PrismLibrary/Prism · error · InvalidOperationException

Resources.LayoutViewHasChildrenException

Error message

Resources.LayoutViewHasChildrenException

What it means

LayoutRegionAdapter.Adapt throws when the target Layout already has children or a BindableLayout.ItemsSource set. The adapter drives the layout's children through BindableLayout.ItemsSource = region.Views, which cannot coexist with developer-supplied children or a bound items source.

Solutions

  1. Empty the layout (remove XAML children) and clear BindableLayout.ItemsSource before region registration.
  2. Or remove the region name and manage children normally if region behavior is not required.
  3. Add views through the region (region.Add / RequestNavigate) rather than declaring them inline.

Example fix

<!-- before -->
<StackLayout prism:RegionManager.RegionName="ItemsRegion">
    <Label Text="Static" />
</StackLayout>

<!-- after -->
<StackLayout prism:RegionManager.RegionName="ItemsRegion" />
Defensive patterns

Strategy: validation

Validate before calling

bool regionOk = !(layout.Children?.Any() ?? false) && !layout.IsSet(BindableLayout.ItemsSourceProperty);
if (!regionOk) throw new InvalidOperationException("Clear children/BindableLayout.ItemsSource before using this layout as a region.");

Try / catch

try { regionManager.RegisterRegions(); }
catch (InvalidOperationException ex) when (ex.Message.Contains("children"))
{
    // empty the layout or remove the region name
}

Prevention

When it happens

Trigger: Registering a region name on a StackLayout/Grid/FlexLayout that already declares XAML children (StackLayout with <Label/> etc.) or sets BindableLayout.ItemsSource in XAML/code.

Common situations: Adding prism:RegionManager.RegionName to an existing layout full of static controls; combining a bound layout with region registration while migrating from MVVM lists to Prism regions.

Understand the failure class

Background: Conflicting config options: "cannot be used together" — configuration validation errors across open-source libraries — this error's family across 162 libraries.

Related errors

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/173208fe30f91058. Report an issue: GitHub.

Appendix: source

Thrown at src/Maui/Prism.Maui/Navigation/Regions/Adapters/LayoutRegionAdapter.cs:37

    /// <summary>
    /// Adapts a <see cref="Layout"/> to an <see cref="IRegion"/>.
    /// </summary>
    /// <param name="region">The new region being used.</param>
    /// <param name="regionTarget">The object to adapt.</param>
    protected override void Adapt(IRegion region, Layout regionTarget)
    {
        if (region == null)
            throw new ArgumentNullException(nameof(region));

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

        bool itemsSourceIsSet = regionTarget.Children?.Any() ?? false || regionTarget.IsSet(BindableLayout.ItemsSourceProperty);

        if (itemsSourceIsSet)
        {
            throw new InvalidOperationException(Resources.LayoutViewHasChildrenException);
        }

        BindableLayout.SetItemsSource(regionTarget, region.Views);
        BindableLayout.SetItemTemplate(regionTarget, new RegionItemsSourceTemplate());
    }

    /// <summary>
    /// Creates a new instance of <see cref="IRegion"/>.
    /// </summary>
    /// <returns>A new instance of <see cref="Region"/>.</returns>
    protected override IRegion CreateRegion(IContainerProvider container) =>
        container.Resolve<Region>();
}

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