dotnet/maui · error · ArgumentNullException

before

Error message

before

What it means

InsertPageBefore(page, before) inserts a page before an existing 'before' page. It immediately calls Platform.GetRenderer(before).ViewController (line 575), so 'before' must be non-null and must already have a renderer; the null guard rejects a null 'before' early.

Source

Thrown at src/Compatibility/Core/src/iOS/Renderers/NavigationRenderer.cs:569

		}

		[PortHandler]
		void UpdateUseLargeTitles()
		{
			if (Forms.IsiOS11OrNewer && NavPage != null)
				NavigationBar.PrefersLargeTitles = NavPage.OnThisPlatform().PrefersLargeTitles();
		}

		[PortHandler]
		void UpdateTranslucent()
		{
			NavigationBar.Translucent = NavPage.OnThisPlatform().IsNavigationBarTranslucent();
		}

		void InsertPageBefore(Page page, Page before)
		{
			if (before == null)
				throw new ArgumentNullException("before");
			if (page == null)
				throw new ArgumentNullException("page");

			var pageContainer = CreateViewControllerForPage(page);
			var target = Platform.GetRenderer(before).ViewController.ParentViewController;
			ViewControllers = ViewControllers.Insert(ViewControllers.IndexOf(target), pageContainer);
		}

		void OnInsertPageBeforeRequested(object sender, NavigationRequestedEventArgs e)
		{
			InsertPageBefore(e.Page, e.BeforePage);
		}

		void OnPopRequested(object sender, NavigationRequestedEventArgs e)
		{
			e.Task = PopViewAsync(e.Page, e.Animated);
		}

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Ensure 'before' is a page currently on the NavigationPage stack and has been pushed/rendered.
2. Use NavigationPage.GetPath / inspect Navigation.NavigationStack to confirm the target page exists.
3. Null-check 'before' before calling InsertPageBefore.

Example fix

// before
Navigation.InsertPageBefore(newPage, maybeNullPage);

// after
if (Navigation.NavigationStack.Contains(maybeNullPage))
    Navigation.InsertPageBefore(newPage, maybeNullPage);

if (before == null) throw new ArgumentNullException(nameof(before));
if (!Navigation.NavigationStack.Contains(before)) return;
Navigation.InsertPageBefore(page, before);

When it happens

Trigger: Calling Navigation.InsertPageBefore(page, null) - e.g. the 'before' page reference was not resolved, or a page lookup returned null because the page is not currently on the stack.

Common situations: Inserting before a page that has been popped/removed; passing the wrong page reference; calling InsertPageBefore before the target page is rendered.

Related errors

• page
• InsertPageBefore is not supported globally on Android, pleas
• InsertPageBefore is not supported globally on iOS, please us
• PopAsync is not supported globally on iOS, please use a Navi
• PopToRootAsync is not supported globally on iOS, please use

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/243b6ae4643d2dd3. Report an issue: GitHub.