PrismLibrary/Prism · error · ArgumentNullException

Value cannot be null. (Parameter 'view')

Error message

Value cannot be null. (Parameter 'view')

What it means

The IContainerRegistry.RegisterForNavigation extension throws ArgumentNullException when the view Type is null. As with the IServiceCollection overload, Prism requires a real Page-derived view type to build a ViewRegistration and register it in the container.

Solutions

1. Pass a concrete Page type: containerRegistry.RegisterForNavigation<MainPage, MainPageViewModel>()
2. Guard reflection lookups: if type is null, throw or log before registering
3. Confirm the module/view assembly is referenced and loaded before registration

Example fix

// before
var viewType = Assembly.GetExecutingAssembly().GetType(viewName);
containerRegistry.RegisterForNavigation(viewType, viewModelType);
// after
var viewType = Assembly.GetExecutingAssembly().GetType(viewName) ?? throw new InvalidOperationException($"View '{viewName}' not found");
containerRegistry.RegisterForNavigation(viewType, viewModelType);

var viewType = Type.GetType(viewTypeName);
if (viewType is null)
    throw new InvalidOperationException($"View type '{viewTypeName}' not found — check assembly qualification");
containerRegistry.RegisterForNavigation(viewType, viewModelType);

bool IsResolvablePageType(string name) => Type.GetType(name) is { } t && typeof(Page).IsAssignableFrom(t);

try
{
    containerRegistry.RegisterForNavigation(viewType, viewModelType);
}
catch (ArgumentNullException ex) when (ex.ParamName == "view")
{
    logger.LogError(ex, "Cannot register navigation: view type is null");
}

When it happens

Trigger: Calling containerRegistry.RegisterForNavigation(null, typeof(MyViewModel)) or passing a null result from reflection-based type resolution (e.g. Type.GetType(name) returning null for an unresolvable assembly-qualified name).

Common situations: Custom app builders registering modules by type name from config; module assemblies not loaded so Type.GetType returns null; typos in fully-qualified type names.

Related errors

• Value cannot be null. (Parameter 'view')
• The view type ' ' is not a type of Page.
• configureSegment
• Cannot destroy .
• The page type ' ' is not supported.

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/ce0cffcd174ad13f. Report an issue: GitHub.

Appendix: source

Thrown at src/Maui/Prism.Maui/Ioc/NavigationRegistrationExtensions.cs:19

using System.Diagnostics.CodeAnalysis;
using Prism.Mvvm;

namespace Prism.Ioc;

public static class NavigationRegistrationExtensions
{
    public static IContainerRegistry RegisterForNavigation<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)] TView>(this IContainerRegistry container, string name = null)
        where TView : Page =>
        container.RegisterForNavigation(typeof(TView), null, name);

    public static IContainerRegistry RegisterForNavigation<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)] TView, [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)] TViewModel>(this IContainerRegistry container, string name = null)
        where TView : Page =>
        container.RegisterForNavigation(typeof(TView), typeof(TViewModel), name);

    public static IContainerRegistry RegisterForNavigation(this IContainerRegistry container, Type view, Type viewModel, string name = null)
    {
        if (view is null)
            throw new ArgumentNullException(nameof(view));

        if (string.IsNullOrEmpty(name))
            name = view.Name;

        container.RegisterInstance(new ViewRegistration
            {
                Type = ViewType.Page,
                Name = name,
                View = view,
                ViewModel = viewModel
            })
            .Register(view);

        if (viewModel != null)
            container.Register(viewModel);

        return container;
    }

View on GitHub (pinned to 358118cd64)