarPresenter in the window's Loaded handler; injecting the service into a view-model and calling Show at startup before the window is ready.

Related errors

• Unable to find the base directory of the application.
• Unable to determine the window source.
• Cannot change DialogHostEx while the dialog is being shown.
• DialogHost was not set
• Only one ContentDialogHost instance is allowed per Window.

AI-assisted analysis of lepoco/wpfui@ffebacd610 (2026-08-13). Data as JSON: /api/errors/1f23fc0e5569436d. Report an issue: GitHub.