PrismLibrary/Prism · error · ArgumentNullException

ArgumentNullException(nameof(navigation))

Error message

ArgumentNullException(nameof(navigation))

What it means

The RequestNavigate extension overload (INavigateAsync, string target, Action<NavigationResult> callback) validates its arguments before parsing the target and delegates to navigation.RequestNavigate. Passing null for the navigation object throws ArgumentNullException(nameof(navigation)).

Solutions

1. Ensure the INavigateAsync instance (typically an IRegion) is non-null before calling — check region resolution succeeded.
2. Guard the source of the region (e.g. regionManager.Regions["X"] existence) before invoking.
3. If region may not exist, use regionManager.RegisterViewWithRegion or check Regions.ContainsRegionWithName first.

Example fix

// before
regionManager.Regions["MainRegion"].RequestNavigate("Home"); // may be null if region missing
// after
if (regionManager.Regions.ContainsRegionWithName("MainRegion"))
    regionManager.Regions["MainRegion"].RequestNavigate("Home");

if (navigation == null)
    throw new InvalidOperationException("Region not available for navigation");

static bool CanNavigate(IRegionManager rm, string regionName) =>
    rm != null && rm.Regions.ContainsRegionWithName(regionName);

try { region.RequestNavigate(target, result => {}); }
catch (ArgumentNullException ex) { logger.LogWarning(ex, "Navigation target not initialized"); }

When it happens

Trigger: Calling RequestNavigate(null, "SomeView", callback) — e.g. the region or INavigateAsync instance was never initialized or a null return from a factory was passed through.

Common situations: Region not yet attached (region lookup returned null and was passed in); calling the extension before region creation; unit tests passing null mocks.

Related errors

• ArgumentNullException(nameof(target))
• ArgumentNullException for 'regionName'
• ArgumentNullException for 'regionTarget'
• ArgumentNullException for 'target'
• ArgumentNullException for 'view'

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/408d82398e33b663. Report an issue: GitHub.

Appendix: source

Thrown at src/Prism.Core/Navigation/Regions/NavigationAsyncExtensions.cs:43

        /// Initiates navigation to the target specified by the <paramref name="target"/>.
        /// </summary>
        /// <param name="navigation">The navigation object.</param>
        /// <param name="target">The navigation target</param>
        public static void RequestNavigate(this INavigateAsync navigation, string target)
        {
            RequestNavigate(navigation, target, nr => { });
        }

        /// <summary>
        /// Initiates navigation to the target specified by the <paramref name="target"/>.
        /// </summary>
        /// <param name="navigation">The navigation object.</param>
        /// <param name="target">The navigation target</param>
        /// <param name="navigationCallback">The callback executed when the navigation request is completed.</param>
        public static void RequestNavigate(this INavigateAsync navigation, string target, Action<NavigationResult> navigationCallback)
        {
            if (navigation == null)
                throw new ArgumentNullException(nameof(navigation));

            if (target == null)
                throw new ArgumentNullException(nameof(target));

            var targetUri = new Uri(target, UriKind.RelativeOrAbsolute);

            navigation.RequestNavigate(targetUri, navigationCallback);
        }

        /// <summary>
        /// Initiates navigation to the target specified by the <see cref="Uri"/>.
        /// </summary>
        /// <param name="navigation">The navigation object.</param>
        /// <param name="target">The navigation target</param>
        public static void RequestNavigate(this INavigateAsync navigation, Uri target)
        {
            if (navigation == null)
                throw new ArgumentNullException(nameof(navigation));

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