PrismLibrary/Prism · error · InvalidOperationException

The Scoped Provider has already been assigned to another…

Error message

The Scoped Provider has already been assigned to another page. Expected: '{page.GetType().FullName}' - Found: '{accessor.Page.GetType().FullName}'.

What it means

Prism's Navigation attached property (Navigation.Scope) validates that an IScopedProvider is bound to exactly one page. OnNavigationScopeChanged resolves IPageAccessor from the scoped provider; if the provider's Page is already set to a different page, it throws InvalidOperationException, because sharing one scoped service provider across pages would leak scoped state.

Solutions

1. Create a new IScopedProvider per page; never reuse one across pages.
2. Only set Navigation.Scope with the provider created for that exact page (e.g. via Prism's navigation pipeline).
3. If re-navigating, clear/rebuild the scope instead of reassigning it.
4. Check for duplicate Scope assignments in XAML and code-behind.

Example fix

// before: reusing parent's scope on child page
childPage.SetValue(Navigation.ScopeProperty, parentScope);
// after: let Prism create the scope per page, or create a fresh one
var childScope = scopeFactory.CreateScopedProvider(childPage);
childPage.SetValue(Navigation.ScopeProperty, childScope);

if (scopedProvider.Resolve<IPageAccessor>() is { } accessor && accessor.Page is not null && accessor.Page != page)
    throw new InvalidOperationException("Scoped provider already bound to a different page");

if (newValue is IScopedProvider sp && sp.Resolve<IPageAccessor>().Page is null) { /* safe to attach */ }

try
{
    Navigation.SetScope(page, scopedProvider);
}
catch (InvalidOperationException ex) when (ex.Message.Contains("Scoped Provider"))
{
    logger.LogError(ex, "Scoped provider reused across pages");
}

When it happens

Trigger: Setting Navigation.ScopeProperty with an IScopedProvider whose IPageAccessor.Page already holds a different page — typically reusing the same scoped provider instance across two pages or assigning the scope property twice with different pages.

Common situations: Manually assigning Navigation.Scope in XAML/code with a provider created for another page; creating one scope in a parent page and attaching it to a pushed child page; navigation page reuse where the provider wasn't reset.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• The page type ' ' is not supported.
• Unable to determine the current page.
• NavigationException.NoPageIsRegistered
• The builder does not implement IRegistryAware
• NavigationException.NoPageIsRegistered

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/517b55f04862440d. Report an issue: GitHub.

Appendix: source

Thrown at src/Maui/Prism.Maui/Navigation/Xaml/Navigation.cs:46

    {
        if (bindable is not Page page || oldValue == newValue)
        {
            return;
        }

        if (oldValue != null && newValue is null && oldValue is IScopedProvider oldProvider)
        {
            oldProvider.Dispose();
            return;
        }

        if (newValue != null && newValue is IScopedProvider scopedProvider)
        {
            var accessor = scopedProvider.Resolve<IPageAccessor>();
            if (accessor.Page is null)
                accessor.Page = page;
            else if (accessor.Page != page)
                throw new InvalidOperationException($"The Scoped Provider has already been assigned to another page. Expected: '{page.GetType().FullName}' - Found: '{accessor.Page.GetType().FullName}'.");

            scopedProvider.IsAttached = true;
        }
    }

    /// <summary>
    /// Provides bindable CanNavigate Bindable Property
    /// </summary>
    public static readonly BindableProperty CanNavigateProperty =
        BindableProperty.CreateAttached("CanNavigate",
            typeof(bool),
            typeof(Navigation),
            true,
            propertyChanged: OnCanNavigatePropertyChanged);

    internal static readonly BindableProperty RaiseCanExecuteChangedInternalProperty =
        BindableProperty.CreateAttached("RaiseCanExecuteChangedInternal",
            typeof(Action),

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