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 5.6 solution template (uno56droidioswasmskia, multi-target Android/iOS/WASM/Skia). Same as other Uno templates: when Frame navigation to SourcePageType fails, the inner exception is wrapped and re-thrown as InvalidOperationException, crashing the process. Fail-fast design for development.

Source

Thrown at src/SolutionTemplate/5.6/uno56droidioswasmskia/uno56droidioswasmskia/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. Inspect e.Exception for the real cause; the message's page name is secondary context.
2. Test navigation on each target individually to find which platform fails (multi-target template).
3. Check the page's #if guards and resource references resolve on every target the project builds.
4. Replace the throw with logging and set e.Handled=true to navigate to an error page instead of crashing.

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, "Nav failed: {Page}", e.SourcePageType?.FullName);
    e.Handled = true;
    (sender as Frame)?.Navigate(typeof(ErrorPage));
}

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

try { frame.Navigate(pageType); } catch (InvalidOperationException) { log.Error($"Nav failed on multi-target: {pageType}"); frame.Navigate(typeof(ErrorPage)); }

When it happens

Trigger: Frame.Navigate to a page that throws during construction/initialization, or a page type not available on one of the four targets (Android/iOS/WASM/Skia).

Common situations: Platform-conditional code path that breaks on one target, missing asset/resource on WASM, page excluded via #if on the active platform, or a constructor dependency not registered in the host.

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/1a755c845be3871a. Report an issue: GitHub.