unoplatform/uno · error · InvalidOperationException

Failed to load {e.SourcePageType.FullName}: {e.Exception}

Error message

Failed to load {e.SourcePageType.FullName}: {e.Exception}

What it means

Default OnNavigationFailed handler in the Uno 5.3 solution template (uno53net9blank). Identical contract to other Uno templates: the Frame raises NavigationFailed when a page cannot be loaded, and the template wraps the inner exception into an InvalidOperationException that re-throws and terminates the app. It exists to make navigation failures impossible to ignore during dev.

Source

Thrown at src/SolutionTemplate/5.3/uno53net9blank/uno53net9blank/App.xaml.cs:61

            // When the navigation stack isn't restored navigate to the first page,
            // configuring the new page by passing required information as a navigation
            // parameter
            rootFrame.Navigate(typeof(MainPage), args.Arguments);
        }

        MainWindow.SetWindowIcon();
        // Ensure the current window is active
        MainWindow.Activate();
    }

    /// <summary>
    /// Invoked when Navigation to a certain page fails
    /// </summary>
    /// <param name="sender">The Frame which failed navigation</param>
    /// <param name="e">Details about the navigation failure</param>
    void OnNavigationFailed(object sender, NavigationFailedEventArgs e)
    {
        throw new InvalidOperationException($"Failed to load {e.SourcePageType.FullName}: {e.Exception}");
    }

    /// <summary>
    /// Configures global Uno Platform logging
    /// </summary>
    public static void InitializeLogging()
    {
#if DEBUG
        // Logging is disabled by default for release builds, as it incurs a significant
        // initialization cost from Microsoft.Extensions.Logging setup. If startup performance
        // is a concern for your application, keep this disabled. If you're running on the web or
        // desktop targets, you can use URL or command line parameters to enable it.
        //
        // For more performance documentation: https://platform.uno/docs/articles/Uno-UI-Performance.html

        var factory = LoggerFactory.Create(builder =>
        {
#if __WASM__

View on GitHub (pinned to 0418340488)

Solutions

1. Read e.Exception (the inner exception) — it holds the actual failure; the page name in the message is only context.
2. Confirm the page type compiles into the active TFM and that x:Class matches the fully-qualified type name.
3. Run the page constructor under the debugger to catch the first-chance exception before the wrapper re-throws.
4. Swap the throw for diagnostics + e.Handled=true with a fallback page if you need graceful degradation in production.

Example fix

// before
void OnNavigationFailed(object sender, NavigationFailedEventArgs e)
{
    throw new InvalidOperationException($"Failed to load {e.SourcePageType.FullName}: {e.Exception}");
}

// after
void OnNavigationFailed(object sender, NavigationFailedEventArgs e)
{
    _logger.LogError(e.Exception, "Navigation failed for {Page}", e.SourcePageType?.FullName);
    e.Handled = true;
}

static bool CanNavigate(Frame f, Type page) => page != null && f.Content?.GetType() != page;

try { frame.Navigate(pageType); } catch (InvalidOperationException) { log.Error($"Navigation to {pageType} failed"); frame.Navigate(typeof(ErrorPage)); }

When it happens

Trigger: Frame.Navigate to a page whose constructor or XAML initialization throws, or to a type that cannot be activated on the running platform (net9 blank target).

Common situations: Newly added page not wired into the project, x:Class/namespace mismatch, missing dependency injection registration for a page constructor parameter, or a platform guard (#if) excluding the page on the active target.

Related errors

• Failed to load {e.SourcePageType.FullName}: {e.Exception}
• Failed to load {e.SourcePageType.FullName}: {e.Exception}
• Failed to load {e.SourcePageType.FullName}: {e.Exception}
• Failed to load {e.SourcePageType.FullName}: {e.Exception}
• Failed to load {e.SourcePageType.FullName}: {e.Exception}

AI-assisted analysis of unoplatform/uno@0418340488 (2026-08-13). Data as JSON: /api/errors/4b76b085fbc9fca7. Report an issue: GitHub.