PrismLibrary/Prism · error · KeyNotFoundException

No registration found for the Region View

Error message

No registration found for the Region View '{viewType.FullName}'.

What it means

RegionViewRegistry.RegisterViewWithRegion(Type) resolves a factory that looks up the view type in IRegionNavigationRegistry.Registrations; if no Region-type registration matches the viewType, a KeyNotFoundException with the view's full name is thrown. The view must first be registered (via ViewType.Region registration) before the region registry can create it.

Solutions

Register the view: navigationBuilder.RegisterView<TView>(...) / RegisterForNavigation<TView>() so a Region-type registration exists.
Verify the exact Type passed to RegisterViewWithRegion matches the registered type (same assembly and full name).
Check that the assembly containing the view is scanned/loaded; ensure IRegionNavigationRegistry contains the expected entry.

Example fix

// before
containerRegistry.RegisterViewWithRegion("MainRegion", typeof(UndefinedView)); // never registered
// after
containerRegistry.RegisterForNavigation<MainView>("MainView");
containerRegistry.RegisterViewWithRegion("MainRegion", typeof(MainView));

Defensive patterns

Strategy: try-catch

Validate before calling

var registered = container.Resolve<IRegionNavigationRegistry>()
    .Registrations.Any(x => x.Type == ViewType.Region && x.View == viewType);
if (!registered)
    throw new InvalidOperationException($"{viewType.FullName} is not registered as a region view");

Type guard

bool IsRegisteredRegionView(IRegionNavigationRegistry reg, Type t) =>
    reg.Registrations.Any(x => x.Type == ViewType.Region && x.View == t);

Try / catch

try { registry.RegisterViewWithRegion(regionName, viewType); }
catch (KeyNotFoundException ex) { Console.WriteLine($"Missing registration: {ex.Message}"); }

Prevention

Always call RegisterForNavigation/RegisterView before RegisterViewWithRegion(Type)
Verify the Type matches the registered one after refactors
Confirm view assemblies are included in registration scanning

When it happens

Trigger: Calling containerProvider.Resolve ... or regionViewRegistry.RegisterViewWithRegion(regionName, typeof(SomeView)) when SomeView was never registered in the DI/region registry (missing navigation registration, e.g. never registered via RegisterForNavigation with Region view type).

Common situations: Forgetting a RegisterForNavigation/registration call during App.RegisterTypes or App.CreateWindow; renaming/moving the view class so the stored registration's Type no longer matches; assembly scanning not including the view's assembly.

Understand the failure class

Background: Record Not Found Errors: "not found", RecordNotFound, and "was not found" — what they mean and how to fix them — this error's family across 28 libraries.

Related errors

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/4cb7258ef94b66fa. Report an issue: GitHub.

Appendix: source

Thrown at src/Maui/Prism.Maui/Navigation/Regions/RegionViewRegistry.cs:57

            items.Add(getContentDelegate(container));
        }

        return items;
    }

    /// <summary>
    /// Registers a content type with a region name.
    /// </summary>
    /// <param name="regionName">Region name to which the <paramref name="viewType"/> will be registered.</param>
    /// <param name="viewType">Content type to be registered for the <paramref name="regionName"/>.</param>
    public void RegisterViewWithRegion(string regionName, Type viewType)
    {
        RegisterViewWithRegion(regionName, c =>
        {
            var registry = c.Resolve<IRegionNavigationRegistry>();
            var registration = registry.Registrations.FirstOrDefault(x => x.Type == ViewType.Region && x.View == viewType);
            if (registration is null)
                throw new KeyNotFoundException($"No registration found for the Region View '{viewType.FullName}'.");

            return registry.CreateView(c, registration.Name);
        });
    }

    /// <summary>
    /// Registers a content type with a region name.
    /// </summary>
    /// <param name="regionName">Region name to which the <paramref name="targetName"/> will be registered.</param>
    /// <param name="targetName">Content type to be registered for the <paramref name="regionName"/>.</param>
    public void RegisterViewWithRegion(string regionName, string targetName)
    {
        RegisterViewWithRegion(regionName, c =>
        {
            var registry = c.Resolve<IRegionNavigationRegistry>();
            return registry.CreateView(c, targetName);
        });
    }

View on GitHub (pinned to 358118cd64)