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 MyAppXamlTrim solution template (XAML trimming scenario). The Frame raises NavigationFailed when a page cannot be instantiated; the template wraps the inner exception and re-throws as InvalidOperationException, crashing the app. In a trimming-aware app this commonly fires when trimming has removed a page type or its members.

Source

Thrown at src/SolutionTemplate/MyAppXamlTrim/MyAppXamlTrim.Shared/App.xaml.cs:100

				{
					// 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);
				}
				// 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>
		/// Invoked when application execution is being suspended.  Application state is saved
		/// without knowing whether the application will be terminated or resumed with the contents
		/// of memory still intact.
		/// </summary>
		/// <param name="sender">The source of the suspend request.</param>
		/// <param name="e">Details about the suspend request.</param>
		private void OnSuspending(object sender, SuspendingEventArgs e)
		{
			var deferral = e.SuspendingOperation.GetDeferral();
			//TODO: Save application state and stop any background activity
			deferral.Complete();
		}

		/// <summary>
		/// Configures global Uno Platform logging

View on GitHub (pinned to 0418340488)

Solutions

1. Inspect e.Exception for the underlying failure (often TypeLoadException or MissingMethodException under trimming).
2. Add trim/AOT roots for the page and types it references (DynamicDependency attributes, rd.xml, or TrimmingRoots), or mark the page with a dynamic-availability attribute.
3. Verify the page type is still present in the trimmed binary with a linkage check.
4. For production resilience, log + set e.Handled=true and navigate to a fallback page instead of re-throwing.

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 (trim?): {Page}", e.SourcePageType?.FullName);
    e.Handled = true;
}

// trim-specific: ensure the type is present in the trimmed binary
static bool TypePresent(Type t) => t != null && t.GetConstructor(Type.EmptyTypes) != null;

try { frame.Navigate(pageType); } catch (InvalidOperationException ex) { log.Error(ex, $"Nav failed (trim?): {pageType}"); frame.Navigate(typeof(ErrorPage)); }

When it happens

Trigger: Frame.Navigate to a page that was trimmed away, whose constructor/member was trimmed, or that throws during initialization under the trimmed binary.

Common situations: XAML trimming/AOT removed the page type or a referenced type; missing DynamicDependency/DeserializeXaml roots; reflection-based activation failing; constructor throwing because a dependency was trimmed.

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/f8ccad9660ebcb98. Report an issue: GitHub.