PrismLibrary/Prism · error · ArgumentNullException

regionName

Error message

regionName

What it means

RegionAdapterBase<T>.Initialize assigns region.Name = regionName, throwing ArgumentNullException when the regionName argument is null. Every region adapter funnels through this method, so a null region name during region initialization is rejected here.

Solutions

1. Ensure the RegionManager.RegionName value (or the regionName argument) is a non-null, non-empty string before the view is attached
2. Guard any bound property feeding RegionName with a fallback value in the ViewModel
3. If registering regions programmatically, pass a literal or validated region name to Initialize

Example fix

// before
stackLayout.SetValue(RegionManager.RegionNameProperty, viewModel.RegionName); // null

// after
if (!string.IsNullOrEmpty(viewModel.RegionName))
    stackLayout.SetValue(RegionManager.RegionNameProperty, viewModel.RegionName);

if (string.IsNullOrEmpty(regionName)) throw new ArgumentException("Region name must be non-empty", nameof(regionName));

try { adapter.Initialize(target, regionName); }
catch (ArgumentNullException) { /* log: region name was null; fix the bound RegionName value */ }

When it happens

Trigger: Calling IRegionAdapter.Initialize(regionTarget, null), typically reached when a control's RegionManager.RegionName attached property is set to null (or bound to a null value) and the region registration pipeline calls Initialize with that value.

Common situations: Binding RegionManager.RegionName to a ViewModel property that is null at bind time; programmatically calling region registration helpers without a name; renaming a region and leaving the bound property unset.

Related errors

• regionTarget
• e
• target
• view
• region

AI-assisted analysis of PrismLibrary/Prism@358118cd64 (2026-09-15). Data as JSON: /api/errors/8ad5bb6a3329021b. Report an issue: GitHub.

Appendix: source

Thrown at src/Maui/Prism.Maui/Navigation/Regions/Adapters/RegionAdapterBase.cs:40

    }

    /// <summary>
    /// Gets or sets the factory used to create the region behaviors to attach to the created regions.
    /// </summary>
    protected IRegionBehaviorFactory RegionBehaviorFactory { get; set; }

    /// <summary>
    /// Adapts an object and binds it to a new <see cref="IRegion"/>.
    /// </summary>
    /// <param name="regionTarget">The object to adapt.</param>
    /// <param name="regionName">The name of the region to be created.</param>
    /// <returns>The new instance of <see cref="IRegion"/> that the <paramref name="regionTarget"/> is bound to.</returns>
    public IRegion Initialize(T regionTarget, string regionName)
    {
        var page = regionTarget.GetParentPage();
        var container = regionTarget.GetContainerProvider();
        IRegion region = CreateRegion(container);
        region.Name = regionName ?? throw new ArgumentNullException(nameof(regionName));
        if (region is ITargetAwareRegion taRegion)
            taRegion.TargetElement = regionTarget;

        var children = page.GetChildRegions(true);
        children.Add(region);

        SetObservableRegionOnHostingControl(region, regionTarget);

        Adapt(region, regionTarget);
        AttachBehaviors(region, regionTarget);
        AttachDefaultBehaviors(region, regionTarget);
        return region;
    }

    /// <summary>
    /// Adapts an object and binds it to a new <see cref="IRegion"/>.
    /// </summary>
    /// <param name="regionTarget">The object to adapt.</param>

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