PrismLibrary/Prism · error · ArgumentNullException

regionTarget

Error message

regionTarget

What it means

LayoutRegionAdapter.Adapt throws ArgumentNullException(nameof(regionTarget)) when the Layout control to be adapted is null. The adapter cannot attach BindableLayout items to a null target, so this is an internal contract violation by the region infrastructure or a custom caller.

Solutions

1. Confirm the XAML element with prism:RegionManager.RegionName actually exists and instantiates on the target platform.
2. Verify the attached control derives from Layout (the adapter's supported target type).
3. Fix custom callers to pass a concrete Layout instance to Adapt.

if (regionTarget is null) return; // ensure the XAML control resolved on this platform

bool TryGetTarget(Layout control, out Layout target)
{
    target = control;
    return target != null;
}

When it happens

Trigger: Adapt called with a null Layout regionTarget - usually from malformed region registration where the control lookup failed (region name attached to a non-existent control) or a custom adapter invocation.

Common situations: XAML region name set on a control that was removed/replaced so the target resolves null; custom code calling the adapter directly; platform-specific layouts that are not real Layout instances.

Related errors

• region
• regionName
• regionTarget
• e
• target

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/5f3d66b27f339d89. Report an issue: GitHub.

Appendix: source

Thrown at src/Maui/Prism.Maui/Navigation/Regions/Adapters/LayoutRegionAdapter.cs:31

    /// </summary>
    /// <param name="regionBehaviorFactory">The factory used to create the region behaviors to attach to the created regions.</param>
    public LayoutRegionAdapter(IRegionBehaviorFactory regionBehaviorFactory)
        : base(regionBehaviorFactory)
    {
    }

    /// <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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