dotnet/maui · critical · InvalidOperationException

You MUST invoke LoadApplication () before calling base.Finis

Error message

You MUST invoke LoadApplication () before calling base.FinishedLaunching ()

What it means

DidFinishLaunching calls SetMainPage and _application.SendStart(), which require _application to have been set by LoadApplication. If _application is still null when DidFinishLaunching runs, LoadApplication was never called (or was called after base.FinishedLaunching). The host enforces the ordering: LoadApplication first, then the launching callback.

Source

Thrown at src/Compatibility/Core/src/MacOS/FormsApplicationDelegate.cs:48

			Application.SetCurrentApplication(application);
			_application = application;

			if (NSApplication.SharedApplication.MainMenu != null)
				_storyboardMainMenuCount = (int)NSApplication.SharedApplication.MainMenu.Count;

			application.PropertyChanged += ApplicationOnPropertyChanged;
		}

		public override void DidFinishLaunching(Foundation.NSNotification notification)
		{
			if (MainWindow == null)
				throw new InvalidOperationException("Please provide a main window in your app");

			MainWindow.Display();
			MainWindow.MakeKeyAndOrderFront(NSApplication.SharedApplication);
			if (_application == null)
				throw new InvalidOperationException("You MUST invoke LoadApplication () before calling base.FinishedLaunching ()");

			SetMainPage();
			UpdateMainMenu();
			_application.SendStart();
		}

		public override void DidBecomeActive(Foundation.NSNotification notification)
		{
			// applicationDidBecomeActive
			// execute any OpenGL ES drawing calls
			if (_application == null || !_isSuspended)
				return;
			_isSuspended = false;
			_application.SendResume();
		}

		public override void DidResignActive(Foundation.NSNotification notification)
		{

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Call LoadApplication(app) inside DidFinishLaunching before invoking base.DidFinishLaunching(notification).
2. Confirm LoadApplication is present exactly once and not skipped on any startup path.
3. Follow the standard template order: LoadApplication(app); base.DidFinishLaunching(notification);

Example fix

// before
public override void DidFinishLaunching(NSNotification n)
{
    base.DidFinishLaunching(n); // _application null -> throws
    LoadApplication(new App());
}

// after
public override void DidFinishLaunching(NSNotification n)
{
    LoadApplication(new App());
    base.DidFinishLaunching(n);
}

// Order: LoadApplication before base.DidFinishLaunching
public override void DidFinishLaunching(NSNotification n)
{
    LoadApplication(new App());
    base.DidFinishLaunching(n);
}

When it happens

Trigger: Overriding DidFinishLaunching and calling base.DidFinishLaunching before LoadApplication(application). Or not calling LoadApplication at all in the delegate.

Common situations: Custom AppDelegate that reordered startup calls. Template where LoadApplication was accidentally removed or commented out. Calling base.FinishedLaunching() first then LoadApplication().

Related errors

• call Forms.Init() before this
• application
• Please provide a main window in your app
• NavigationPage must have a root Page before being used. Eith
• You MUST invoke LoadApplication () before calling base.Finis

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/75ef8e43be226d25. Report an issue: GitHub.