PrismLibrary/Prism · error · ArgumentNullException

navigationCallback

Error message

navigationCallback

What it means

RequestNavigate validates that the completion callback is non-null before starting navigation, because the NavigationResult must be delivered back to the caller. A null callback makes the asynchronous navigation result unobservable, so Prism throws immediately rather than navigating silently.

Solutions

1. Pass a non-null callback, even a no-op: result => { }.
2. In helper wrappers, substitute an empty lambda when the caller supplies none.
3. Guard the callback at the call site before invoking RequestNavigate.

Example fix

// before
navigationService.RequestNavigate(new Uri("DetailsView", UriKind.Relative), null);
// after
navigationService.RequestNavigate(new Uri("DetailsView", UriKind.Relative), result => { });

if (navigationCallback is null)
    navigationCallback = result => { };
navigationService.RequestNavigate(target, navigationCallback, parameters);

bool HasCallback(Action<NavigationResult> cb) => cb is not null;

try
{
    navigationService.RequestNavigate(target, result => OnNavigated(result));
}
catch (ArgumentNullException)
{
    // supply a callback and retry
}

When it happens

Trigger: Calling region.NavigationService.RequestNavigate(uri, null) or forwarding a callback variable that is null (e.g. an unassigned Action<NavigationResult>).

Common situations: Wrapping navigation in helper methods with an optional callback parameter that is passed straight through; refactoring that dropped the callback lambda.

Related errors

• configureSegment
• regionNavigationContentLoader
• source
• uri
• The page type ' ' is not supported.

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/5e6fc6c4167c0f46. Report an issue: GitHub.

Appendix: source

Thrown at src/Maui/Prism.Maui/Navigation/Regions/Navigation/RegionNavigationService.cs:91

    /// Initiates navigation to the specified target.
    /// </summary>
    /// <param name="target">The target.</param>
    /// <param name="navigationCallback">A callback to execute when the navigation request is completed.</param>
    public void RequestNavigate(Uri target, Action<NavigationResult> navigationCallback)
    {
        RequestNavigate(target, navigationCallback, null);
    }

    /// <summary>
    /// Initiates navigation to the specified target.
    /// </summary>
    /// <param name="target">The target.</param>
    /// <param name="navigationCallback">A callback to execute when the navigation request is completed.</param>
    /// <param name="regionParameters">The navigation parameters specific to the navigation request.</param>
    public void RequestNavigate(Uri target, Action<NavigationResult> navigationCallback, INavigationParameters regionParameters)
    {
        if (navigationCallback == null)
            throw new ArgumentNullException(nameof(navigationCallback));

        try
        {
            DoNavigate(target, navigationCallback, regionParameters);
        }
        catch (Exception e)
        {
            NotifyNavigationFailed(new NavigationContext(this, target), navigationCallback, e);
        }
    }

    private void DoNavigate(Uri source, Action<NavigationResult> navigationCallback, INavigationParameters regionParameters)
    {
        if (source == null)
            throw new ArgumentNullException(nameof(source));

        if (Region == null)
            throw new InvalidOperationException(Resources.NavigationServiceHasNoRegion);

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