PrismLibrary/Prism · error · ArgumentNullException

ArgumentNullException(nameof(navigationContext))

Error message

ArgumentNullException(nameof(navigationContext))

What it means

The RegionNavigationEventArgs constructor requires a NavigationContext and throws ArgumentNullException when null is passed. Every region navigation event argument must carry the context that describes the navigation.

Solutions

1. Only construct the event args with a valid NavigationContext obtained from the navigation service
2. In custom services, guard against null context before raising events
3. In tests, build a NavigationContext via a NavigationJournal/Uri rather than passing null

Example fix

// before
eventArgs = new RegionNavigationEventArgs(null);
// after
var ctx = new NavigationContext(navigationService, new Uri("/View", UriKind.Relative));
eventArgs = new RegionNavigationEventArgs(ctx);

if (navigationContext == null) return; // or throw InvalidOperationException with context

bool IsValid(RegionNavigationEventArgs a) => a?.NavigationContext != null;

try { RaiseNavEvent(new RegionNavigationEventArgs(ctx)); }
catch (ArgumentNullException ex) when (ex.ParamName == "navigationContext") { log.Error("Navigation raised without context"); }

When it happens

Trigger: Constructing RegionNavigationEventArgs directly (e.g. raising the region's NavigationService events manually or in tests) and passing null instead of an active NavigationContext.

Common situations: Custom INavigationService implementations or unit test mocks that raise RegionNavigation events without a context; refactoring where context is only available after an async boundary.

Related errors

• ArgumentNullException(nameof(navigationContext))
• Resources.NavigationModeNotAvailable
• ArgumentNullException("delegate")
• ArgumentNullException for 'regionName'
• ArgumentNullException(nameof(action))

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/b766ac72aaa80070. Report an issue: GitHub.

Appendix: source

Thrown at src/Prism.Core/Navigation/Regions/RegionNavigationEventArgs.cs:16

using System;

namespace Prism.Navigation.Regions
{
    /// <summary>
    /// EventArgs used with the Navigated event.
    /// </summary>
    public class RegionNavigationEventArgs : EventArgs
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="RegionNavigationEventArgs"/> class.
        /// </summary>
        /// <param name="navigationContext">The navigation context.</param>
        public RegionNavigationEventArgs(NavigationContext navigationContext)
        {
            NavigationContext = navigationContext ?? throw new ArgumentNullException(nameof(navigationContext));
        }

        /// <summary>
        /// Gets the navigation context.
        /// </summary>
        /// <value>The navigation context.</value>
        public NavigationContext NavigationContext { get; }

        /// <summary>
        /// Gets the navigation URI
        /// </summary>
        /// <value>The URI.</value>
        /// <remarks>
        /// This is a convenience accessor around NavigationContext.Uri.
        /// </remarks>
        public Uri Uri => NavigationContext.Uri;
    }
}

View on GitHub (pinned to 358118cd64)